REPORTS ON THE TOTAL SOLAR KOLIPSE F AUGUST 1, 1869. S; NAVAL OBSEBVATORY G01MODOREB.F. SANDS U.S;N. SBPERIHTENDBINT. rmitg of No. Division . Range Shelf. Received 7?M4^?ff... . 1 87; REPORTS ON OBSERVATIONS OF THE TOTAL ECLIPSE OF THE SUN, U GUST 7, 1869 CONDUCTED UNDER THE DIRECTION OF COMMODORE B. F. SANDS, U. S. N SUPERINTENDENT OF THE U. S. NAVAL OBSERVATORY, WASHINGTON, 1). C. WASHINGTON. GOVERNMENT FEINTING OFFICE. 1870. IN THE SENATE OP THE UNITED STATES, February 8, 187U. Kesolceil, (the Souse concurring therein,) That there be printed one thousand extra copies of the report made by the officers of the United States Naval Observatory of the total eclipse of the sun of August seven, eighteen hundred and sixty-nine, for the use of the Senate, two thousand extra copies for the use of the House of Representatives, and five hundred copies for distribution among scientific bodies and individuals by the Superintendent of the United States Naval Observatory. Attest: GEO. C. GORHAM. Secretary. Ix THE HOUSE OF REPRESENTATIVES OF THE UNITED STATES. J/uj/ 12, 1870. Retained, That the House concur in the foregoing resolution of the Senate to print one thousand extra copies of tin; report of the officers of the United States Naval Observatory upon the total eclipse of the sun on the seventh of August, eighteen hundred and sixty-nine, for the use of the Senate, two thousand copies for the use of the House of Representa- tives, and five hundred copies for distribution by the United States Naval Observatory. Attest: I-;\VD. McPHEHSON, Clerk. TABLE OF CONTENTS. Page. Report of Commodore B. F. SANDS, U. S. N 3 Report of Professor SIMON NEWCOMB, U. S. N., on observations of the eclipse, &c., made at Des Moiiies, Iowa, and other places : General report , 6 Description of instruments 7 Phenomena at first contact 8 Plan of search for intra-mcrciirial planets 8 Phenomena of totality 9 APPENDIX A. Comparisons of chronometers 11 B. C. Telegraphic comparison of chronometer with Kessels clock beats 11 1). Observations for local time, 12 K. Times of phases, deduced from the observations, and compared with the tabular times 13 F. Observations of the duration of totality and of other phenomena, by amateur observers 15 I. Near the northern limit 16 II. Near the southern limit 20 III. At points too far within the shadow to be used in fixing its limits 22 Report of Professor AVu.i.iAM HAKKNESS, U. S N., on observations of the eclipse, &c., made at Des Moines, Iowa: Introductory 25 Site of temporary observatory 25 Description of temporary observatory 25 Description of instruments : Photographic telescope 26 Forty-three-inch telescope 26 Spectroscope 27 Polariscopes 30 Six-inch sextant 30 Mercurial artificial horizon 31 Other instruments and apparatus 32 General remarks on observations for time and latitude 32 Observations for time 33 Observations for latitude 37 Telegraphic determination of longitude ; 40 Triangnlatioii connecting the various temporary observatories 49 Geographical position of the Court-house Dome 58 Height of the different stations above the sea 58 Miscellaneous work during the eclipse : 59 Spectroscope observations 60 Identification of bright lines 03 Physical constitution of the corona 04 Physical constitution of red prominences 66 Kesults of spectroscope observations 66 Scale of tints 67 Conclusion 1 67 SCHEDULE A. Record of observat ions for time at Des Moines 68 B. Record of observations for latitude at Des Moines 84 C. Record of observations for time at Washington 96 IV TABLE OF CONTENTS. Page. Report of Professor J. R. EASTMAN, U. 8. N., ou observations of the eclipse, &r., made at Des Moiiies, Iowa : List of instruments 99 Description of instrument!) : Telescope 99 Actinometer 99 Photometer 100 Barometer and thermometers r 101 Chronometers 101 Position of instruments 101 Meteorological observations before and after August 7 , , . 102 Observations on the 7th : State of the weather , '. 103 Phenomena before totality 104 Phenomena during totality : Corona 104 Protuberances 105 Amount of light 106 Observations with the actinoineter, photometer, and solar thermometer 107 Phenomena after totality 107 Performance of actiuometer and photometer 108 Performauce of chronometers 108 Time , 109 TABLE I. Barometer before aud after August 7 110 II. Dry thermometer before and after August 7 110 III. Wet thermometer before and after August 7 Ill IV. Solar thermometer before and after August 7 Ill V. Weather before and after August 7 112 VI. Extreme temperature and rain before and after August 7 114 VII. Mean results from tables I to IV, inclusive 114 VIII. Results from observations with tlie actinometer July 29 aud August 4 . . 115 IX. Results from observations with the photometer July 29 115 X. Actinometer observations August 7 116 XI. Photometer observations August 7 118 XII. Results from photometer observations August 7 119 XIII. Meteorological observations August 7 120 Report of Brevet Major EDWARD CUBTIS, Assistant Surgeon U. 8. A., ou photographic observations of the eclipse made at Dos Moines, Iowa. (Communicated by the Surgeon General U. S. A.) I. Synopsis of operations 123 II. The telescope 124 III. The observatory 127 IV. Preliminary experiments : 1. Determination of the chemical focus 127 2. Selection of photographic formulse 128 3. Estimation of length of exposures 129 4. Plan of operations for the eclipse 131 V. The eclipse -132 VI. The photographs and their teachings : 1. Photographs of the partial phases 135 2. Photographs of the totality 142 VII. Concluding suggestions '. 151 SCHEDULE A. Record of negatives 157 B. Table showing the relative actinic force of the sun at different altitudes 160 C. List of articles forming the equipment of the photographic expedition 162 TABLE OF CONTENTS. -v Page. Report of Mr. J. HOMKU LANK on observations of the eclipse made at Des Moiues, Iowa 165 Report of Mr. W. 8. GII.MAX. Jr., on observations of the eclipse made at St. Paul Junction, Plymouth County, Iowa : Description of station : Description of instruments 173 Weather during the eclipse 174 The eclipse first contact 174 Spots on the sun 175 Appearance of the solar surface 175 Approach of the total phase 175 Minute crescent near the sun 176 Totality 176 The corona - 180 Minute object seen near the sun 180 Planets and stars visible 181 The third contact 181 The last contact 181 SCHEDULE A- Meteorological record 183 B. Comparisons of chronometer for time 183 Times of contact, and of disappearance and reappearance of solar spots 185 Report of Mr. F. W. BAHDWKLL, Aid United States Naval Observatory, on observations of the eclipse made at Bristol, Tennessee 189 Report of Brevet Brigadier General AI.HKKT J. MYER, Chief Signal officer U. S. A., on observations of the eclipse made on White Top Mountain, near Abingdon, Virginia 193 Report of Professor ASAPII HALL, U. S. N., on observations of the eclipse made near Plover Bay, Siberia: Introduction 199 Account of the eclipse y 200 Description of the eclipse by Mr. Rogers 201 Mr. Very's letter 202 Commander Franklin's letter 202 Results of the observations of the eclipse 203 Determination of time, latitude, and longitude 203 Latitude of Illionliouk 211 Latitude of Duutze Head 211 Longitude of Dnntze Head 212 Errors of sextant 212 Magnetic observations 213 Values of magnetic force 216 Observations of the barometer and thermometer , 217 LIST OF PLATES. PLATE I. View of the temporary observatory at Des Moiues, occupied by Professors Harknesg and Eastmau, and Dr. Curtis. II. Ground plan of the above. AA. Observing rooiu. a. Door. 666. Shelves. c. Table. i?. Professor Eastuiau's telescope. f. Professor Harkness's telescope. /. The equatorial for photography. ;/. Tripod stand for chronometer. B. Photographic dark-room. hh. Doors. ii. Dumb-waiters for passing plate-holders in and out of dark-room. kli. Windows, closed by shutters. III. Shelves. i. Trough of water, holding the baths for negatives. . Trough with grooved sides for fixing-bath. o. Sink, composed of a wash-tub with India rubber waste-pipe. p. Barrel of water, with pipe and stop-cock projecting through wall of dark-room. III. Triangulatiou connecting tlie various temporary observatories at Des Moines in August, 1869. IV. Spectroscope used by Professor Harkness. V. Spectra of the corona and red prominences, observed by Professor Harkness. VI. Curves showing the readings of the barometer and thermometer, by Professor Eastmau. VII. Curves shoiying the readings of the wet bulb and sun thermometers, by Professor Eastmau. VIII. Curves showing the readings of the actinoineter and photometer, by Professor Eastmau. IX. Colored drawings of the totally eclipsed sun as seem at Des iloines, by Professor Eastman. X. Fac-simile of Dr. Curtis's first photograph of the totally eclipsed sun at Des Moines. XI. Fac-simile of Dr. Curtis's second photograph of the totally eclipsed sun at Des Moiues. XII. Colored drawing of the totally eclipsed sun as seen at St. Paul Junction, Plymouth County, Iowa, by Mr. Oilman. REPORT COMMODORE B. F. SANDS, U. S. N. REPORT OF COMMODORE B. l\ SANDS, U. S. UNITED STATES NAVAL OBSERVATORY, Washington, October L'U, 1809. SlE: In order that the Naval Observatory should perform ils part in the observations of the eclipse of the 7th of August, of this year, and take its proper share of duty on this interesting- occa- sion, which has engaged the attention of all astronomers, 1 early took measures towards organizing parties of officers from this observatory, to be stationed for that purpose at suitable localities upon the path of totality. It was desirable to have a party as far to the northward and westward as possible, but the uncertainty of the weather in those northern regions of our own possessions caused me to hesitate about detailing one of our own officers for so long a journey, with doubts of success and consequent loss of his services here; but at the suggestion of Professor Cottin, in charge of the United States Nautical Almanac, that Plover Hay, on the western side of P>ehring Strait, would possibly give a better chance for good observations, and Professor Asaph Hall, United States Navy, of this observa- tory, volunteering for the duty, he was, at my request, ordered by the department to proceed to San Francisco, whence one of onr naval vessels would take his party to such station at Bchring Strait as he might select . Mr. Joseph A. liogers, of the Ilydrographic OtUce, was detailed to accompany him. They sailed from New York on the 21st of May, and arrived at the station selected in ample time; were fully prepared, and with every encouragement for most interesting results, when, unfortunately for entire success, the contingency occurred which 1 so much feared, and the observation of the eclipse was not so perfect as we desired, on account of partial obscuration, at intervals, by clouds, from just before the ingress till after the egress. The very interesting report of Professor Hall will tell its own tale. Valuable results were obtained, so that the expedition was not altogether futile. Professors Simon Newcomb, William Hark ness, and J. K. Eastman, United States Navy, were ordered by the department, at my request, to proceed to DCS Moines, Iowa, and select such stations within one hundred miles of that locality as should be most suitable for their separate duties. Pro- fessor Newcomb to observe the corona and search for intra -mercurial planetoids, according to his suggestion in a paper in Silliman's Journal for May last ; Professor llarkness with his spectroscope for spectra] analysis, and Professor Eastman for meteorological observations. Surgeon General J. K. Barnes, United States Army, entered with great interest into onr plans, and kindly detailed Assistant Surgeon Brevet Major Edward ( 'nrtis, United States Army, an officer skilled in photography, and assistants, to accompany the observatory party. for the purpose of pho- tographing the totality and various phases of the eclipse. Vice- Admiral Porter kindly loaned the large equatorial telescope of the Naval Academy for the purpose, and a small temporary observatory was erected in our grounds here, where Dr. Curtis passed several weeks in practice and preparation for his interesting work, and he has been rewarded for his labor by photographs which can scarcely be excelled. The observatory not having an instru- ment ready for reading off the photographs obtained, that work wilJ be put in hand at once as soon as the instrument is made, and the results will be published immediately. Upon their arrival at DCS Moines all these ollicers selected that locality as the best for their several observations; Professors llarkness and Eastman, and Dr. Curtis, uniting and erecting one observatory, and Professor Newcomb occupy ing another in a different part of the city for his observa- tions. Mr. V. W. Bawlwell, "Aid," was sent to Bristol, Tennessee, for additional observations upon the corona, leaving on duty at the observatory only Prqiessor Yarnall and Aids Doolittle and Frisby. 4 REPORT OF COMMODORE SANDS. I addressed circular letters to the postmasters on tbe path of totality to interest intelligent observers and forward their results to this observatory, and the newspapers generally published our instructions to observers. From these reports \ve reap a good harvest of information, which, although not purely scientific, has been discussed at the observatory and embodied in the report of Professor Newcomb. To do full justice to these officers (army and navy) of the observatory parties engaged in these observations, and the object for which they were undertaken, I cannot do better than submit their able reports in full, with accompanying plates and illustrations. I have been favored with most intelligent and interesting reports from private scieniilic parties, which I append to this communication. One of them is from Mr. W. S. Oilman, jr., of New York, who has a small observatory at the Palisades, and lias passed his leisure hours in the study of astronomy, making a specialty of solar physics, and who, at his own expense, witli several assistants, went to Iowa to observe the eclipse. It is to be regretted that he could not himself, consistently with his plan of operations, have observed with his large-power telescope the " star" and "crescent" reported by his assistants, who were not experts as he was. The others are from .Mr. J. Homer Lane, of this city, a gentleman who accompanied the Coast Survey party of Professor Hilgard to Des Moines, and from Brevet Brigadier Oeueral A. J. Myer, chief signal officer United States Army, accompanied by Colonel W. Wiuthrop, United States Army, who had a fine position on the summit of White Top Mountain, near Abingdon, Virginia. We are greatly indebted to Mr. William Orton, president of the Western Union Telegraph ( '0111- pany, and Mr. Charles A. Tinker, general manager of the same company, for the free use of their telegraph wires on the evening of the eclipse, and certain hours for several days previously, for the exchange of time-signals bet ween the stations and our observatory here ; and also to .Mr. M. Marean, telegraph operator of the same company, who attended night and day at the observatory to receive and send communications. Our acknowledgments are also due to the many amateur observers on the line of totality who took the trouble to send us their observations, from which we have gleaned much information that is serviceable in our reports. I have the honor to be, very respectfully, your obedient servant, B. F. SANDS, Commodore, Superintendent. Hon. GEO. M. KOBESON, Secretary of the Navy, Washington REP OIR T PROFESSOR SIMON NEWCOMB, U. S. N REPORT OF PROFESSOR NEWCOMB, U. S. N. UNITED STATES NAVAL OBSERVATORY, Washington, September 20, 1809. SIR : I liave the honor to present the following report of my observations on the total eclipse of August 7th last. In obedience to the orders of the department and of yourself, I left Washington on July 28th, and arrived in Des Moines on the 31st. I took with me the following instruments : The observatory comet-seeker, of four inches aperture, equatorially mounted. The object-glass of the transit circle, aperture eight and one-half inches, focal length twelve feet one inch. The object-glass of the refraction circle, aperture six inches, focal length about nine feet. A Gambey sextant from the Hydrographic Office, reading to ten seconds of arc, with artificial horizon. Mean-time chronometer, Negus No. 12S 1 . On my arrival I found the temporary wooden mounting for the extra object-glasses, which you had directed Professor Harkness to have made, quite ready for me. They were of the following construction : Two pieces of 8" by 8" timber were firmly set in the ground to the depth of three feet, the distance between them being twenty-seven inches. A strong frame, of two-inch stuff, twenty- seven inches long, passed between them, turning on a horizontal axis. Through the center of this frame passed the substitute for the telescope tube, consisting of a box twelve inches square and twelve feet long, blackened on the inside and open at both ends. The object-glass was fastened into one end, the eye-piece into the other. It turned in the frame on an axis at right angles to the other axis, but admitting of a motion of only about twenty-five degrees on each side. Connecting rods pass from near the bottom of each post to near the eye-end of the telescope, where they could be clamped with a button, and the telescope thus be fixed in any required position. If 1 had the eclipse to observe over again I should try to make the mounting an equatorial one, by pointing the axis of the frame towards the pole. After an examination of different localities I selected as my observing station a point in the yard of the county court-house, near the Coast Survey longitude station. It is nearly a mile south, and nearly 1 s west of Professor Harkness's observatory. From data obtained privately from other parties, I concluded that the position of my station was very nearly as follows : Latitude 41 35' 4" West longitude from Washington I 1 ' G m 17 8 .0; a result which I do not think can be in error by as much as 2" in latitude, or 1 s in longitude. The occupation of a station near my lodgings and near workshops, stores, &c., saved much trouble and expense. It is just to state that it was only through official courtesies rendered by the following gentlemen that 1 was enabled successfully to occupy a station so convenient, namely, his honor J. II. Hatch, mayor of Des Moines, his honor J. li. Miller, judge of the county court, and Hoyt Sherman, esq. A position was chosen, such that the gable end of the court-house could be used in mounting the screens. A horizontal arm was made to project several feet to the north of the roof. On this arm were mounted three circular screens of 15, 18, and 21 inches diameter, in such a position that they would just hide the sun from points near the south end of my observatory during the total eclipse. Their diameters as measured with a sextant from the observatory were respectively 33', 8 REPORT OF PROFESSOR NEWCOMB. 39', and 46', the largest one being farthest out. The comet-seeker was mounted near the south end of the observatory, so that the outer screen could be made to hide the corona by sliding it out. Xext to the north was the transit-circle glass, and then the inch glass. The observatory consisted only of four walls of rough boards to protect the observers against intrusion and the instruments from the wind. In mounting the instruments I was altogether without assistance except that of the carpenter and of occasional volunteers, curious to see the inside of our walls. On Thursday, however, I pro- cured through Professor Safford the assistance of Mr. Armstrong, a student in the University of Chicago, whose zeal and alacrity rendered his services very valuable. I also, as authorized by you. tendered the use of my wooden telescopes to Professor John Fraser, president of the University of Kansas, and Mr. J. II. Lane, of Washington, the former taking the transit glass, the latter that of the refraction circle. I requested them to make their reports directly to yon. Mr. Armstrong beat the seconds at the chronometer, counting every tenth one aloud. During the two days preceding the eclipse the heavens were covered with clouds, brought on by an east wind, and on Friday there was inist enough to make the ground in our iuclosure too muddy for convenience. On Saturday morning the clouds cleared away, leaving a dense haze. This haze grew thinner in the course of the day, but did not entirely vanish. In observing the contacts 1 used the comet-seeker with an aperture reduced to one inch, a power of 40, and a yellow shade. As thus seen, the definition of the limb was very fine. The eye-piece was furnished with four coarse black bands, arranged as in the margin, with a pair of fine spider lines between them. Turning the ocular twenty degrees from the position in which the sun traveled along the wire, the point of the liinb where the first contact was to take place was parallel to one set of wires, and I thus knew exactly where to look. At chronometer time I saw the minutest visible notch exactly at the expected point of contact. For two or three seconds I was in some doubt whether it was really the moon's limb ; but in three seconds more the limb first above and then below the notch began to assume the sharp, rough character peculiar to the moon's limb, and left no doubt on the subject. As the first part of the moon which impinged on the sun was a quite prominent mountain, I think the time 9 h 5G"' 3 8 .5 may be taken as the time at first contact of the general contour of the moon with that of the sun, as it resulted from my observation. But the observation at 2 s .O was very precise and satisfactory. In about five minutes from the commencement I placed one set of wires parallel to the line of cusps, and noted the moment at which the line of cusps extended between the internal edges of the other thick wires. This took place at chronometer time 10 h I- 1 31 s an observation of which I felt sure within a second. The space thus measured by the cusps was soon afterward determined by transits of the sun's limb over it. Coming now to the preparations for total phase, I remark that the main object I kept in view was to determine whether there was anything at all visible outside the usually assigned limits of the corona, and yet so near the sun as to be invisible at other times. More especially was it determ- ined to search in the neighborhood of the sun for an immense group of very minute intra-inercurial planets, the existence of which had been rendered so probable by the researches of Le Verrier on the motion of Mercury. In making this search my plan was to set two of the telescopes the 8" and 4" in known directions, by pointing each of them on the sun at some definite moment, ten or fifteen minutes before the commencement of totality, and immediately after the latter phase to make a map of any objects that might be seen in either field of view ; then to move the telescope into dif- ferent positions and count the objects in each field of view. OBSERVATIONS OF THE ECLIPSE OP AUGUST 7, J869. 9 After thus sotting- the telescopes, and removing the caps and colored glasses, I got into a nearly dark box, requesting President Fraser to call when he saw the sunlight was just about to disappear. A minute or two before the advent of darkness a crowd of people who had taken their position on the roof of the court-house greeted the progress of the phenomenon with loud and prolonged cheering, rendering me quite uneasy for our time observations. But I think they grew quite silent before the sun had entirely disappeared, and did not renew their cheers on its reappearance. I emerged from the box a few seconds before total darkness, but did not look up until Professor Fraser had given me the word. I then took a single glance at the corona through two thicknesses of green glass. I then attempted to hide the corona behind the outer and the larger of the screens, and thought I had done so, but after the total phase had passed I was convinced that I had mis- taken the moon itself for the screen. Though I knew theoretically that the sky in the direction of the moon ought to seem darker than that outside of the corona, I was wholly unprepared for so strong an illusion of a black globe hanging in mid-air. The corona itself was far less bright than I had anticipated. I then looked most carefully along the direction of the ecliptic to ascertain whether then; was ;in,v appearance of a blush of light extending out in that direction, but I could not perceive the faintest trace of any. I next went in succession to the two telescopes, but not an object was visible in either. I then swept somewhat at random, but near the ecliptic with the comet-seeker, without finding anything. As any isolated object I might find would not only be incapable of certain identification, bat would fail to fulfill the condition of accounting tor the motion of the perihelion of Mercury, I could only regard further search as useless, and therefore proceeded to the study of the corona. But 1 first took a general view of the phenomenon through the comet-seeker, with the full aperture and no screen. Nearly or quite the entire corona was then visible at a single view. As thus seen, I regret that I can describe it with no more accuracy than as an effulgence which, while not at all dazzling to the eye, was yet glorious beyond description. An immense protuberance on the upper side of the inverted corona attracted my attention. During the hurried inspection 1 made of it, the follow- ing points were noticed : 1. It did not seem materially brighter than the corona; it could be viewed directly without the eye being at all dazzled. 2. The large predominance of red in its color was so evident and so strongly marked that I could not entertain a doubt of its reality. The tint was a most beautiful pink. .'5. Its structure was not uniform, nor did the protuberance bear the slightest resemblance to a name. It looked like an immense pile of cumulus clouds, illuminated by a white and red sun, and thus exhibiting different shades of color as the light from the one sun or the other chanced to pre- dominate at different points. Leaving the telescope, I returned to naked-eye observations. Looking directly at the corona, there was no actual appearance of striation, but it seemed to be of a jagged outline, extending out into four sharp points, nearly in the horizontal and vertical direction, while midway between these points the serrated edge hardly seemed to extend beyond the body of the moon. The greatest dis- tance to which the extreme points seemed to extend did not exceed a semi-diameter of the moon, and there was nothing like long rays of light extending out in any direction whatever. When I turned my head, the points did not seem to turn with it. Still, I experienced a singular difficulty iu judging accurately either of the number or direction of the jagged points, or of the extent to which they might be optical illusions, produced by the differences in the height and brilliancy of different parts of the corona. The green glass, however, settled the latter question. Seen through this medium the corona consisted simply of four or five prominences, extending around the moon, smooth in their outline, shading off by imperceptible gradations and rising to different heights, the greatest height not exceeding four or five minutes. The accom- panying sketch gives a general idea of the impression produced by the view through the colored glass, but must not be taken as a drawing of the actual phe- nomenon. I have no doubt that the serrated appearance of the corona and the pointed rays, were purely optical results of the irregular heights of the prominences. A fish-tail 2* 10 REPORT OF PROFESSOR NEWCOMB. gas-light, seen against a dark ground at a distance of fifty yards or more, presents to my eye a simi- lar appearance. I observed the end of totality with the naked eye at 11" 1"' 2G* chronometer time. Mr. Armstrong had continued the counting and beating of the chronometer seconds through the entire period of totality, without once raising his eyes from the chronometer. The reappearance of sunlight was preceded by a general illumination of the atmosphere, commenc- ing three or four seconds before the actual blazing forth of the sun. Two or three minutes before the end of the eclipse, at [ll h 57'"] -.'! s chronometer time,* the chord of cusps measured a space between one fine middle wire, and an edge of one parallel coarse wire which had been found to be passed over by the sun in 27 S .1.5, a mean of four observations. The last contact I observed at 1 1 1 ' .~>S'" i>4 s .5. The outline of the moon was quite smooth and regular near the point of last contact. Accompanying this report are the following papers, which I respectfully request may be con- sidered as forming part of it : A. Comparisons of my chronometer witli those of other parties engaged in observations of precision. The comparisons were made in order to have as many connections as possible with the work of other independent observers. B. Comparisons of chronometer with the (vessels clock at Washington on the evening (if the eclipse. the clock sending its beats by telegraph. C. A similar comparison made by sending signals to Washington contemporaneously with certain beats of the chronometer. The signals are fouud on the chronograph sheet of August 7. D. Observations with a (lambey sextant to obtain the error of the chronometer on local time. E. Times of the phases concluded from my observations, anil compared with those computed from the tables. F. Summary of observations for the duration of totality at various points near the limits of the shadow, made in pursuance of the circular of instructions sent out by you, and collected from the reports placed in my hands. On these observations I beg leave, to remark that both their number and apparent precision exceed what we had reason to expect. One of my fears in proposing the plan was that we should have manufactured observations sent us, but there are none that I can detect as such. The dis- cordance between the number made near the northern and southern limits is much to be regretted. Those made will, however, I conceive, suffice to fix an apparent relative co-ordinate of the sun and moon within a small fraction of a second of arc. This report having been long delayed by illness, it may not be improper to state that I have in the mean time carefully avoided acquiring any knowledge of the descriptions of other witnesses of the eclipse which could affect my impressions of the optical portion of the phenomena. Very respectfully, your obedient servant, SIMON NEWCOMB, Professor Mathematics, U. 8. N. Commodore B. F. SANDS, U. S. N., Superintendent of U. 8. Naval Observatory. "The hours and minutes are assumed, not having been observed. OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 11 A. Comparisons of cltninoim -ti-r \i'i/nn li'Sl iritli other chronometers at Des Moines. Date. Face of Ne- gns 12*1. Face of chro- nometer. Chronometer. Possessor of chro- nometer. 1869. July 31.2 9 7 59. 3 9 11 Negus 1300 . Professor Harkuess. 9 9 50. 4 9 15 Negus 1319 . Professor llarkuess. Aug. 0.9 4 32 40.0 4 37 50 Negus 1319 ' . Professor llarkuess. 1.9 4 44 49.11 4 50 Negus 1319 . Professor llarkness. 4.0 9 22 40 9 27 52. 4 Negus 1319 . Professor llarkuess. {2 2 50 7 50 54.8"| Karr, in. t., ^ Mr. E. Qoodfeliow, 6.8 2 3 5 7 51 10. 5 I 2 3 16 7 21. 2 j (pocket.) ) 1'. S. Coast Survey. 7.0 ( 7 34 30 t 7 35 5 2 37 59.0^ 2 38 34. 5 > Chronometer } watch. ) Mr. White. 7.2 t 16 20 7 20 7.2) Chronometer f Mr. White. < 17 7 20 47. $ watch. ii 7.2 11 51 30.5 4 50. Fletcher 1?0r Mr. J. E. Hilgarcl. 7.4 3 28 49. 5 6 22 40 Kessels 12*7 Mr. J. E. Hilganl. 7. 1 4 10 2.5 740 Kessels 12*7 Mr. J. E. Ililganl. B. CoiHiHirixoHx ofXcyux 1 -> s l iritli A'c.v.s-r/.v <-lo<-k hciilx, tin xcntfroiu Waxhi at/ton Inj teleffraph^on Aug. 7.3. Double beats, marking beginnings of minute, were received at /I. HI. S, "2 L'4 43.9 11 25 43.7 12 L>f> 43.5 2 27 43.4 2 31 42.7 It. Coincidences of beats at m. 2 2G 30 50: 0. C. Times of reception of 5 -second signals at Washington, sent from De,t Moines in coincidence irith certain beats of chronometer Negus 1281. . Mean Correction of clock Chronometer. ft. m. 8. 3 7 50 55 8 50 55 9 5 15 20 25 30 55 10 3 9 0.0 Time by Kessels clock. ft. i. a. 19 8 13.7 18.7 23.fi 9 13.8 18.8 23.8 28.8 38.9 43.9 48.8 53.9 10 19.1, 24.0 19 9 23.83 27.17 12 REPORT OF PROFESSOR NEWCOMB, D. Double altitudes of the sun's limb, observed tcith Gambey se.rtant by reflection from mercury, at the Court-house, Den Moines, tcith readings of sextant for tangency of limbs of sun, to give inilc.r error, and the concluded results of the observations. READINUS lot! INDEX KliROIi. Date. Off limb. On limb. Remarks. O ' " c / // Aug. 2. 359 27 50 32 359 28 15 31 30 Before observing altitude*. 4.2 359 28 10 31 10 After observing altitudes. 6.9 359 27 50 359 27 30 31 5 ) o 30 r,o } After observing altitudes, 7.9 359 28 10 359 28 10 31 25 I 31 5 J After observing altitudes. 8.2 359 27 30 359 27 30 30 40 ? 30 45 $ After observing altitudes. Date. Time by chronometer. Reading of sextant for double alt. Sun's limb. Chronometer fast of appa- rent time. Remarks. 1869. /I. m. . o / // It. III. 8. Aug. 3. 8 1 29 42.0 49 24 35 U. 6 18 52.5 Adopted index cor. -f 10". 31 27.0 50 3 30 U. 53.0 It. HI. X. 33 20. 5 50 45 55 U. 52.9 Mean 6 18 52. 4 34 56! 5 51 21 45 U. 52.9 Eq. of time .... 5 47. 5 36 14.5 50 48 5 L. 52. 1 Mean time error ... 6 13 4. 9 37 17.0 51 11 25 L. 51.7 38 30.5 51 38 40 L. 52.7 39 21. 51 57 55 L. 51.5 Aug. 4. 2 10 38 41.7 59 9 20 L. 6 18 47.7 Adopted index cor. -)- 14". 40 35.5 58 27 5 L. 48.1 It. in. 8. 42 10. 5 58 54 15 \\ 46. 5 Mean 6 18 47.8 43 19. 5 58 29 u! 48. 1 KII time - 5 45.5 44 39! 5 57 59 10 u. 48! 3 Mian time error ... 6 13 2.3 46 15.0 56 23 30 L. (56. 5) Probably T. limb, with a mistake of 1 47 43.0 56 50 50 U. 48.8 iu the record. The corrected error is 49 33.5 56 9 20 U. 47.9 then 6 h 18 m 47". 9. 50 54. 5 55 38 45 U. 46.9 Aug. 6. 9 3 42 48. 95 48 L. 6 18 29. 6 Adopted index cor. -|- 42". 44 47.2 96 28 5 L. 30.0 h. m. . 45 46. 5 96 48 L. 30. 1 Mean ... 6 18 29. 9 46 58. 97 12 30 L. 28 Eq time - - . 5 27. 9 48 35! 97 44 40 L. 29! Mean time error ... 6 13 2. 50 40. 99 28 50 U. 30.8 51 35.5 99 47 35 U. 29.9 52 37. 100 7 45 U. 30.6 53 31.2 100 25 30 U. 31.2 54 43.0 100 49 30 U. 29.7 Aug. 7. 9 2 59 4. 5 80 9 35 L. 6 18 22. 5 Adopted index cor. + 18". 3 53. 7 80 49 L. 21.5 A. H. S. 2 Tfi 1 81 26 2 L. 21.2 Mean 6 18 22. 2 - " '. O 4. 5.5 81 57 35 L! 22 6 Eq. time 5 20. 7 5 49! 7 82 34 50 L. 22.2 Mean time error ... 6131.5 7 56.7 84 23 15 u. 23.2 9 11.6 84 49 55 U. 22.8 12 21.5 85 57 30 U. 22.7 13 31.5 86 22 41 U. 21.5 14 26.5 86 41 50 U. 22.2 Aug. 8. 2 10 16 32. 66 50 50 U. 6 18 16.6 Adopted index cor. + 54". 17 51.5 66 21 40 U. 17.5 /i. m. 8. MI fi u 65 54 40 U. 20. 1 Mean '. 6 18 17.5 A*7 U. O 20 49. 5 65 15 25 u' 16 6 Eq time 5 18. 3 22 o!s 64 55 u! ie!i Mean time error ... 6 12 59. 2 23 48.5 63 5 55 L. 17.0 24 57.0 62 40 55 L. 17.7 25 50. 62 21 5 L. 17.8 26 49.5 61 59 10 L. 18.0 27 49.7 61 36 40 L. 18.0 OBSERVATIONS OF THE ECLIPSE OP AUGUST 7, 1869. 13 E. Times of jiltftxt'x ili'ilmnl J'nun ulixir rut ions, and compari'il ir'itli the tabular times. From the preceding exhibit (D) it will be seeu that the general rate of the chronometer is about (i iS .s per day, losing. Also, there are two days on which altitudes were observed both iu the fore- noou and afternoon, namely, August 4 and August 8. Correcting the observed errors for rate of the chronometer, it seems the forenoon errors exceed the'afternoon errors by the following amounts : 8. August 4, 2.3 8, 2.1 Mean 2.2 This difference probably arises from eccentricity of the sextant, leading to the observed alti- tudes being constantly too great. In the absence of any certain knowledge of its law we shall divide the effect equally between the observed errors by applying I'M to the forenoon errors and + 1.M to the afternoon errors to obtain the concluded error. Thus the following errors are obtained : 7l. m. K. August 4.0, G 1.3 3.6 6.9, 0.9 8.0, 0.4 They give for the error on local time on the afternoon and evening of August 8 : G" 13"' s . 7. The error of the chronometer on Washington time may be obtained with great precision from the data in Kxhibits B and ('. From .15 we find, knowing the longitude to be about I 1 ' G 1 " 17 s , and the Washington clock to be 27 s fast of sidereal time : /i. m. s. It. HI. s. 2 30 chron. = 18 30 17, Kessels clock. = 18 29 49.8, Washington sidereal time. = 10 2 15.8, Washington mean time. Whence chronometer fast of Washington time: .V' G 1 " 44".2. Again, from C we find /i. in. s. It. in. s. 3 9 chrou. = 19 9 23.8, Kessels clock. = 19 8 56.6, Washington sidereal time. = 10 2 16.2, Washington mean time. Whence chronometer fast of Washington time: 5" G"' 43 S .8. The difference of O s .4 or 8 .43 when the second decimal of seconds is included, is attributable to the time of transmission of the galvanic current through two thousand four hundred miles of wire, to armature time, and personal error of the observer in sending signal. The concluded error of chronometer on Washington mean time is therefore, 5" G m 44 8 .0. Comparing this result with the error of chronometer on local time, we have for the longitude of Des Moines Court-house : I 1 ' G m 1G S .7. . The, definitive error on local lime will be obtained by applying to the Washington time the longitude resulting from the combination of my own determinations with those of Professor I lark- ness. The geodetic difference of longitude between the Court-house and Professor Harkness's observatory is O s .7.* The longitude of the latter, resulting from his observations, being I' 1 G'" I 6 s . I . gives for that of the Court-house I 1 ' G 1 " 1G S .8. This result is the mean of five observations. This * It may be deduced from the <lat:i of these reports that from the comparison of chronometers, made on August 4, will result the difference 0".6. 14 REPORT OF PROFESSOR KEWCOMB. differs only O s .l from my single determination on August 7, and will therefore be adopted. We have, therefore, for the error of chronometer in local time : 6 1 ' 13'" 8 .8. Applying these corrections to the observed times of the three phases, we have the following results, which are compared with those computed from the data of the American Ephemeris : Local time. Washington time. Ccllnp. time. Error of (allies. Error in arc. It. III. 8. 7i. m. H, . 8, ii First contact . . . 3 43 -2. 1 4 49 1'J. 5 7.0 ]>..-> 6.0 End of totality . . 4 48 25.2 5 54 2.0 31.6 10. 1 5.4 Last contact . 5 45 23.7 6 51 40.5 32.7 7.8 4.4 Besides these phases we have two measured chords, oue just after the beginning of the eclipse, the other just before the end. The observations may be expressed as follows: at 10 b l m 31 s chro- nometer, the length of the chord was equal to the space passed over by the sun by its diurnal motion in 54 8 .55. At [ll h ] [57 m ] 23 8 it was equal to the space passed over in 27 S .15. These observations were reduced in the following way : represent by s the half-length of the measured chord, put r and r' for the apparent semi-diameters of the sun and moon as seen by the observer, and D for the apparent distance of their centers. Then D = Vr^^f z + Vr'* s 2 or, if we put * sm a = - r sin a'= r' we have D = ' COS a -4- r' COS a' This is the distance deduced from observations. The distance was calculated from the tables for the same absolute time by applying the parallax in right ascension and declination to the geo- metric co-ordinates. Thus was found Greenwich Observed Tabular Krriir of time. distance. distance. tables. 7i. m. s. / // / // // 9 57 19.0 . 32 23.3 . 10 2 59.0 29 37.3 29 39.3 + 2.0 11 58 51.0 31 38. 3 31 47. \ + 8.8 The two errors ought to have opposite signs, so that there is a discrepancy of nearly 11" in the results. There appears, therefore, to be some abnormal error in the data which 1 cannot account for, as the observations were carefully made, and seemed to me. very reliable. No correction has been applied for the effect of refraction. At the actual altitudes of the sun it would be quite small. and would tend to increase the discrepancy. The first of the above times is that of the first contact as computed from the data of the Amer- ican Ephemeris. The distance of centers was computed to see whether it would agree with the sum of the semi-diameters. The difference is 0".3. Using only contacts, and neglecting the effect of the possible error of the moon's latitude, which is probably small, we have the following results for the relative errors of the lunar and solar tables : Peirce's 3) Hansen's too great by 5".3. Hanseu's 3> Le terrier's too great by 2". 7. OBSERVATIONS OF THE ECLIPSE OP AUGUST 7, 1869. 15 The last result is deduced from the fact that in the British Nautical Almanac the moon's longi- tude is l".fl less, and (lie sun's 1".0 greater than in the American Ephemeris: F. Obtterrtttionx oftlic <litrli<i of totality and of other phenomena made by amateur observers. Most of these observations were made iu pursuance of a request accompanying a circular of instructions of which the, following is a copy : IXSTIUX TIOXS mi! mi: OHSFU\ \TION OF THE TOTAL ECLIPSE OF AUGUST 7, 1869, HY OBSEHVEKS WITHOUT TELESCOPES NEAR THE LIMITS OF TOTALITY. The following information is desired by the United States Naval Observatory, namely: The duration of total eclipse at raritiH* jilitn 1 * iiliinii tlie liuf of totality, situated between one and ten miles from its limit*. To obtain this information the observatory invites the co-operation of intelligent citizeus residing near the limits, and the following instructions are prepared tor the use of those who will co-operate: Imtti'iiments. The only indispensable instrument is a good watch, provided with asecond hand, and having a white face. The minute hand should be carefully set, so as to_be on an exact minute when the second hand is at GO". This being done it is no matter how tar wrong the watch may be. A good auxiliary w ill be a common spy-glass lashed to a round post, so as to be steady enough to give an easy view of the sun. To lessen the brilliancy of the sun, cover the object-glass witli a cap having a round hole, three-fourths of an inch iu diameter, cut in its centre. The spy-glass will be worse than useless unless one is accustomed to its use, and has it fastened so as to be steady. A smoked glass should also be prepared, but a part ol' the. glass should be very lightly smoked. .tmoigrincnls fur iilm-i-ratimi. Each observation should be made by a party of three persons. Only one instrument of each kind, watch, glass, Ac., is needed by a party. A station should be selected where they win be free from all interruption, either in the open air or at an open window facing west. One, at least, of the party must have a pencil and note-book in baud to record the time. The obserratiou. When the visible part of the sun is reduced to the narrowest crescent, the holder of the watch, keeping his eye on the face, will begin to count the seconds aloud ;* the holder of the smoked glass, with or without the spy-glass, will watch for the hist ray of true sunlight, being careful to look through the brightest part of the glass the eye will bear without inconvenience ; and the third observer, if there be one, will look for the disappearance of sunlight with the naked eye, and stand ready with pencil and paper to record the time. When the last speck of the sun has disappeared, the. observer with the glass will call "time," and the exact second at which the call was given must be immediately written down. The minute, also, must be carefully noted and recorded. The observers will then await the return of sunlight, the count of the seconds being kept up, if the face of the watch can be seen, which it probably can if held so that the light of the "corona" shall fall upon it. The duration of total eclipse will generally fall between ball' a minute and a minute and a half, depending on the position of the observer. The first Hash of true sunlight will seem to burst out suddenly, and the minute and second of its appearance must be recorded with the same care as the lime of disappearance. The difference of the two times gives the duration of totality. XlH-riiil iireciiiiliiin*. Iii .judging the beginning of totality, there is danger of error from two sources. The first is that the sun's crescent may become so narrow as to become invisible through the smoked glass, if it be too dark, several seconds before it is really all covered, and thus the observer may call "time" too soon. Such a mistake maybe detected and corrected by the (bird observer looking on with the naked eye, if the following circumstance be attended to : Tin lii'i/iiiniiiii <>f total eclipse in marked Iii/ a i'<ry rapid increase in the darkness, caused ly the advent of lite, moon's shadow. If, then, the darkness increases more rapidly after '-time" is called than it did before, time was called too soon, and must be repeated. The other danger is of the opposite kind, and should be equally avoided. It is that the light of the brilliant rose- colored protuberances which surround the dark body of the moon during the total eclipse may be mistaken for sunlight, and thus the critical moment be suffered to pass. In this case each observer must determine separately as to the exact second at which it ceased to grow darker, and if they agree within one or two seconds, the time thus judged may be supposed correct, and each one's estimate may be written down separately. The observer with the smoked glass will be most liable to the first of these mistakes ; the naked-eye observer to the last. The return of sunlight will also be preceded by a reddish glow on the border of the dark moon, which must not be mistaken for the sun. Indeed, if the observers be near the edge of the shadow, it is probable that this red glow, which comes from the hydrogen atmosphere of the sun, may bo visible during the whole time of totality. All the recorded times, with an estimate of the uncertainties to which the observers think they were liable, and a statement of the place where made, giving distance in miles and direction from the court-house, if it be a county town, and from the railroad station, if a railroad pass through, should be immediately certified by the signatures of all three observers, and forwarded to the Naval Observatory, Washington. It is particularly requested that each party send oft" its report before comparing notes with any other party ; also, that the original pencil record, however imperfect, accompany the report. All will be carefully preserved in the archives of the observatory for the use of astronomers. Statements of which the following are abstracts were received in reply to the circular. In * It would be well for the observers of each party to practice beforehand the counting, calling, and recording. 16 REPORT OF PROFESSOR NEWCOMB. explanation of these it is to be remarked that many of the positions are referred to the public land surveys, which afford the means of determining the geodetic difference of longitude between any two points nearly east and west of each other, and the difference of latitude between points north and south of each other, with considerable precision. The longitudes and latitudes of some points in Iowa have been determined from Colton's large sectional map of that State. The positions of Des Moines, Hock Island, and other stat ions, are as follows : Position 011 map. Known positions. Corrections. ,, . . # % A t A o / O ' t , DesMoiiies, (C. H.) . 41 35.0 16 40.3 41 35.0 1C 34. 2 0.0 - 6.1 Rock Island . . . 41 29.8 is 37. 9 41 30.6 16 31. H + 0. H - 6.1 Marion 42 1. 5 14 39.6 Mechanicsville . . 41 53.0 14 12.8 Red Oak .... 41 ,11.0 14 12.8 The adopted positions of the last three places are found by applying the systematic corrections thus deduced. In Illinois the same method could not be applied owing to the enormous errors with which the degrees of longitude are affected on Colton's map. The positions of a few points near Rock Island are, however, fixed by measurement along the lines of the public surveys as laid down on the map. The adopted position of llock Island is from Colonel Graham's report of 1859. When the letters S. H. follow the names of the observers, it indicates that they seem to be signed in the same handwriting. The word "Original" signifies that the original pencil record of the observations was forwarded, and that the limes given are an exact transcript therefrom. I. OBSERVATIONS NEAR THE NORTHERN LIMIT. MARION, IOWA. Latitude 42 2'.1; longitude 11 33'.5. First station. Court-house cupola, 22i chains south, and 2i chains east of the comers of town- ships 83 and 84, range and 7 west, 5 p. m. Observers. G. A. Gray, county surveyor; J. W. McClellan, ,T. G. Hayzlett. Instrument. Engineer's transit, ap. 1 J inch ; power 20. Beginning of eclipse Beginning of totality End of totality End of eclipse Duration of totality Error of watch not given, and probably unknown. ) m. s. 3 4G 50 4 48 15 4 49 18 ^ Original. 5 45 7 1 3 Observations of meteoric appearances, and of contact with spots, accompany the report. Observers express confidence in the precision of their observations. Second xtiition. One-sixteenth mile north of court-house, and one-fourth mile north of depot. Observers. E. M. Smith, M. D., Samuel W. Durham, J. W. McElhenny. h. m. n. Total phase " on," (naked eye) 4 53 4 ~) Total phase " on," called 4 53 5 > Original. Total phase " off " - 4 54 19) Obseivers think the time called was one second " slow," and so give the duration l m l.V. Third station. Near northwest corner of township 83, range 6 west. 5 p. m. Observers. E. L. Samson, James B. Graves, George W. Holmes. Instruments. Field-glass, smoked glass, four-second watch. OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1809. 17 Ml. 55 57 1 52 11 19 Original, but the last sec- onds are changed from 15 to 11. Commencement of total eclipse - 4 End of total eclipse 4 Duration of totality >l We think our observations are very nearly correct." MEOHANTCSVILLE, IOWA. Latitude 41 53'.6 ; longitude 14 6'.7. Station. Eighty-five rods northwest from Chicago and Northwestern railroad depot. Observer*. Homer S. Bradshaw, John F. Golding, P. E. Bradshaw. S. H. Original. Time called by both observers Time called by naked-eye observer Duration of totality KED OAK, IOWA. Latitude 41 51'.5 ; longitude 14 6'.7. Station. Section 1, township 81 north, range 3 west of 5th P. M., two miles due south of Stan- wood, O7i Chicago and Northwestern railroad. Observers. Samuel Yule, (with spy-glass,) E. B. Cousins, (naked eye,) G. F. McClelland, (smoked glass,) M. L. Simmons, (watch.) 7i. Beginning of totality, spy-glass 4 Beginning of totality, naked eye 4 Beginning of totality, smoked glass - 4 End of totality, spy-glass 4 End of totality, naked eye 4 End of totality, smoked glass 4 Duration of totality BOCK ISLAND, ILL Latitude 41 31'.5 ; longitude 13 31'.5. First station. Near United States arsenal, on the west end of Eock Island. Observations made by two parties are communicated by Brevet Brigadier General T. J. Bod- man, United States Army. 0&se>TtT.v. Captain and Brevet Major F. H. Parker, Captain Clifton Comly, Lieutenant Henry Metcalf, all of the Ordnance Department, United States Army. Instruments. Watch and smoked glasses. in. 50 no 50 51 51 51 1 44 43 42 48 47 46 4 3 Original. in. 58 1 57 1 48 3 20 33 17 Original. First contact 3 All obscure 5 First light 5 Last contact - 5 Duration of total phase Watch 9 s fast. Three other times of last contact were recorded, beginning at 5 1 ' 55 40 s , which the observers attributed to the fatigue of their eyes. They agree that the latest recorded time was the true one. Observers. Captain Morris Schaff, Brevet Captain M. S. Poland, and Lieutenant W. P. Butler, Ordnance Department, United States Army. Instruments. Not stated. By telescope. By the eye. /I. Ml. H. A. TO. S. Meau solar local time of beginning of eclipse . 3 58 29 3 58 29 Mean solar local time of beginning of totality 4 59 47 4 59 44 Meau solar local time of ending of totality 514 5 1 4 Mean solar local time of ending of eclipse . . . 5 57 7 ' 5 57 7 Duration of totality 1 17 1 20 3 18 REPORT OF PROFESSOR NEWCOMB. Second station. Near court-house, on fractional quarter section 35 of township 18 north of base- Hue, and range 2 west of 4th P. M. Observers. Marcus B. Osborn, John E. Humes, John F. Corker. (The results of the observations are withheld for explanations from the observers.) COLONA, ILL. Latitude 41 29'.S; longitude 13 IX'.O. Station. House of Mr. Bell, one-third mile northwest of the 13th mile-post east from Rock Island, on the Chicago, Rock Island and Pacific railroad, and at the northwest corner of northeast quarter of section 11, township 17 north, range 1 east. Observers. Mr. and Mrs. James Bell, Rev. and Mrs. S. H. \Veed. Instruments. Elgin watch, and smoked glass. Duration of total phase, 0'" 59 s (17 m 35 s 1G"> 30 s .) Original record not sent, but the description of the observations and phenomena is sufficiently minute, precise, and satisfactory to inspire confidence in the observations. GENESEO, ILL. Latitude 41 27'.4 ; longitude 13 G'.4. First station.* One hundred feet south of passenger depot of Chicago, Rock Island and Pacific railroad. Observers. L. C. Campbell, notary public; J. F. Dresser, banker; John Reiter, dentist; C. E. Parker, merchant; F. Stein, jeweler. ll. II). S. First appearance - 4 6 00 "J Commencement of totality 5 8 23 Close of totality 5 8 56J Disappeared (5 5 30 .Duration of totality 33J Original. Second station. About four miles south of Geneseo; or, accurately, the northwest corner of section 8, township 1C north, range 3 east of 4th P. M. Latitude 41 24'.i; longitude 13 S'.O. Observers. E. C. Moderwell, W. C. Brown, M. 1)., John Smith. Duration of totality, 5S S 2 s (2' 29 s ) 1"' 31 s . Original record not forwarded. LACON, ILL. Doctor and Mrs. George Davis give a duration of 2 minutes seconds, but are iiot certain of its correctness. It must be incorrect, as Lacon is very nearly on the limit. CHKNOA, ILL. Station. Near southeast corner of section 2, township 2fi, range 4. Observers. C. S. Elder, M. D. (The others have not signed.) Duration of totality, .">9.J- S ll s = 48i s . (Original.) EL PA.SO, ILL. Station. 1,!S5 feet east and 41G feet north from railroad station. Observers. Joseph 11. Moore, W. R. Torrey, G. L. Gibson. Instruments. Watch, smoked glass, and achromatic telescope lashed firmly to a round post. /). Ml. 8. Beginning of eclipse 4 10 30 ^j Beginning of totality - - - 5 10 30 [ Knd of totality 5 12 28 f Chlca S *''' End of eclipse 9 30 J Original record not forwarded. GRIDLEY, ILL. Station. One-half mile north of station-house, and in the center of section 4, township 2G north, range 3 east of 3d P. M. Observers. Two parties of three in each. Observations communicated by W. II. Boris, who says the two parties agreed perfectly, so they deem it unnecessary to send separate reports. Duration of totality, 5 h I" 1 5 s 5 h = l 5 s . Original record not forwarded. * The next party refer to this station, and give its position as near center of section 21, township 17 north, range 3 east of 4th P. M. The longitude and latitude have been deduced from this statement. OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 19 PAXTON, ILL. First station. One thousand feet south 15 east from court-house. Observers. II. J. Howe and W. H. Pells, observers ; E. T. Glasener, time-counter ; John M. Ilanley and Lewis K. Jones, tally-keepers. Duration of totality, 20' 30 s 20 2 s = 28 s . (Original.) Second station. Three-fourths mile southeast of court-house. Obsen-ers. Professor T. N. Hasselquist, A. E. Corwin, Rev. J. S. Harkey, - , stu- dent. (S. H.) DANVILLE, ILL. First station. Three-fourths mile southeast of court-house. Observers. Warren Dunbar, (eye,) J. G. English, (time,) J. C. Winslow, (glass.) /I. HI. 8. Time of beginning -- 4 14 15 J Time of beginning of totality 5 13 Time of end of totality - 5 14 6 Time of eud of eel i] isc 6 5 20 } Apparently original. Naked eye Time of beginning 5 12 54 Time of ending 5 14 6 3 All these agree that the naked eye observer called "time" too soon, so that the duration of totality was I 1 " (i s . t Second station. Near center of section 8, township 19 north, range 11 west of 2d P. M. Observers. VV. T. Cunningham, Win. P. Chandler, Theo. Lemon. h. m. 8. Eclipse commenced 4 15 30 ) Time called for 5 16 10 ! Q Time called for second time 5 17 21 | Duration of total phase 1 11 J COLUMBUS, IND. First station. Two and three-fourths miles west of Columbus. Observers. Rev. N. S. Dickey, L. VV. Comstock, Albert T. Beck. Duration of totality, l m 4 s . (No original record.) Second station. Not given. Observer. Doctor (leo. <i. Rabb. Duration of totality, I" 1 .'!0 S . (No original record.) Third station. One mile north of court-house. Observer. Professor A. H. Graham. Duration of totality, l m 19 s . (No original record.) FRANKLIN, IND. Station. Near court-house. Observers. Ke\ '. J. B. Morey, Professor F. W. Brown, Professor J. S. Houghain, W. T. Stott. h. in. s. Beginning 5 25 58 First call 2 9 too soon. 5 26 True call. Kuding ~> 26 37 EDINBURG, INU. station. Three hundred yards north of railroad station. Observer. Rev. John B. Logan, without'assistance. Instruments. Watch and smoked glass. /I. HI. . First appearance on northwest part of sun - 4 10 Total darkness, lasting 40 seconds 5 12 ! Qri iual recol . d . Sun began to appear ; streaks still appear ; darker than bright moonlight - 5 12 40 J 20 REPORT OF PROFESSOR NEWCOMB. MOUNT VERNON, IND. Slation. Masonic Hall. From the section lines it is deduced that the station is 1.074 statute mile east, aud 13.8 statute miles south, of a point of New Harmony, the posi- tion of which was determined by the Coast Survey in 1848, as follows: latitude, 38 7' 50"; longi- tude, 5" 51> 20 s . Observers. Aaron Baker, C. E., S. H. Pearse, M. D., S. Milner. Instrument. Engineer's transit aperture, : f in.; power, 10. It. m. *. Beginning of eclipse 4 25 27 } Beginning of total phase 5 24 7!l I Ending of total phase - 5 20 55 ( ( Ending of eclipse 21 58 I Duration of totality 1 30 CARLISLE, KY. Station. Not given. Observers. E. C. H. Willoughby, Dr. W. W. Fritts, Charles Boynton. 37 i 20 J ' Original. Totality lasted 1 43 At the beginning of obscuration one observer called " time " two seconds earlier than the other. The last call was adopted. FRANKLINTON, K. C. Station. One hundred and sixty yards west of railroad depot. Observers. George W. Neal, A. M., C. W. Conway, Calvin Pritchard, Robert N". Winston. Instruments. Spy-glass, smoked glass, and racer's watch, with long second hand. Total eclipse lasted 03 seconds, per spy-glass observer. Total eclipse lasted 01 seconds, per naked-eye observer. (No original record.) WILSON, WILSON COUNTY, N. C. Station. Not given. Observers. Jno. W. Dunham, Jno. McBride, Robert S. Husk, J. A. Fugua, Eev. A. A. Bentou. Instruments. Camera obscura and smoked glass. The original record is sent, by which it appears that the three first observers agreed upon G 1 ' 27 s as the time of beginning of total phase, and the two first each observed O 1 ' I 111 51 s as that of ending; but, in the record, the commencements by D. and H. seem to be altered to agree with McB. H. "noticed the obscuration as total in the-glass, and removed it before calling;" but no reason is given for the change of D.'s observations from 22 s to 27 s . II. STATIONS NEAR THE SOUTHERN LIMIT. HANNIBAL, Mu. First station. House of Eev. Jno. Leighton. Observers. Eev. Juo. Leighton, G. H. Shields, W. B. Fiero. The latter does not sign the report. Instrument. Thirty-inch spy-glass. /I. HI. *. Commenced, (observer with glass) 5 1 10 ") Commenced, (observer with naked eye) ' 5 1 10 I . Ended, (observer with glass) 5 3 10 i Ended, (observer with naked eye) 5 3 8 J The seconds of ending both seem to have been corrected or twice recorded. Second station. 1,208 feet north 29 west from railroad depot. Observers. H. M. Sutnner, C. E., F. B. Lockliug, C. E., E. L. Corthell, C. E., G. H. Williams. ll. III. S. Total phase begins, (through glass) 5 8 52 "| Total phase ends, (through glass) - 5 10 49 I _. f . . Total phase begins, (naked eye) 5 10 49 f Total phase ends, (naked eye) 5 10 49 J The observers give the first observation, 5'' 8 m 52 3 , as the true time of beginning. The third is probably 2'" wrong, through inadvertence in recording. OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 21 BOWLING GREEN, Mo. Fii-xt station. Court-house Observers. 3. W. Basyc, Melville Smith, Albeit Cluster, Mrs. L. E. Basyp. (S. H.) /I. 111. 8. Total eclipse begins 4 51 41 | Continued 51 j In the accompaaying report the end is given at 4 1 ' 40 32 s , and a duration of 51 seconds thence deduced. Second station. Residence of Augustus C. Sheldon, 50 rods south of court-house. Observers. Augustus C. Sheldon, Nellie H. Sheldon, W. P. Lawry. The observers sign a certificate that they made particular observation of the duration of the total eclipse, and found it to be forty-six (40) seconds. No original record forwarded. ALTON,' ILL. Station. Near quarter-section corner on the line between sections 33 and 34, township (i north, of range 10 west of 3d P. M. Observers. T. M. Long, county surveyor. Instrument. Transit compass, with telescope attached. h. )/i. Beginning of eclipse 4 1,3 Total obscuration 5 11 Return of light 5 llf Ending of eclipse 7i ~No original record forwarded. CARLYLK, ILL. Station. 1,100 feet south of west of court-house, and 1,100 feet north of west of the depot, on the Ohio and Mississippi railroad. Observers. Zophar Case, .lames Harkley, William A. Robinson. h. m. s. Commencement of obscured light of sun 4 15 3 Total obscuration 5 15 39 First sunlight 517 6 Disappearance of any obscuration of sun 11 50 Duration of totality 1 '21 No original record, but the report is duly certified. HENDERSON, KY. /Station. P>ank of Ohio River, four squares from court-house. Observers. T. H. Crosby, C. E., P..L. Blacknell, president Ghent College. (S. H.) Instrument. Engineer's transit, with telescope of 1^ inch aperture and 13 inches long. h. m. . Beginning of total eclipse 5 22 30 i End of total eclipse 5 24 I On S lual - OAKLAND STATION, KY. First station. Oakland Station, on the Louisville and Nashville rail- road, 11.3 miles north 00 east from Bowling Green. Observers. John E. Young-love, Jno. J. Ililburn, Lieutenant W. 1. Reise, C. R. Edwards. Beginning of total phase, (to. s. t. of Bowling /,. ,. 8 . Green) 5 24 30 End of total phase 5 24 33 Duration, three seconds. No original record sent. "The beginning of total phase was very accurately taken, both observers giving the same instant, but we deem it proper to acknowledge our doubt as to the exact time of ending. We had expected a total phase of some 20 or 30 seconds, and were so much surprised at the sudden reap pearance of the sun that we may have allowed the critical moment to pass unobserved." 22 REPORT OF PROFESSOR NEWCOMB. Second station. One-fourth mile southwest of Oakland Station, 11 miles from Bowling Green. Observers. J. A. Timmons, A. M.; J. L. Donaldson, A. B.; J. M. Youn glove, A. B. Instruments. Smoked glass and opera glass. Beginning of totality End of totality End of eclipse Duration of total phase, about 7l. Ml. S. .> 23 45 ") 5 23 47 fi 18 28 2 j > Original. "With the naked eye totality was iiot plainly visible; the corona appeared to be not quite perfect, and many mistook the reflection from the sun to be the sun itself, thereby causing the belief of non-totality. " The stars were plainly visible with jthe naked eye." The watch was compared with a meridian mark at Bowling Green. On the 7th it stood Ou the 8th it stood /i. m. 8. 12 5 28 12 5 19 BURKSVILLE, KY. First station. Not given. Observers. V*. G. Hunter, M. D.; J. W. Williams, clerk circuit court ; L. A. WaggeuerJ clerk county court; Scott Walker, attorney at law. Duration of total eclipse, 1"' 16 s . The original record is forwarded, but is not clear. The duration seems to have been counted from the moment of obscuration, independently of the absolute time. Second station. Not given. Observers. B. M. Alexander, with two others who do not sign the report. Total eclipse began 37 minutes past 5, and lasted 1 "' 2S S , which is considered only approxi- mately true. III. DURATIONS OBSERVED AT POINTS TOO FAR WITHIN THE SHADOW TO BE t'SED IN FIXING ITS LIMITS. These observations being valuable principally as atlbrding data for judging of the general Accuracy of extemporized observers, it is deemed unnecessary to give more than I he observed dura- tion and the name of thp person by whom it is communicated. Place. Lat. Long. Duration. Communicated by Remarks, o m. . Midway, Ky - - - - . 7 2 24 Ensign David N. Bell, U. S. N . One mile north of railroad sta- Tayloraville, N. C . . . 4 2 15 A. C. bo.vd <! nl. tion. 3 i 17 J. A. McDonald i'l nl. Davidson College . . . 3 2 8 Professor!'. Phillips - Two other observations gave River View . . 3 2 20 M. I!ald\vin 1 1 nl. 2 fl 8 and 2 m 10 B , of which the :', 2 25 .John A. Raiiisrv. lirst is doubtful. 3 2 35 \V. 11. 1,'obbins. 3 2 13 F. C. Robbins. Chanel Hill .... 1 2 5 James J!. Mason (/ ul. Kalcigh - - 1 1 58 'William Primrose </ ill. . . Mean of two observations. REPORT PROCESSOR WILLIAM HAROESS, U. S REPORT OF PROFESSOR WILLIAM BARENESS, U. S. N. UNITED STATES NAVAL OBSERVATORY, Washington, October 1, 18G9. SIR : I have the honor to submit the following report in relation to the astronomical and spec- troscopic observations made by me in connection with the expedition sent out to Iowa, by this Observatory, for the purpose of observing the total solar eclipse of the 7th of August last. INTRODUCTORY. Onr instruments and apparatus were delivered to Adams Express Company on Saturday, July ;?, to be forwarded to Des Moines, in the State of Iowa ; and the party left Washington on the even- ing of the following Monday. At that time, owing to the absence, of any exact determination of the positions of the towns and villages near t he ecu I nil line of the eclipse, we had not decided defi- nitely what station we would occupy, but it seemed probable that the most favorable point would be Mitchellville, a small village, situated on the Chicago, Rock Island and Pacific railroad, whose bear- ing from Des Moines is north 05 east, and its distance 13.2 miles. About noon on Saturday, July 10, we reached Des Moines, and upon going to the, hotel I met Mr. E. P. Austin, of the Unite*? States Coast Survey, who was engaged in obtaining the geographical position of the city. His observations were not then finished, but they showed that it was not more than eleven or twelve miles to the southwest of the central line of the eclipse. The duration of the totality there would, therefore, be less than two seconds shorter than on the central line itself, and as a city of sixteen thousand inhabitants necessarily offered many facilities which we could not expect in a small vil- lage, we at once decided to remain in Des Moines. SITE OF TEMPORARY OBSERVATORY. Saturday afternoon and the following Monday were spent in selecting a site for our observa- tory, and as we were to the southwest of the central line of the eclipse we confined our reconnais- sance to the northeastern part of the city. The spot which seemed, in all respects, the most desir- able is situated on the northwest corner of Second and Short streets. It is a high piece of vacant ground on the west bank of the Des Moines River, with a horizon almost entirely devoid of obstruc- tions, and, as the city is not built up so far north, there is no travel, and it is perfectly free from that great enemy of photography, dust. There is also a well of water near, which we thought A decided advantage, but upon trial, afterwards, it proved to be useless for photographic purposes. I ascertained that this land belonged to Mrs. Sytha .1. Hall, and thai her agent in the city was Mr. J. M. Ballinger. On Tuesday morning I called upon him and, after stating the case to him, he said that he was sure Mrs. Hall would be very glad to have us place our observatory there, and we had his permission to do so. No charge was made for the use of the land, and our thanks are due to him and Mrs. Hall for their kindness in the matter. THE TEMPORARY OBSERVATORY. On the afternoon of July 13 I called upon Mr. F. T. Nelson, a builder whom I can confidently recommend, and made arrangements with him to erect our temporary observatory. He set some of his men to work at it next morning, intending to have it finished in two or three days, but before noon the weather changed and a series of thunder-storms set in which lasted, -with short intermix 4* 26 REPORT OF PROFESSOR ITARKNESS. sions, lor the next five days. The men managed to do some work between the storms, but their progress \v;is necessarily slow, and it was the afternoon of July 20 before the building was finished. As soon as the carpenters were done we sent to the express office for our instruments and appa- ratus, and by six o'clock that evening the boxes containing them were all safely stored in the observatory. Plate I is a general view of the building from a photograph by Mr. E. J. Ward, and Plate II is a plan of it drawn to a scale of one-quarter of an inch to a foot. It was thirty-two feet long by sixteen feet wide, constructed of rough pine boards, and so placed that Ihe ridge of its roof ran almost exactly north and south ; the longest sides of the building facing respectively to the east and west. The eaves of the roof were 8.5 feet above the ground, and the boarding on the sides of the building was horizontal, that on the east side being continued quite up to the roof, while that on the west side was only carried to the height of five feet above the ground, except for a space of seven feet at the north end of the building, where it was carried quite up to the roof. This space, seven feet in length and sixteen feet in width, was partitioned off and inclosed as a dark room for photographic purposes. A complete description of it, and all its arrangements, will be found in Dr. Curtis's report. The seven and three-quarter inch telescope was mounted exactly in the cen- tral line of the building, that is, eight feet from either side, and, in order to permit its use from the western horizon quite up to the zenith, the ridge of the roof, which was sixteen feet above the ground, was placed two feet to the east of the central line. All the space on the east side of the ridge pole, and eight feet of the north end of that on the west side, (sufficient to cover the photo- graphic dark room,) was roofed over with boards. The remaining space, twenty five feet in length, on the west side of the ridge pole, was covered with canvas (furnished by the United States Arm\ Medical Museum) which, at the cave, passed over a movable horizontal rail, and thence down to the board side of the building, which, as before stated, was here only five feet high. When the telescopes were in use this canvas roof was rolled up like an awning, and the horizontal rail was removed, thus affording a perfectly unobstructed view of all that portion of the heavens traversed by the sun between noon and sunset. The north and south ends of the building were covered with boards placed vertically, and the door for entrance was situated in the south end. Suitable open- ings for ventilation were placed in the gables near the roof. With the exception of those in t lie- dark room, there were no windows, the light coming in through the canvas roof being sufficient for all purposes. The ground upon which the observatory stood is clay, and as it is well known that clay sprin- kled with powdered lime soon produces a very hard surface, I thought that a sufficiently durable floor might be obtained in that way. Upon trial, however, it was found that the constant walking on it gave rise to such a quantity of dust as would have rendered it utterly impossible to take good photographs, and J was obliged to have a floor of planed boards put down. Owing to the irregu- larity of the^round the southern part of this floor was laid five and one-quarter inches higher than the northern, thus making a step between the two, as shown on the plan. By Thursday, July 22, the large telescope was mounted, and on the following day a photograph of the sun was made, and some observations for time and latitude were taken. The equatorial adjustments of the large telescope were completed on July 24, and from that time till August !) pho- tographs were taken and observations made every day when the weather pennitted. THE INSTEUMENTS EMPLOYED. An Achromatic Telescope of seven and three-quarters inches clear aperture, equatorially mounted and provided with a driving clock and divided circles, belonging to the United States Naval Acad- emy, was kindly lent to the observatory by Vice- Admiral I). I). Porter, to be used for photograph- ing the eclipse. The necessary alterations to fit it for that purpose were made under my supervision, and much credit is due to Mr. W. F. Gardner, the instrument-maker attached to the Observatory, for the interest he took in pushing the work forward to completion in the very limited time at our disposal. As this instrument was used almost solely by Dr. Curtis, it is unnecessary to enter into details respecting it here. A full description of it will be found in his report. The remaining instruments in this list are all my own private property. An Achromatic Telescope of 43.58 inches focal length, and 3.01 inches clear aperture, made by OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, ldt>9. ~27 Alvan Clark and Sons, of Cambridgport, Massachusetts. This instrument, which is a remarkably fine oiie, is provided with a terrestrial eye-piece magnifying 29.1 diameters, and with Huygenian eye-pieces magnifying respectively 34.5, 05.5, and l.Ti.4 diameters. It is equatorially mounted on a very firm, portable tripod stand, which can be adjusted to any latitude, except very low ones, and has a slow motion by which it may be moved through a few degrees in azimuth. The polar and declination axes are both provided with clamp screws, but there are neither divided circles nor tan- gent screws. Its finder has a focal length of <S.O!I inches, and a clear aperture of 0.08 inches, and is provided with two eye-pieces: a direct one magnifying 10.0 diameters, and a diagonal one magnifying 0.2 diameters. Each of these eye-pieces has a Held of view 3 20' in diameter. The finder is firmly fastened to the telescope tube, and is not capable of any adjustment whatever. It originally car- ried in its field of view a pair of thick cross-wires, whose position was so near correct that when a star was brought to their intersection it was always visible in the field of view of the telescope, even with the highest eye-piece. When I decided to use the telescope for spectroscopic work, it became necessary to have more delicate means of pointing. I therefore had the thick cross- wires removed, and a common sewing needle, whose point can be placed and fastened in any part of the field of view, inserted in their place. It is easily adjusted, and has proved very satisfactory ; the image of the object to be observed being readily brought upon the slit of the spectroscope by bringing its image in the finder just into contact with the point of the needle. A Sinr/lc-prixm ttyectroscope. This instrument was originally made by P. Desaga, of Heidelberg, and was intended to be used only for chemical purposes, but J have had great alterations and addi- tions made in almost all its details, so that it can now be employed with equal facility for either chemical or astronomical purposes. It is shown, arranged for astronomical observation and attached to the telescope, in Plate IV. It consists of a central brass box, which contains the prism, and from which radiate three tubes of unequal sizes. In order to connect the instrument to the telescope, the end of the largest of these tubes is slipped into an adapter, and fastened there by means of a clamp screw, not shown in the plate. Inside of, and concentric with, this large tube is a smaller one, carrying at the end which terminates in the prism box an achromatic collimating leus, and at its other extremity, in the principal focus of the collimating lens, a slit, the width of which can be varied at pleasure by means of a screw motion. The principle upon which this slit is constructed will be easily understood by examining the diagram, Fig. 1, where a and b are Fig. 1. the two jaws of the slit, which are constantly pressed together by the springs shown at their ends ; c is-a wedge-shaped piece of brass, lying above the jaws, and having a rectangular opening in its center to permit the light to pass to them. This wedge can be -moved lengthwise by means of a screw; and two pins, one inserted in each jaw, rest against its sides. When the wedge is moved downward it presses against these pins and causes the jaws to open ; when it is moved upward it releases the pins and the springs press the jaws closer together. The jaws always open or close equally on each side of the slit, so that the position of the middle point bet ween them is constant. This is a matter of some importance, because generally the thickness of a line in the spectrum is precisely equal to the angular opening of the slit, and if the slit were to open from one side only, the lines in the spectrum would widen upon one side only, thus shifting the absolute position of their centers. Another of the tubes radiating from the prism box is a small achromatic telescope, the eye-piece of which is provided with a number of shade glasses of different colors, any one of which may be used to protect the eye when viewing the solar spectrum. The remaining tube which radiates from the prism box contains, at the end which terminates in the box, an achromatic collimatiug lens, and at its other end, in the principal focus of the collimating lens, a very finely graduated photographed scale of equal parts. The action of the instrument is as follows: Having been attached to the sliding tube at the eye end of the forty-three inch telescope, that tube is moved out or in, by means of its rack work, until the slit of the spectroscope is placed precisely in the principal focus of the object glass. Then the sliding tube is firmly clamped, and the telescope being directed to any object, the spectrum of which it is desired to examine, the image of that object is made to fall within the jaws of the slit. The rays of light, after passing through the slit, fall upon its collimatiug lens and are rendered per- fectly parallel. Then impinging upon the prism, they sutler refraction and dispersion in their pas- 2B REPORT OF PROFESSOR HARKNESS. sage through it, and finally, reaching the object glass of the small telescope, the ra,vs of each degree of refrangibility are brought to a separate focus by it, and arc seen spread out into a spectrum when viewed through its eye-piece. The rays of light proceeding from the photographed scale are ren dered parallel by its colliinating lens; then falling upon the second face of the prism, are reflected from it to the object glass of the small telescope, and, passing through it, are brought to a focus and form an image of the scale precisely at the. same spot where the rays from the slit form the spectrum. Therefore, on looking into the small telescope the spectrum and the scale are seen together, and it serves as a micrometer to measure the position of the lines in the spectrum. The scale is furnished with an adjusting screw, by means of which its fiftieth division can be made to coincide accurately with the sodium line. How to illuminate the scale properly in all posi- tions of the large telescope was a problem which cost me much thought, but I finally succeeded in devising the following arrangement, which has proved quite satisfactory : The tube which carries the scale and its collimating lens is embraced by a clamp, which can be fixed in any required posi- tion, and from which extends a long curved arm projecting some distance beyond the plane .of the scale. At the end of this arm is a brass ball pierced with a socket, the produced axis of which passes through, and is at right angles to, the produced axis of the tube which carries the scale and its collimating lens. Tn this socket is an axis which carries a bent arm, in one extremity of which a lantern swings suspended between two points, and in the other extremity a rod (which is in the produced axis of the socket in the ball) slides back and forward, carrying at its end a reflector inclined at an angle of forty : five degrees to the rod. Now, let the position of the spectroscope be what it will, the clamp can be loosened and turned on the lube which carries the scale until the axis of the socket in the ball is horizontal. Then the lantern can be placed vertically by moving it on its pivots, and, if necessary, turning in its socket the axis which carries the bent arm. Such being the state of affairs, the light from the lantern will intersect, at right angles, the produced axis of the tube which carries the scale, and by placing the inclined reflector in the proper position it will be thrown directly down that tube, and on looking into the small telescope the scale will be seen properly illuminated. The lantern itself is of the form devised by 3Ir. Joseph A. Rogers, of the Hydrographic Office, and is fitted to burn a fluid composed of four volumes of alcohol mixed with one volume of spirits of turpentine. The adapter, by which the spectroscope is attached to the telescope, has a motion of revolution around its axis, by means of which the slit of the spectroscope can be placed at any desired angle with a circle of right ascension, and then it can be firmly fixed there by a clamp-scre\v which is pro- vided for that purpose. There is also a hole in the side of the adapter which permits light to fall on a small equilateral prism placed over one half the length of the slit of the spectroscope, thus fur- nishing the means of comparing the spectrum of the object to which the telescope is directed with that of any known chemical element. The following are the constants relating to this instrument : Small telescope: Focal distance of object glass 6.55 inches. Clear aperture of object, glass O.Si; inch. Diameter of field of view 5 ">'' .Magnifying power 5.71 diameters. Collimating lens for slit : Focal distance ""'-' inches. Clear aperture 0.82 inch. Collimating lens for scale : Focal distance 1-'^ inches. Clear aperture 0.82 inch. Prism : Refracting angle M 8' Minimum deviation of line D 47 44' Refractive index Density - 3.532 OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 29 In order to give breadth to the spectrum of a star, there is a plano-convex cylindrical lens, 0.65 of an inch square, with ;i t'oeal length of 11.5 inches, which can be inserted in the adapter. The micrometer scale is photographed on glass in such a manner as to show bright lines on a dark ground. It has tour hundred and twenty-one divisions to an inch, whence there results as the value of a single division 0.002370 of an inch. Upon a careful examination the graduation proved to be not perfectly regular, and the follow- ing table is therefore inserted, which gives the distance from the zero point to each tenth division, as determined from measures made with the mural circle: Division. Angular distant r. 1 Division. Angular distance. o , o / // 110 3 35 32 10 19 30 120 3 55 10 20 39 13 130 : 4 14 42 30 58 48 140 4 34 25 40 1 18 20 150 4 53 59 50 1 3? 15 160 5 13 21 60 1 57 '.'7 170 5 32 51 70 2 HI .->:; 180 5 52 28 80 2 36 17 190 6 11 56 90 2 55 55 200 6 31 19 100 3 lo :'.() The mean value of one division is, therefore, 1' 57" A and the corrections necessary to free the scale from the effect of irregularity of division are as follows: Division. Correction. Division. Correction. Division. Correct ion. H II 70 + 5 140 - 29 10 + 4 80 + 15 150 - 29 20 5 90 + H 160 - 17 so 6 100 + 4 170 - 13 40 - 4 110 - 18 180 - 16 50 + 5 120 22 190 - 10 60 3 130 20 200 + 1 In order to render the scale of this instrument comparable with those of others, we have the data contained in the following table, the first column of which gives the designation of the line in the spectrum ; the second column the scale-reading of this instrument; the third column the read- ing of Kirchhoff's scale; and the fourth column the wave length expressed in millionth a of a mil- limeter. The readings given for the line D correspond to the mean of the two sodium lines, and those given for 6 correspond to the mean of the three magnesium lines, giving double weight to the least refrangible line. Beyond the line G- the readings given in the column belonging to Kirch- hoff's scale are those of Angstrom's and Thalen's continuation of Kirchhoff's map : Lino. Scalr II. Si-ale K. Wave trust li. Line. Scale H. Seal,: K. \\"n\e length. a 26.9 503 1> 71.5 1643 518.1 B 31.5 sea 687.5 F 84.8 2080 4*6. :, C 36.2 694 656. 8 G 117.8 2855 431.0 D 50.0 1005 589.7 H, 146.5 8778 397.2 E 67. 9 1524 527.4 H, 150.5 3882 393. (i 30 REPORT OF PROFESSOR HARKNF.SS. By means of a graphical interpolation I have obtained from these data the reading of Kirch - hoif's scale, and the wave length, for every fifth division of the scale of my instrument, as given in the following table : Scale H. Scale K. Wave length. Scale H. Scale K. Wave length. 25 462 . 95 2335 467. 2 30 560 700.0 100 2445 168,3 35 665 664.2 105 2560 449.9 40 772 636.2 110 2675 442. 1 -45 885 611.8 115 2788 l:;i. - 50 1005 589.8 120 2925 428.0 55 1135 569.8 125 3095 i2i.; 60 1278 551.8 130 3262 415. r> 65 1432 535.8 135 :; 1 K 409. 7 70 1595 521. 4 140 3590 404.2 75 1760 508.5 145 3735 399.0 80 1920 497.0 150 3868 394.1 85 20&5 486.5 166 3896 389.5. 90 2218 476.6 Under favorable conditions this spectroscope will show the line I) in the solar spectrum dis- tinctly double. An Arago Polar iscope, consisting of a plate of quartz cut perpendicularly to the axis, and a double-image prism, giving images of complementary colors when polarized light is present. A Savart Polariscope, consisting of a plate of quartz cut obliquely to the axis, and a plate of tourmaline, giving Savart's bands when polarized light is present. A Sextant, made by Stackpole& Brother, of New York, from my own designs, marked No. 937, of six inches radius, divided on platina, and reading to ten seconds, having a telescope of 5.32 inches focus and 0.89 inch clear aperture, provided with eye-pieces magnifying respectively 2.75, 5.66, and 8.88 diameters. Attached to the index bar is a finding-level, which proved a very great coin e nience and saved much time and trouble. If we let E represent the correction necessary to free any measured angle, u>, from the eft'ect of eccentricity of the sextant, and () represent the reading of the point oil the arc where the divisions of the limb and vernier coincided when the angle u> was measured, then E = 2 e . sin (<o). cos [a + (<)] and e being constants which must be determined from the measurement of known angles. The quantity a is the angle included by the two lines passing, respectively, from the center of the divided arc to the zero .point on the limb, and from the center of the divided arc to the center on which the index bar turns. For the quantity e we have 2b II. sin 1" in which b is the distance from the center of the divided arc to the center on which the index bar turns, and K is the radius of the divided arc. After my return from Ues Moines, from the measurement of seventeen known angles, included between the limits 34 22' and 112 20', I found, by the method of least squares, for the sextant under consideration = 114 4 2e= 62".5 OBSERVATIONS OF THE ECLIPSE OF AUGUST 7. 1869. 31 and by moans of the formula given above I have computed from these values the following table of the corrections which must be applied to angles measured with this instrument in order to free them from the effects of eccentricity. lit E " E 6) E II o II O II 0.0 60 + S.I 100 + 19.9 10 + 1.2 60 + 10.2 110 + 22. G 20 + 2.0 70 + 12. 5 120 + 25.3 30 + 4.3 80 ! + 14. 9 130 + 28.0 40 + (5.1 90 + 17.4 140 + 30. 8 A Mercurial Artificial ll<>r!:oit. marked Ha. 1, having a folding roof, and an iron trough, three inches wide by five inches long. If ( is the double altitude of an object seen in au artificial horizon ; /* the index of refraction of the glass composing the roof of the horizon; x a constant peculiar to the roof which is employed and which must be determined from observations made for that .purpose ; then, assuming /i = 1.514, the correction necessary to free any observed angle from the error introduced by a prismatic form of one or both of the glasses composing the roof of the horizon will be given by the expression ' ( 1 /"" sin 2 (45 --~ "cos (450 4 w ) The value of the co eflicient of /., for values of < ranging between 30 and 15(1, is given in the, following table : u u <j u o o 30 0. fi502 ISO 55 0.5559 125 35 . <;,'.->:> 145 60 .5444 120 40 . f.04l 140 70 . 5273 110 45 . 5855 135 80 . 5173 100 BO . 5C.95 130 90 . 5140 90 From three sets ;>f observations of Polaris reflected, made with the mural circle belonging to this Observatory, and the horizon Ha. 1, each set consisting of five readings of the micrometer with-the side A of the horizon roof next the observer, and live readings with the side B next the observer, I found that when the side A was next the observer the star appeared too high by the fol- lowing quantities: 0".285 .207 .21!) .Mean = 0.237 As the double altitude of Polaris at the time of observation was 80 34', the co-efficient of; was 0.5171. Hence we have: 32 REPORT OP PROFESSOR HARKNESS. The corrections to be applied to double altitudes measured with this horizon, for Tallies of between 30 and 150, are therefore as follows : tf C'orr. u u COIT. u o a ^ o // tj 30 0.30 150 70 0.24 110 40 .28 140 80 .24 100 50 .20 130 90 0.24 90 CO 0.25 120 These corrections are to be subtracted from double altitudes measured with the side A of the roof next the observer, and added to double altitudes measured with the side B next the observer. However, they will never change the resulting single altitude by more than 0".15, and, as that is a quantity utterly unappreciable with a sextant, this roof may be considered as perfect. A Pocket Sextant, made by Stackpole and Brother, of New York, marked No. .'546, having an arc of two and a quarter inches radius, and reading to single minutes. A Black Glass Artificial Horizon, four inches long by three inches wide, provided with a very sen- sitive level, and an inclined plane with black glass surfaces which can be set on the horizon for the purpose of measuring zenith distances ranging between seventy and one hundred and thirty degrees. A Prismatic Compass, having colored glasses for the purpose of observing the sun, and a needle three inches long, carrying a metal circle three inches in diameter, divided to single degrees. A Small Reflecting Lerel. A Pocket Compass. A Fifty-foot Chesterman''s Metallic Tape Measure, which had been carefully tested, by means of an eighteen-inch steel standard rule, and found to be correct. A Binocular Field Glass, magnifying 5.50 diameters and having a Held of view of 2 50'. A Pocket Achromatic Telescope, having an object glass made by Alvan Clark and Sons, of 9.99 inches focus and 1.09 inches clear aperture, with a terrestrial eye-piece magnifying 19.2 diameters and a field of view of 1 48'; provided with a screw clip for holding it steadily while observing. A Set of Three Colored Glasses, mounted in a horn frame for the pocket. A Pocket Thermometer. A Rain Gauge, having a receiving surface 2.788 inches in diameter, and a glass measure for the same, holding half an inch of rain and graduated to each 0.005 of an inch. A Break-circuit Telegraph Key. A Set of Drawing Instrument's. We had with us, for the use of the party, three mean-time box chronometers, made by T. S. and ,T. 1). Negus, of New York, a full account of which will be found in Professor Eastman's report. I had also the following articles: American Nautical Almanac, and supplement, for 1869; Chauvenet's Astronomy ; Loomis's Practical Astronomy ; Chauvenef s Trigonometry ; Four-figure Logarithms ; Bowditch's Useful Tables ; Bremiker's Six-figure Logarithms ; Crelle's Multiplication Table ; Star Maps ; scale of tints with which to compare the colors of the protuberances around the sun during the totality; blank forms for latitude and time observations; blanks for spectroscope observations. GENERAL REMARKS ON THE OBSERVATIONS FOR TIME AND LATITUDE. The observations for time and latitude were all made by me, assisted either by Professor East- man or Dr. Curtis, one of whom always noted the time at a given signal, and then recorded the observation. Under the circumstances, I considered that method as accurate, and certainly much more convenient, than it would have been for me to have taken up the beat of the chronometer and noted the time myself. The instruments employed were the sextant Stackpole and Brother, No. 937, with a magnifying power of 8.88 diameters on the telescope ; the mercurial artificial horizon Ha. 1 ; and the mean-time chronometer T. S. and J. D. Negus, No. 1319. At night the index correction of the sextant was determined by observing the coincidence of the direct and reflected image of a star; in the day-time it was determined by measuring the diameter of the sun both on and off the arc. In order to avoid reading tbe vernier backward on the arc of excess, which always involves risk 1809. 33 of error, tin- zero of Mio graduation was taken at a point live degrees oft' the are. Thus an angle recorded as 4 li.V 50" was really 34' 10" oft' the are. This applies only to angles measured on the arc of excess for the' purpose of determining index corrections. The refractions have, been computed by means of Hessel's formula, sometimes using the tallies given in the appendix to the Washington observations for 1845, and sometimes those given in Loomis's Practical Astronomy ; from which latter book all reductions to the meridian have also been taken. Itight ascensions, declinations, parallaxes, semi-diameters, and all other elements of the lieavenh bodies which were required in the reductions, have been taken from the American Nautical Almanac. OBSERVATIONS FOE TIME. All observations for time have been made on the sun in the following manner : Suppose the sun to be rising. The index of the sextant was set at an angle a little greater than the. double, altitude of the upper limb ; the angle chosen being always at some whole degree, or else at some 15', 30', or 45', on the graduated are. Then, looking through the telescope of the sextant into the artificial horizon, the two images of the sun were seen separated, but approaching each other, and the instant when the two limbs came into contact was noted. The index was then set forward fifteen minutes, and the same process repeated; after whicJi it was again set forward lift ecu minutes more, and the same process repeated a third time; thus giving three, observed contacts of the upper limbs. The roof of the artificial horizon was next reversed, and the index of the sextant set back to its first reading. Then, looking through the telescope of the sextant into the artificial horizon, the two images were seen overlapping, but separating, and the instant of last contact of the two limbs was noted. The index was then set forward fifteen minutes, and the same process repeated ; after which it was again set forward fifteen minutes more, and the same process repeated a third time; thus giving three observed contacts of the lower limbs respectively at precisely the same altitudes as the corresponding ones of the upper limbs. If the sun was falling, instead of rising, then the same observations were made, but their order was reversed. The advantage gained by observing in this manner is that all correction for semi-diameter is avoided, all errors arising from a prismatic form of the glasses in the roof of the artificial horizon are eliminated, and even for a very accurate reduc- tion there is needed only a single computation of the refraction. The reduction of observations for time has been effected by means of the following formula 1 : a > r + p i. s sin = A/ 8 " 1 (^ rt ) ' cos ^ ' s c <p . cosec d In which T = mean of observed chronometer times. {2 = mean of observed double altitudes. 01 = correction for index error, eccentricity, &c. r = refraction. p = parallax. it = semi-diameter. a = the geocentric altitude of the center of the object observed. d = polar distance of object observed, measured from the elevated pole. y = latitude of place where observation is made. tf = hour angle, at the pole, of the object observed. T== equation of time. <Zt= correction of the chronometer to reduce the reading of its face to local mean time. Appended is a specimen of the form upon which the observations were recorded and reduced. Most of it will be sufficiently intelligible without any explanation. Under the head, "Index cor- rection, &c.," the columns "On arc" and "Off arc" are used when the index correction is deter mined from the sun ; that headed " Coincidence of images" when it is determined by observing a star. 5* 34 REPORT OF PROFESSOR HARKNESS. With some instruments it is possible that the measures of the sun's diameter made on and off the arc may require correction for eccentricity. In such a case the correction is inserted on the line "Eccentricity," and by adding it to \ (<' <) the true index correction is obt-ained. The quanti- ties r h <7, B, F, and 'Art. Hor., are all functions of, and vary with, the measured angle to which the index correction is to be applied. (In this example 84 -t.5f.) r t is the correction for want of paral- lelism between the line of sight of the telescope and the plane of the sextant; a is the correction for a prismatic form of the index glass; E is the correction for eccentricity, a table of which for this instrument is given on page 31 ; F is the correction for a change of index error dependent upon the position in which the sextant is held, or in other words, for flexure; Art. Hor. is the correction for want of parallelism in the surfaces of the glass composing the roof of the horizon ; a table of its values for the horizon Ha. 1 is given on page 32, but when, as in the present case, half the observa- tions have been taken with the roof in one position, and the other half with it reversed, the error eliminates itself and the correction is zero. Observations for SMioii, DCS Moiiies, Iowa Instrument, Sextant - Artfticial Horizon Chronometer Observer, Wm. Harkness - Time. Date, August 1, M<u'l; t >lr <( />Vo., No. 937. Folding Mercurial, Ha. 1 T. & & J. D. Nfym, So. 1319. Object, S'i<n. Double Altitude. Limb observed. jj Chronometer. o in 85 A h. in. *. 9 30 8. 5 84 45 U U 30 .M..-> 84 30 u 11 31 33. 6 85 B 33 5. 84 45 tt " 33 47. 1 Sums. Means. Index Corr., &c. Q 84 30 " u 34 29. 4 . 13 55.1 84 45 0. 4- 2 31. 1 9 32 19.2 Thermometer 74.0 84 47 31. 1 in 42 23 45. 5 Barometer 29. 7(i Retraction. 59. 5 At, Thor. Parallax. -f- 6.3 Semi-diam. 42 22 52. d 73 44 59. 2S S 41 35 :!. 157 43 27 78 51 44 S S6 28 52 o i a -f Hi 15 0.6 Declination of object Polar distance of object 73 44 59.4 OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1309. 35 Ottfeot Index Correction, &c. On are = u Off arc = u' Coincidence of Images. Sums. Means. w' <j i (u' u) Eccentricity Index Corr. ;; anil c E F Art. Hor. Index Corr., &c. t it 20 :so 25 25 O ' " 4 20 5 5 / // 80 10 29 26. 7 33 511. 7 4 20 3. 3 Sin (S a) CosS Sec <j> Cosec d Sin* i H Sin | II Logarithms. + 4 :',<). o 9.774194 9. 285937 .126171 . 017707 + 2 15. 0.0 + 2 15. 0.0 + 10.1 0.0 0.0 9. 204009 9. 602004 / li. m. s. 3 8 36.0 + 5 2f>.2 + 2 31.1 Local Apparent Time 314 2. 2 9 32 19.2 Time liy Clironoinetei Chronometer t'asf nf 1 Longitude west of \Vi Chronometer fast of- \ These oliscrvatk 0. 38 of an inch inn* from index error. ocal Mean Time 6 18 17. 1 6 16. Washington Mean T us were made after t In 1 subtracted t'rni 5 12 1. noon. n tin' rending of the barometer to free it The observations for time are given in detail in Schedule A, appended to this report, but for con vcn fence of reference the following .abstract of them is inserted here. The column headed " Mean" is the menu of the forenoon and the afternoon observations, and is taken to be the error of the chronometer at noon. In cases where (here is only one set of observations in the forenoon, and two sets in the afternoon, in taking- the mean 1 have given the morning observations double weight, because there seems to be a constant difference between them and the afternoon ones. 36 REPORT OF PROFESSOR HARKNESS. Chronometer T. 8. & J. D. Negus No. 1,319, fast of Dot Mo! in* time, by obxercutiou. Date. A.M. P.M. Menu. 1,'nily rate. Hourly rate. /I. Wl. *. 8. /i. in. . -. 8. July 93 6 18 8. 4 7.4 6 18 8.0 23 7.9 - 0. 47 0. 020 24 8.9 26 9.8 8.9 9.4 27 10.6 . . . 1.05 .044 27 10.8 28 12.3 10.7 11.5 . 28 10.9 0.50 .021 29 1-2.4 11.8 12.0 29 11-. 6 . 0.20 .008 30 12.0 12.6 12.2 30 12.5 11.9 . 1.40 .058 31 13.8 13.3 13. 6 31 13.9 13.6 0.45 .019 Aug. 4 15.1 15. 7 15.4 0. 63 0. 026 7 17.2 17.0 17.3 7 17.9 17.0 . + 0.20 +0. 008 8 6 18 16.9 17.2 6 1 17. 1 As the time is of very great importance on the day of the eclipse, I have obtained the chronom- eter error employed on that occasion, as follows : The telegraphic comparison made at Des Moines on the evening of August 7, 1869, between my mean-time chronometer, T. S. and J. 1). Negus No. 1319, and the Kesscls sidereal clock at Washington, gave 31, 4 m 55.30, Negus = 19 h O m O s .O, Kessels. Then we have h. HI. 8. Time by face of Kessels 19 0.00 Kessels fast - - 27.16 Washington sidereal time Sidereal time of mean moon Sidereal interval Acceleration on mean time Washington mean time Time occupied by passage of signal from Washington to Des Moines Des Moines west of Washington Des Moines mean time Time by Negus, 1:519 Negus i:;i!, fast I (ate from noon Negus 1."I9, last at noon - At the time of the eclipse this chronometer was therefore Qb 18"' 17 8 .2fast 18 59 32.84 9 1.50 9 54 31.34 1 37.40 9 52 53.94 + 0.21 16 10.09 8 46 38.06 3 4 55.: !0 6 18 17.24 0.10 6 18 17.14 OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 18C.9. 37 of DCS .Monies mean time. I have thought it best to determine its error in this way because by so doing it is niiiile to depend upon seventeen sets of time observations, instead of upon four sets, as would he tin 1 ease if the observations of August 7 only were used. For an explanation of the rate employed for this chronometer, and the error of tbe Kessels clock, see pages 42 and 43. OIJSKItVATIONS FOK LATITUDE. Circum-meridian altitudes of the. sun for latitude were observed as follows: Three double alti- tudes of one litnli were taken, and then the roof of the artificial horizon was reversed, and three double altitudes of the other limb observed. Thus the semi-diameter of the sun, and all errors depending upon any imperfection of the roof of the artiticial horizon, were eliminated. It is perhaps scarcely necessary to add that the time was noted and recorded at the instaut of observing each double altitude. ( 'ireum -meridian altitudes of stars were observed in the same way as those of tbe sun, except that the coincidence of images was taken instead of the contact of limbs. The reduction of the observations for latitude Las been effected by means of the following formula- : * -JT- ]_ ] ~ 80400 J f 1 T fc = ,)T ;K SliKIO Log. i = 0.00237. When the sun is observed with a mean-time chronometer, , COS if. COS" A :=^ tC - Sill *| When a star is observed with a mean-time chronometer, . . COS y. COS A = KI. sin Ci B A- 1 , col :, 2 sin 2 i t m= . , - sin I" siiiT /7 ~ fi = + >' p is A m + B n <p=^ + o In which fl = niean of observed double altitudes. = correction for index error, eccentricity, &c. r = refraction. jj = parallax. a semi-diameter. <5T==rate of chronometer in twenty-four hours, positive when the chronometer is losing. (5E=the increase of the equation of time in twenty -fom boors ; the equation of time being regarded as positive \\hen it is to be added to apparent time. * = hour angle of the object observed. 38 KEPOET OF PROFESSOR IIARKNESS. <J = declination of the object observed; north declinations being' taken positive. For a culmina- tion below the pole, it must be measured from the equator through the zenith to the object : that is, it is equal to 180 S. C = observed zenith distance of object, which is to be taken as positive when the object is south of the zenith. , = true geocentric zenith distance of the object at the time of its culmination. y = latitude of the place of observation. Appended is a specimen of the form upon which the observations were recorded and reduced. That part of it relating to the index correction is precisely the same as in the case of the time observations, and the remainder of it will be sufficiently intelligible, without any explanation. Observations for Latitude. Station, DCS Moines, Iowa Date, July I'l, 1869. Instrument, Sextant - Mackjmlc it Jiro., Xo. 937. Artificial Horizon Foldiiu/ Mercurial, Ha. 1. Chronometer T. fl. & J. D. XMJUK No. 1319. Observer, Wm. Hardness - Object, Sun. Chronometer. Double Altitude. * t. in. a. /). m. X. 6 7-51.5 C J " 136 17 45 111. X. 16 29. 4 533.6 0.7 8 32.0 20 10 15 4H. 11 I'.in. ii .6 9 9.5 22 20 IT, 11.4 45-,>. 9 . 5 JO 11.3 135 23 10 14 9. 6 393. 6 . 4 1(1 55.3 25 10 13 ;.';-,.(; :;.-,:',. 9 . 3 12 7. 29 30 l-> 1 ::.'.> 29::. 7 .2 58 .IH.Ci 18 5 Sums. 251Ki; 2.7 (i "9 47.8 i:;r> r>3 0.8 + 2 50. 5 Mriins. 119..- 0.45 Index Corr., &e. Q to 90 Q = ? Thermometer, 86.0 Barometer. At, Ther. 135 55 51.3 67 57 55. 6 22 2 4.4 Kefraction + 21.7 Parallax 3.2 Semi-diameter . AI - 13 14.5 B fi + 4.0 21 49. 12. <! + 19 46 24. /I. Ml. K. = 12 6 12.0 6 18 8.9 = (;>.) -jo. 9 41 35 36. Time of culmination Chronometer lime 01 OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. Index Correction, &c. Oli.jrrl. Oil air (J Otf arc = w' Ciiinciilciico of Image's. / // 2l "> O ' " i ><; ii / // in 20 in sum*. 2."-. Means. '."I 8.3 33 r>0.0 u' u + 4 -11.7 in 30. 4 i I". l . Sin M Ar. Conij). Logarithms. 9. 5703 H "'-<>) 4- 2 20.8 0.4297 l.c i rntricity. 0.0 Cos <p 9. H?3- Index ( 'HIT. -f 1 20. f ( 'i.- c n.;i7:{(i ^ anil T 0. fc K + 29.7 F 0. i A 0. 2771 Art. lli.r. 0.0 >"o A/ 2. 62:> 2. SMI01 Imlrx Corr., &c. + a r,0. r> A- 0.6542 Ciil fi 0. :!!I74 H 3 B/^ '.1. <i. r >32 0.6048 Ii. in. . II 12.0 1 (5 16. AsMiinnl l,oiif{itii(lf west of Washington BKMAK KS. Observations tor latitude iimde on Polaris when at a considerable distance from the meridian have been reduced by means of the formula <P = Ji p. cos t + i p 2 . sin 1". sin 2 1. tan In which i2 = mean of observed double altitudes. i = correction for index error, eccentricity, &c. r = refraction. jj=polar distance of the star, expressed in seconds of arc. t=.= honr angle of the star. 40 REPORT OF PROFESSOR HARKNE8S. The observations for latitude are given in detail in Schedule. ]>, appended to this report, but for convenience of reference the following abstract of them is inserted here: Observations for Latitude of Temporary Ohxerratory. Date. Object. I.;M it Ililr. 1869. ' II July 23 Sllll 41 :ir. .':, 23 Sun 84 24 Sun 36 25 Sun ....... 29 26 Sun 411 27 Sim 29 28 Sun 42 28 Sun 35 29 Sun 35 29 Sun 33 29 37 29 :) 30 Sun :;<; 30 Sun 34 30 Polaris 40 31 Sun II 31 Sim :!'.) Ann 2 Sun 41 2 Sim 41 2 a Onliiuchi .... 33 2 Polaris 26 2 a Aqnilip 1 4 <i Sngittarii .... 48 Rejecting the observation of a Aquihe made on August 2, the mean of all the observations of the sun and south stars gives for the latitude 41 35' 35".7 i 0".94 And the mean of the observations of Polaris gives 410 35/ 37.o 1 3".95 As these two results differ from each other by a quantity less than their probable error, they afford no evidence that they are affected by any constant errors. 1 have therefore taken as the iinal result of the observations their general mean, which is 41 35' 3f>".9 i 0".t>3 TELEGRAPHIC DETERMINATION OF LONGITUDE. The plan adopted for- the determination of the difference of longitude was to allow the observers at Washington and Des Moines to determine their respective local times in whatever manner was most convenient, and then to compare these times by means of the electric telegraph. For that purpose it was necessary to have the use of the wires of the Western Union Telegraph Company, and our thanks are due to William Orton, esq., the president of that company, for his liberality in granting them to us free of all expense. We are also under obligations to the following named gen tleinen: to Mr. Charles A. Tinker, manager of the Western Union lines in Washington, and to the gentlemen having charge of the wires in Chicago, whose names I am ignorant of, for making the general arrangements necessary to give a continuous line of wire from Washington to Des Moines. OBSERVATIONS OF THK ECLIPSE OF AUGUST 7, 1869. 41 To Mr. M. Marcan, chief operator in tin- Washington office, for coming up to the observatory every evening and assisting' in the management of the, wires during the exchange of signals. To Mr. Monroe A. Smith, manager of the telegraph otlice at Des MoinevS, for assistance and facilities ren- dered to me there ; and to the various gentlemen, whose names I do not know, who had charge of the repeaters at Philadelphia, Pittsburg, C'restline, Chicago, Keokuk, and Davenport, during the exchange of signals. The signals employed in determining the difference of longitude were made by breaking a gal- vanic circuit ; a method which 1 prefer because- the magnets used in telegraphing are much more certain to open promptly when the circuit is broken than they are to close promptly when it is re-established. This is true of a circuit including only a single magnet, but it applies with far greater force when, as in the present case, the distance is so very great that it is necessary to divide it into a number of shorter circuits and to use repeaters to transmit the signals from one circuit to the other. The apparatus employed at the observatory in Washington, both for sending and receiving signals, is entirely automatic, and is fully described in my report on the determina- tion of the longitude of the city of Havana, Cuba. That used at Des Moines consisted of a break circuit key, which I carried with me, and the usual receiving magnet and sounder; the armature of I lie magnet of the sounder being so adjusted as to make its back stroke much louder than its for- ward one. At Washington, the pendulum of the Kessels sidereal clock broke the circuit for somewhat less than one-tenth of a second every time it passed the central point of its arc; thus making a break once every second. Halfway between the clock break corresponding to seconds and that corre- sponding to 1 second, an extra break was interpolated by means of a key worked by hand; thus marking the beginning of each minute by a double break. These signals, after passing through the various intermediate repeaters, finally arrived at lies Moines and were made audible by the sounder there. Sitting beside it, and keeping my eye upon the mean-time chronometer, I waited until the back stroke of the armature of the sounder coincided with the beat of the chronometer. When that occurred I noted the time; and also the time of the arrival of the next following double beat of the Washington clock. Five such coincidences were observed on each night when signals were exchanged, and at their conclusion the Washington operator told me the hour and minute corresponding to the last double beat of his clock. The following record of signals received at Des Moines. from Washington, on the evening of August 7, 1809, is given as a specimen of such work : Cdiiicidc-nc;' of brcak.s with Nuxt following limits of chronometer. double break. It. in. . . 2 30 18.0 01. 33 10.5 00..-, 30 18.0 00.0 39 10.5 59.5 42 18.0 59.0 = IS" 38'" O s .O, Washington clock. Now, as the double breaks correspond to the seconds of the Washington clock, if we add 00 to the observed seconds of the time of coincidence of beats, and then subtract from the sum the sec onds of the time of the next following double beat, the remainder will be the seconds indicated by the face of the Washington clock at the time of the coincidence of beats. Thus, for the first coin- cidence recorded above, (JO" + 18 s .O 01 s .O = 17 s .O. The last recorded coincidence and double beat give, not only the seconds of the Washington clock, but the hour and minute also; thus furnishing the means of supplying the hour and minute to each of the other coincidences. Proceeding in that manner with the record given above, we obtain Chronometer. Washington clock. h. m. . It. in. s. 2 30 18.0 18 25 17.0 33 10.5 28 10.0 30 18.0 31 18.0 39 10.5 34 17.0 42 18.0 37 ' 19.0 6* 42 REPORT OF PROFESSOR HARKNESS. These are the desired comparisons of the clock and chronometer, obtained at DCS Moines. In order to eliminate the time occupied in the transmission of the signals, it was necessary that a .sim- ilar set of comparisons should be obtained at Washington. For that purpose, as soon as the com- parisons at Des Moines were finished, the otliccr at Washington put his clock out of the main cir- cuit, and arranged his chronograph so that while it recorded the beats of his clock it would also record along with them the signals sent from DCS Moines. Then, placing my hand above, but not in contact with, the break-circuit key, 1 beat seconds with my linger, in coincidence with the beats of my chronometer, touching the key at every beat, but only pressing it hard enough to break tin- circuit at the beats corresponding to 0, 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 0, &c., &<., seconds. Thus breaks were transmitted to Washington, and recorded upon the chronograph, at regular inter- vals of five seconds, and the beginning of each minute was marked by a double break. Finally, after a sufficient number of such signals had been sent, 1 telegraphed to Washington the hour and minute indicated by my chronometer at the last double break. The following record of the breaks received at Washington from Des Moines, read from the chronograph sheets of the evening of August 7. 1809, is inserted as a specimen of such work. Each comparison consists of nine signals; namely, all those occurring at intervals of live sec- onds between 40 seconds of one minute and 20 seconds of the next following minute, by the face of the chronometer. As the chronograph has but a single pen, by which both the clock beats and the signals are recorded, in order to avoid inaccuracy in reading off the sheets, no use is made of sig- nals which occur very iiear the time of coincidence of beats of the clock and chronometer. Chronometer. h. m. a. 2 49 0.0 Washington clock. Chronometer. *.40 .40 .50 A. m. .45 A. TO. 9. 18 44 2.43 2 50 0.0 .40 .50 .55 .50 \V:isliingioii clock. Chronometer. Washington clock. a. 8. .55 .70 ' .60 .SO .(iO .85 li. m. .60 //. m. 8. A. m. .80 18 45 2.05 2 51 0.0 18 46 2.SO .70 .88 .85 .80 .70 .88 .70 .90 Taking the means we get Chronometer. li. m. s. 2 49 0.0 50 0.0 51 0.0 Washington clock. /I. Ml. K. 18 44 2.46 45 2.66 46 2.82 which are the desired comparisons of the clock and chronometer, obtained at Washington. As our temporary observatory at Des Moines was more than three-quarters of a mile from the telegraph office, in order to guard against the introduction of any error into the longitude, by the chronometer tripping while it was being carried from one place to the other, 1 always compared it with the mean-time chronometer T. S. <S: J. I). Negus No. 1300, immediately before starting for the telegraph office, and again immediately after returning from it. 1 always walked from one place to the other, and carried the chronometer in my hand, so as to subject it to as little motion as pos sible. The observations for time at Washington are given in full in Schedule (', appended to this report. They were made with the east transit instrument, by Professor M. Yarnall, U. S. N., who has also reduced them and furnished me with the clock errors which I have employed. The error of the chronometer Negus 1319, on Des Moines mean time, during the exchange of longitude signals on the evenings of July 26, 29, 30, and 31, has been obtained from the hourly rate and error at noon given for that chronometer on these days respectively in the table on page 36. For the evening of August 7 the error has beeu found as follows: From July 23 to August 7 the time observations show that the chronometer was steadily gaining ; while the observations of August 8 show that OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 43 during the twenty -four hours preceding tin- noon of tlmt day it lost two-tenths of a second. The question arises whether the change of rate took place before or after the exchange of longitude signals on August 7. To answer that question we have the following comparisons of chronometers : \rj;iis lliOO. Negus 1H19. 1869. ft. in. s. ft. in. 8 August 7 : 6 0.0 = :! 8 8 6 7 12 57 0.0 = 12 59 8 7 7 16 8 0.0 = 16 10 8.7 8 6 38 II. = 6 40 8 1 As the longitude signals were exchanged between 14 h 30 m and lu h O m , by the face of Negus 1319, these comparisons seem to indicate that the change of rate took place afterwards. The observations make Negus 1319 C 1 ' 18m 17 S .3 fast at noon of August 7, and for the preceding ten days it gained on aw average 0.58 of a second per day. Hence, its error at the time the signals were exchanged would be 6 h 18 m 17 S .50. I have pre- ferred to use a slightly less value, and have, adopted G 1 ' 18'" 17".4 fast. Throughout the following record of the exchange of signals, the error of the Kessels clock is given on Washington sidereal time, and the error of the chronometer Negus 1319 on mean time at our temporary observatory in Des Moincs. On account of the great distance between the two cities, it was impossible to transmit tele- graphic signals directly from Washington to DCS Moines; therefore the line was broken up into a number of circuits of moderate length, and the signals transmitted from one circuit to the other by means of automatic repeaters; the arrangement of which depended upon the electrical condition of the wires, and the exigencies of the business of the telegraph company, and was varied from night to night; the particular arrangement made use of on each night being stated in the record of that night's work. The number of statute miles of wire, exclusive of the wire in the magnets, the kind of repeaters, and the amount of battery used on each circuit that was employed, were as follows: Washington to Philadelphia, 138 miles. Thirty drove cups at, Washington. A Hix repeater and thirty drove cups at Philadelphia. I'hilailelphia to rittstburg, 355 miles. A Hix repeater and fifty Grove cups at Philadelphia. A Hix repeater and sixty-five drove cups at Pittsburg. Fittxlmrg 1<> Crcxtliiic, 189 miles. A Hix repeater and sixty-five Grove cups at Pittsburg. A Hix repeater and seventy-five Grove cups at Crestline. Crestline to Chicago, 270 miles. A Hix repeater and seventy-five Grove cups at Crestline. A Hix repeater and sixty Grove cups at Chicago. Pittsburg to Chicago, 408 miles. A Hix repeater and sixty-five Grove cups at Pittsburg. A Hix repeater and sixty Grove cups at Chicago. Chicago to KcoJmk, 251 miles. A Hix repeater and sixty Grove cups at Chicago. A button repeater and two hundred and fifty cups of Hill's battery at Keokuk. Keoltulc to Des Moines, 101 miles. A button repeater and two hundred and fifty cups of Hill's battery at Keokuk. Ninety cups of Hill's battery at Des Moines. Chicago to Davenport, 183 miles. A Hix repeater and sixty Grove cups at Chicago. A button repeater and sixty-five Grove cups at Davenport. Davenport to Des Moines, 174 miles. A button repeater and sixty-five Grove cups aj Daven- port. Ninety cups of Hill's battery at Des Moines. Hill's battery is a modification of Darnell's, each cup consisting of a glass jar, about seven 44 REPORT OF PROFESSOR HARKNESS. inches high and six inches in diameter, with a sheet of copper placed in the bottom, and a disk of zinc, perforated in the center, suspended horizontally about five and a half inches above the copper. Each of these plates has a surface of about twenty-eight square inches, and has attached to it a gutta-percha covered copper wire, which forms one pole, of the battery. The jar is tilled with a solu- tion of sulphate of zinc, after which a few crystals of sulphate of copper are dropped in through the orifice in the /inc, and lie on the copper plate. If the liquid is not agitated the copper plate will lie in a solution of sulphate of copper, and the zinc plate in a solution of sulphate of zinc, so long as the specific gravity of the latter is less than 36 li. The porous cell, used in Daniell's battery, is therefore dispensed with. For telegraphic purposes seventy cups of Hill's battery are considered equal to forty-three cups of Grove. The difference between a Hix and button repeater is, that, when a llix repeater is properly adjusted, signals can be sent through it with equal facility in either direction ; while if signals are being sent through a button repeater in one direction, before they can be sent in the opposite direc- tion an attendant must change the connections of the wires. This is done by means of a switch, or button ; hence the name, " button repeater." In the case of all repeaters, signals going in one direc- tion pass through a different set of magnets from those going in the opposite direction; therefore there never can be any security that in any given case the signals going in opposite directions occu- pied the same, length of time in their transit; however, as the repeaters will only work within very narrow limits of adjustment, aiwl as the, combined wave and armature time varies so little on different nights, the error originating from this source must be exceedingly small, and in the mean of five nights it is probably entirely eliminated. The total length of wire, exclusive of that on the magnets, between Washington and Des Moines, via Keokuk, is 1,373 miles ; and via Davenport, 1,318 miles. KKCOKD OF EXCHANGE OF SIGNALS. July 21 i, 1800. Uepeaters at Philadelphia, Pittsburg, Crestline, Chicago, and Keokuk. Comparison of chronometers to show whether or not Negns 1319 suffered any appreciable change in its error while being carried to the telegraph office and back : Negn 1300. Negus 131!'. li. m. s. /i. m. x. 11 22 0.0 11 24 7.8 5 47 0.0 5 49 8.0 Kessels clock, 22 s . 45 fast. Chronometer Negus 1310, G 1 ' 18"' 9 S .S fast. Comparisons of clock and chronometer by means of signals received at Des Moines: Negus 1319. Kessels. /I. III. #. ll. III. H. 3 57 55.5 19 5 53.0 4 50.0 8 48.0 52 50.5 20 57.0 55 41.0 3 48.0 4 58 50.5 G 58.0 5 1 52.0 10 0.0 Reducing all these comparisons to the same instant, we get Negns 1319. Kessels. ft. m. K. li. m. *. 3 52 3.47 10 0.0 3.44 3.49 3.45 3.47 3.47 OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 45 Taking the mean, applying the clock and chronometer errors, and reducing the Washington sidereal time to tlic corresponding mean time, there results Wasliiii-itnn. Des Moiiics. Dift'. longitude. .10" 40'" ! s .r,.-) 9" .33 5.T.60 1" 6'" 15 S .89 Comparisons of clock and chronometer by means of signals received at Washington: NCfJUS liil'.l. Krssrls. /I. III. . /I. III. 0. 4 10 0.0 lit 17 59.87 12 0.0 liO 0.21 i:i 0.0 21 0.38 Reducing all these comparisons to the same instant, we get Nl'gll.s KU',1. Krssrls. 7i. in. . /i. 111. i. 4 10 o.o 10 17 r>9.87 39.88 59.89 Taking the mean, applying the clock and chronometer errors, and reducing the Washington sidereal time to the corresponding, mean time, there results \V:ishini;toii. Des Moines. "Dill', longitiulp. 10" 58" Cr.lS 9" 51' 50.20 I' 1 6'" 1G".2S The difference of longitude found from the signals received at Washington necessarily varies from that found from the signals received at 1 )es Moines. The mean of the two results is l h 0'" l(i s .OS, which is the true dilferenee of longitude given by this evening's work. Half the difference between the two results is 0.20 of a second, which is the time occupied in the passage of a signal from one city to the other. As repeaters were included in the circuit, this is the combined effect of wave and armature time, and gives no clue to the speed of the galvanic, current. </nltl 29, 1809. Itepeatcrs at Philadelphia, 1'ittsbnrg, Chicago, and Keoknk. Comparison of chronometers : Negus 1300. Negns 1319. /i. m. . li. m. 10 14 0.0 10 1C 8.2 4 14 0.0 4 16 8.4 Kessels clock, 20V>:: fast. Chronometer Negus 1319, 6 h 18 12 s .l fast. Comparisons of clock and chronometer by means of signals received at Des Moines: Negus 1319. K.-ssels. ft. m. s. It. m. 8. 2 45 10.0 18 4 41.0 48 5.5 7 37.0 51 15.0 10 47.0 54 14.5 13 47.0 57 13.0 10 46.0 Reducing all these comparisons to the same instant, we get Negns 1319. Kesscls. /I. 111. *. A. 71). S. 2 40 29.77 18 0.0 29.75 29.76 29.74 29.75 46 REPORT OF PROFESSOR IIARKNESS. Taking the mean, applying the clock and chronometer errors, and reducing the Washington sidereal time to the corresponding mean time, there results Washington. Des Moincs. J>ilV. longitude. ii' 1 2s' 33 s .75 s 1 - 22-" i7 s .or> i 1 ' 6- i5 s .< Comparisons of clock and chronometer by means of signals received a) Washington: Negus 1319. h. m. s. Ii. m. s. 3 17 0.0 18 36 36.60 18 0.0 :;7 36.74 19 0.0 38 36.89 Reducing all these comparisons to the same instant, we get Negus 1319. Kessds. 7i. MI. s. h. m. n. 3 17 0.0 18 36 36.60 36.58 36.56 Taking the mean, applying the clock and chronometer errors, and reducing the Washington sidereal time to the corresponding mean time, there results Washington. Des Moines. Diff. longitude. 10 1 ' 5'" 4 s . 15 8" 58 47.90 1" (i 1 " .16 S .25. This evening's work, therefore, gives /I. III. 8. Difference of longitude 1 t! lii.O'.l Wave and armature time 0.16 July 30, 1869. Repeaters at Philadelphia, Pittsburg, Crestline, Chicago, and Keokuk. Comparison of chronometers : Xegus K!00. Negus 131 !. /I. III. t>. ll. III. K. 11 21 0.0 11 23 s.s 5 36 0.0 5 38 9.0 Kessels clock, 21".20 fast at the time of the Des Moines comparison ; L'l',17 fast at the time of the Washington comparison. Chronometer Negus 1319, C 1 ' 18 m 12 B .7 fast at the time of the, Des Moincs comparison ; 6 1 ' IS> 12 S .8 fast at the time of the Washington coni])arison. Comparisons of clock and chronometer by means of signals received at Des Moines: Negus 1319. Kessels. 7i. m. s. Ii. HI. *. 3 47 3.5 19 10 41.0 50 5.0 13 43.0 53 7.5 16 46.0 56 5.0 19 44.0 59 6.5 22 46.0 Reducing all these comparisons to the same instant, we get Negus 1319. Kessels. h. m. *. Ji. m. s. 3 36 24.25 19 0.0 24.25 24.25 24.23 24.23 OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 47 Taking the iiu'iin, applying the cluck and chronometer errors, and reducing the Washington sidereal time to the corresponding mean time, there, results \Yiiliin<rloii. Jlcs Muincs. Dili'. linifjil mlr. Ill 1 ' 21'" 27MO <J h 18'" 11 ".51 I 1 ' <>'" 15.G2. Comparisons of clock and chronometer h.y means of signals received at Washington: Nri;iis I'.ili). Keswels. It. m. s. A. nt, ,s. 5 3 0.0 20 'M 50.20 4 0.0 27 50.42 5 0.0 28 50.57 Reducing all thesv comparisons to the same instant. \ve get Nf<;iis KS19. Krssrls. /'. lit. .v. /*. in. x. 5 ;{ o.o i'o liii ."lO.^'ii .-.0.2G 50.24 Taking the mean, applying the clock and chronometer errors, and reducing the Washington sidereal time to the corresponding mean time, there results \Viisliin<r|<>ii. DCS MoineH. Hill', longitude. 11" 51'" 3.21 10" 44'" 47 K .2() 1" 0"' Ki'-.Ol. This evening's work, therefore, gives h. ' m. s. Difference of longitude 1 <i 15.82 Wave and armature time ' ()' 0.20 .lull/ :>1, lS(i!. Kcpcaters at I'liiladelphia, I'ittsburg, Crestline, Chicago, and Keokuk. Comparison of chronometers: N.-MIIS 1300. //. in. s. 1 1 3 0.0 5 9 0.0 Negus i:;i'.i. A. m. x. 11 5 8.9 5 11 9.0 Kesscls clock, L'1\S:; f;ist. ChroiKuneter Negus l.'5H, (i h IS"' liKS fast. Comparisons of clock and chronometer by means of signals received at Des Moines: Negus 1319. Kessds. /I. !. . It. m. 8. 4 2 17.5 19 29 51.0 5 15.0 32 52.0 8 17.5 35 5.5.0 23 20.0 51 0.0 20 17.5 53 58.0 Reducing nil ihesc comparisons to the same instant, we get Kcssels. A. IH. n. li. m. 8. '< 32 28.40 1!) 0.0 28.38 28.38 28.36 28.34 Taking the mean, applying the clock and chronometer errors, and reducing the Washington sidereal time to the corresponding mean time, there results \V;iKliin s -|iiii. DCS M, lines. I (ill', longitude. 10" 20"' 30.<;:; 9" 14'" 14 8 .57 I 1 ' lu 9 .OG. 48 REPORT OF PROFESSOR HARKNESS. Comparisons of clock and chronometer by means of signals received al Washington : Negus 1319. Kessrls. /i. m. s. li. m. x. 4 20 0.0 19 57 41. -44 31 0.0 58 41.58 32 0.0 5!) 41.74 Reducing all these comparisons to the same instant, we gel Negus 1319. Kessels. /I. m. s, H. tn. x. 4 30 0.0 1!) 57 41.44 41.42 41.41 Taking the mean, applying the clock and chronometer errors, and reducing the Washington sidereal time to the corresponding mean time, there residts Wellington. Dew Moines. I (ill. longitude. 11" 18 m 2".0 10' 1 Jl> 40 8 .20 I 1 ' 0'" JIJ-.40. This evening's work, therefore, gives /I. III. X. Difference of longitude 1 <; i<>.23 Wave and armature time n 0.17 August 7, 180!). Repeaters at Philadelphia, Pittslmrg, Chicago, and Davenport. Comparison of chronometers : Negus 1300. NYgiis 1319. h. m. x. h. in. H. 12 57 0.0 12 59 8.7 4 8 0.0 4 10 8.7 Kessels clock, 27M(5 fast. (Chronometer Negns 1319, 6 h 18'" 17".4 fast. Comparisons of clock and chronometer by means of signals received at Des Moines : Negus 1319. Kcsscls. /i. m. . /i. m. . 2 30 l.S.O 18 25 17.0 33 10.5 28 10.0 3G 18.0 31 18.0 39 16.5 34 17.0 42 18.0 37 19.0 Reducing all these comparisons to the same instant, we gel N.-gUS 1319. hYssrls. /I. HI. S. /I. HI. H. 3 4 55.31 19 o.O 55.30 55.30 55.30 55.28 Taking the mean, applying the clock and chronometer errors, and reducing the Washington sidereal time to the corresponding mean time, there results Washington. Des Moines. Mitt', longitude. 9 h 52"' 53 8 .94 8 h 40 m 37 8 .90 I 1 ' li'" 1<;.04. Comparisons of clock and chronometer by means of signals received at Washington : OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 18fi9. 49 Negus 1319. It. iw. s. 2. 49 0.0 r.o o.o 51 0.0 Kessels. li. m. . 18 44 2.46 45 2.66 46 2.82 I {oil iiciiig- all these comparisons to the same instant, we get Negus 1319. Kessels. /I. 711. *. /I. 'III. S. 2 49 0.0 IS 44 2.46 2.50 2.49 Taking the mean, applying' the clock and chronometer errors, and reducing' the Washington sidereal lime to the corresponding mean time, there results \V:ishinn'l<>ii. lies Moines. Dill', longitude. 9 h 36'" 59 8 .04 S 1 ' :!0' 42".GO 1" 6 1 " 16 9 .44. This evening's work, therefore, gives li. m. Difference of longitude - Wave and armature time KexuU from the exchange of signals. Collecting the results obtained from the different nights' work, \ve have ti 16.24 0.20 \Vavc :in<l Date. Diff. longitude. armature time. 1869, It. III. K. X. July 26 1 (i If,. 08 0.20 89 1C. 09 . ii; :to 15.82 .'JO 31 10.23 .17 Aug. 7 16. 24 0.20 Taking tlie mean, we find that our temporary observatory at Des Moines was I 1 ' 6"' 16 S .09 Qs.OS west ot the east transit instrument of the United States Naval Observatory at Washington. But the east transit instrument is 42.9 feet, which in this latitude is equal to 0.036 of a second of time, to the east of the center of the dome. Hence we, have as the result of these signals that the tempo- rary observatory at Des Moincs was I 1 ' G 1 " 16 S .05 0- s .05 west of the center of the dome of the United States Naval Observatory at Washington. From a series of observations made since my return to Washington, I have satisfied myself that if any personal equation exists between Professor Yarnall's determination of the time with the east transit instru- ment and my determination with the sextant, it is so small as to be entirely hidden by the acci- dental errors inseparable from sextant observations. TEIANGULATION CONNECTING THE VARIOUS TEMPORARY OBSERVATORIES. In order to ascertain the relative positions of the temporary observatories of the different astronomers who might be at Des Moines, 1 took with me several small pocket surveying instru- ments, which were the best at my command. Subsequently Colonel J. W. Otley, engineer of the Des Moines Valley railroad, kindly lent me a small theodolite, which was much better adapted to the accomplishment of my purpose, and with which, in connection with Dr. C. H. F. Peters, I exe- cuted the triangulatipn shown in Plate III. The theodolite was made by Spears & Co., of Dublin, and was of the English pattern, the range of the telescope being limited to altitudes not much greater than sixfy degrees. Its horizontal and vertical limbs were each five inches in diameter, 50 EEPOET OF PROFESSOR IIARKNESS. divided to thirty minutes, and read, the horizontal limb by two verniers, the vertical limb by one vernier, to single minutes. The telescope had a focal length of nine and one-quarter inches, a clear aperture of one inch, and a magnifying power of thirty diameters. The base-line was situated upon a low level island in the DCS Moines Uiver, to the east of our observatory, and, from two very careful measurements made with the Chesterman metallic tape, was found to be l,0.'>l ) ..')fcet=314.72 meters* in length. The signals North IJase, South P.ase, Kast Signal, and West Signal, were Hags attached to small poles eight or ten feet high. The signal "Naval Observatory " was the south peak of the roof of our temporary observatory. The signal " Litchfield Observatory" was a Hag placed on the east side of the temporary observatory occupied by Dr. ('. H. P. Peters and party. The signal "Court-house" was the center of the dome of the ( 'onrt house. Near it Professor Simon Newcomb, United States Navy, and Professor ,1. K. llilgard, United Stales Coast Survey, with their parties, observed. In almost all cases the angles between the different signals were measured both by Dr. Peters and myself, each of us repeating the angle six times. The results are given in the following table the column headed "II" containing my measures, that headed "P" Dr. Peters's measures, and that headed "concluded" the concluded value of the angle, which is generally the mean of the results contained in the columns " II" and " P." In the case of the angles at West Signal I have rejected Dr. Peters's measures because they were made a day later than mine, and I am almost certain that during the interval some of the signals were disturbed by cattle: Alixlwt of (Hwrrnl AiKjlrx. Date. Station. Object. X umber of repetitions. Observed angle. H. P. Concluded. 1869. Aug. 3 East Signal Court-house and,Sonth Base . 6 i n 65 27 CO.tl 53. :\ 56.6 Coort-boiiBe and West Signal . . . 68 32 36. 2 30.5 33. 4 South Base and North Base .... r> 40 38 22. 5 34.2 28.4 West Signal and Naval Observatory r, 2 20 0. 41.7 20.8 Litchfield Observatory and Court-house r. 67 49 2.5 2.5 2.5 Litchn'eld < Misei valory Court-house and Weat Signal (i 69 44 25. 19.2 22. It Xnrtli I'.ase Court-house and Litchlield Oliservatory Kast Si (r n;tl ;i]id South Base 1 6 <; 2 28 55 10 17.5 :;t yti 55.0 36.6 63.3 96. a 59. > South Base and West Signal .... South Base and Naval Observatory . - 6 II :,-> 19.2 10.8 15.11 South Base North Base and Kast Signal .... (i 84 11 I'.l.? 1.7 11). 7 West Signal and North Base .... r> 86 4 f,(l. II 5-.'. 5 56.2 Kast Signal and Court-house .... 6 97 33 42. 5 56. 49.2 West Signal and Naval Observatory 6 3 22 40. 43. 3 41.6 Wrst signal North Base and South Base .... (i <;-> 34 50.6 511.0 4 North Base and South liasc .... 6 62 34 20.8 3 North Base and East Signal - - -. - r> 55 56 34.2 34.2 4 Xorth Bane and East Signal .... 6 55 56 11.7 3 Kast Signal and Court-house .... 86 2 57.5 51. 2 4 Kast Signal and Court-house .... 6 86 2 45. 108.3 Litchlield Observatory and Court-house C> 74 47 43.3 %. 7 I: 1 ,. :: Court-house and Naval Observatory 1 110 20 Naval Ohscr\atory and North I'.ase . . 1 107 35 * I have taken 1 meter at 32" Kahr. ==3<.3(>f5 inehes at 62" Fahr. tThe theodolite could not be placed in the position occupied by the signal " Lilclilicld Observatory," and therefore it was jilaeed eccentrically at a distance of 5s. (Mi l'eet= 17.70 meters. The reduction to the center, computed ill the usual manner, is 1 17' 4".2, to be added to the angle given in the table. Hence. Hie tr bserved value of the angle between Court-house and West Signal is 7.1" 1' 26".3. OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 51 Converting these observed angles into observed directions, we yet the numbers given in the third column of the following table : Table of Observed and Adjusted Directions. Station. Object. Observed direction. Correc'n by adjustment. Adjusted direction. o ' // // ' II East Signal .... Litehlield Observatory . . o o o.n - 7.5 359 59 52. 5 Court-house 67 49 2.5 3.2 67 48 59. 3 Smith Base 133 16 59.1 - 2.6 133 16 56. 5 \\Ysl Signal . , 136 21 :i5.9 + 21.6 136 21 57. 5 Naval Observatory . 138 41 56. 7 + 13.2 138 42 9. 9 North Base I"! 55 27.5 - 15.8 173 55 11.7 Litehtield Observatory Court-house (I 0.0 - 22.6 359 59 37. 4 West Signal 71 1 36.3 + 22.6 71 1 48.9 North Base .... Kasl Signal South Base 0. 55 10 26.2 + 14.0 + 8.0 14.0 55 10 34.2 West Signal 86 31 25. 4 - 22.0 86 31 3. 4 South BMM- .... Naval Observatory . \orlh Base 100 a 41.2 0. - 2.5 5.6 100 2 38.7 :!59 59 54. 4 East Signal *4 11 16.7 + 2.3 84 11 19.0 Court-house 181 45 5.9 + 8. 5 HI 45 14.4 \\Yst Signal 27:! 55 3.8 - 5.2 273 54 5S.ll \VeM Signal . \a\al Observatory - . . Nortli Base 277 17 15. 1 0.0 + 1-4 + 19.6 277 17 46.8 19. 6 Kasl Signal 55 5i :;!.> - 18.2 55 56 16. Soulli Base 62 34 50. + 4.6 62 34 54. 6 Lituhlield Observatory . . 07 11 42.1 + 1.9 67 11 44.0 Court-house 111 51) 25.4 5.8 141 59 19.6 Naval Observatory . . . 252 25 25. 2.0 252 25 23. 1 n order to facilitate the adjustment of this triangulation by the, method of least squares, I have adopted the following notation : 1= North Base. 2 = South Base. 3 = East Signal. 5 = Naval Observatory. (>== < Conrt-house. 7 = Litchfield Observatory. 4 = West Signal. 1 2 :> would, therefore, denote the angle North Base, South Base, East Signal ; () woidd denote the direction from South Base to North Base; and (:|) would denote the direction from South Base to East Signal. Hence ( 2 + 2) would denote the angle 123. Proceeding in the usual manner,* the quadrilateral 1324 furnishes the side equation sin 142. .sin 123. sin 134=sin 124. sin 132. sin 143. and the three angle equations 1800 = 132 + 321 + 213 1800 = 124 + 241 + 412 1800 = 134 + 341 + 413 from which we, derive the equations of condition 0= + 29.6 + 0.4(1) + ;,.! (j)_(U(i) + 0.2 (>) 2.8(J) + 0.3 () + 0.2 (4) + 2..1 (jj) - 1.5 (<) I. 0=+ 11.3- (j) + (J)_(i) + (|) -(?) + (?) II. 0= + 111.2 () + (J)-(J) + (>)_() + () jv. 1 See a paper by Charles A. Schott, csq., in the United States Coast Survey Report for 1854, page 80* vt xcq. 52 REPORT OF PROFESSOR HARKNESS. The quadrilateral 2346 furnishes the side equation sin 632. sin 462. sin 342 = sin 263. sin 246. sin 234. from which we derive the equation of condition 0= +137.7 7.9(g) + 47.1(i) + 32.8(5) 14.7() + 21.2(!>) 14.:{(j) 18.1(5) 6.0(:!) 3!).-'(J) V. These five equations of condition give rise to the following Equations of correlatirfx. V oiKi o-iKj o 3 K 3 0& 5 K 5 (?) + 1 -I (?) - 1 1 (1) + 1 + 1 (1) 0.4 - 1 + 1 (I) + 0.2 + 1 6.9 ) + 0.2 - 1 14.3 (i) + 21.2 cj) + o.:i + 1 + 1 CD + 2.5 - 1 + 47. 1 (i) 2.8 - 1 39.2 (i) - 7.9 (3) + 11.4 - 1 - 1 (!) + 1.1 + 1 + :.8 (I) 1.5 + 1 - 18.1 (5) - 11.7 K 4 = 20.2 K 5 = + 0.31)9 The resulting normal equations are 0=+ '29.6+ 18.04 K, + 11.3- 1.60 + 6.00 K 2 + 45.4+ 0.10 - 2.00 + 6.00 K 3 + 111.2 + 1.20 + 2.00 + 2.00 + 6.00 K 4 + 137.7 + 286.50 -54.00 +47.10 +21.10 + 6138.54 K 5 Solving, we find K,=: 6.08 K 2 = + 6.20 K :i = -1.81 Substituting these values in the equations of correlatives, we, obtain the corrections to the observed directions given in the column "Correction by adjustment" of the table of observed and adjusted directions. The quadrilateral 1 325 furnishes the side equation sin 315. sin 235. sin 521 = sin 531. sin r>23. sin 215 from which we derive the equation of condition 0= 324.5 2.5 (I) + 25.2 () 9.3 (:;) VI. The quadrilateral 3245 furnishes the side equation sin 235. sin 425. sin 543 = sin 523. sin 542. sin 435 from which we derive the equation of condition 0= + 342.4 29.7 (g) + 26.7 (=) 5.0 (J) OBSERVATIONS OF THE ECLIPSE OP AUGUST 7, 1369. The equations of conditions VI. and VI J. give rise to the following Equations of correlatives. 53 V a,K, & (f) 2.5 (I) - 9.3 + 26. 7 (3) + 25.2 - 29.7 (S) - 5.0 The resulting normal (-([nations are = 324.5 + 727.8 K, + 342.4 996.8 + 1020.0 K, Solving, we lind K, = + 0.994 K 2 = + 0.400 Substituting these values in the equations of correlatives, we obtain the corrections to the observed directions given in the column "Correction by adjustment" of the table of observed and adjusted directions. The quadrilateral .'3407 furnishes the side ('([nation sin 340. sin 730. sin 074 = sin 034. sin 073. sin 740 from which we derive the equation of condition ()= -57.3-0.4(5)- 1.11 () + 1.2(<) f 0.1 (I) VIII. The equation of correlative is: The normal equation is Solving, we Hud 0= 57.3 + 3.05 K, K, =+18.8 Substituting this value in the equation of correlative, we obtain the corrections to the observed directions given in the column "Correction by adjustment" of the table of observed and adjusted directions, Applying the "Corrections by adjustment" to the observed directions, we obtain the adjusted directions, by means of which the whole triangulation has been computed, as follows the lengths of the sides being given in meters : 54 REPORT OF PROFESSOR HARKNESS. No. Deuomiuation. Observed angles. Corr. by adjust. Planr angles anil ilislauiT'S. Logarithms. North Base South Rase o / // // 31 1.72 2. 497923 I. East Signal '. . North Base South Base East Signal South Base East Signal North Base ... 40 38 28.4 55 10 26.2 84 11 16.7 13.2 6.0 + 7.9 40 38 15.2 55 10 20.2 -1 11 24.6 306.66 480.76 0. 1*623* 11. 1114276 9.99776: 1 , 2. 598437 2. 681924 314 72 2. 497923 II. West Signal North Base South Base 62 34 50. 31 20 59. 2 86 4 56.2 15.0 30.11 0.4 62 34 35.0 31 20 29. 2 86 4 55.8 1*4 42 0. 051770 9.71611* 9. 998984 2 265811 , 353. 73 2. 548677 III. East Signal South Base West Signal . . . East Signal South Base West Signal South Base West Signal East Signal 6 38 15.8 3 4 36.8 170 16 12. it + 22. 8 + 24.2 + 7.5 3116. 6* 6 38 38. 6 3 5 1.0 170 16 20.4 184.43 579. 29 2.59*137 0. 936663 8. 730727 9.387798 2. 26,'i*-:7 2.762898 West Signal North Base . . 353. 73 2. 548677 IV. East Signal West Signal - , North Base East Signal North Base 37 33 51. 6 55 56 34.2 86 31 25. 4 - 37.4 - 37. H - 3(5.0 37 33 14.2 55 55 56. 4 .-d :;o in. i 1-0.76 0. 215021 9. 918228 9.999196 2. 681926 East Signal West Signal 579. 29 2. 762894 East Signal West Signal 579. 29 2. 762896 V. Court-house East Signal West Signal Court-house West Signal Court-house East. Signal 68 32 33. 1 *<> 2 51.2 + 21.* + 12.4 25 23 5.-'. 2 68 32 58. 2 *6 3 3. (i 1257. 01 1347. 35 0. 367616 9.968825 9.99*116* 3. 099337 3. 129480 East Signal South Base . 396. 08 2. 598437 VI. Court-house East Signal South Base Coiirt-hoiiHO South Base Court-house East Signal 65 27 56. 6 97 33 .111.2 + 0.6 + 6.2 16 58 7.4 65 27 57.2 97 33 55. 4 1236. 47 1347. 35 0. 534841 9. 958! N 15 9.990203 I!. 092183 3. 1294*1 North Base West Signal 353.73 2.54*677 VII. Naval Observatory . North Base West Signal .......... Naval Observatory West Signal . . Naval Observatory North Base . . . 13 31 15.8 107 34 35.0 + in.:. + 21.6 r,s r,:; 2". 1 13 31 35.3 107 34 56.6 96. 63 393. 85 0.067431 9.3691120 ftttWU 1.9*5128 2. 595330 OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 55 No. 1 iriHiinination. Ol) served angles. Corr. by adjust. Plane angles and distances. Logarithms. Kast Si-nial West Signal o / // // f>79 29 2 762894 Naval Observatory 14 8 54 6* 611835 VIII. Ka.-l Signal West Si-nal 2 20 20. 8 ifi:i :u ' 2 8.4 1C 2 2 20 12. 4 163 30 53 8. 610374 9 4 r > ->( Mi"i Naval Observatory West Signal Naval Observatory East Signal . 96. 63 672. SO 1.985103 2.H27694 West Signal Court-house .... Litehticld < >bservatory 71 1 26 :> j_ 45 o 1257. 01 71 2 11 5 3. 099337 024^35 West Signal 74 47 43 3 74 47 '!5 6 <) 984521 IX. ( 'cinrl-lioiisc Litchfield Observatory Conrt-b.ouse . l.itehlield Observatory West Signal . 3-1 10 12.9 1282. 61 746. f.2 9. 749469 3. 108093 2. 873041 Kast Signal West Signal 579 29 2 762896 Litchl'ield ( (bsrrvatorv 32 22 27 271284 X. East Signal West Signal Litelilield Observatory West Signal . Litelilielil Observatory East Signal 136 21 :{"). 9 11 1") 7.9 + 29.1 + 20. 1 136 22 5. 11 15 28.0 746. 52 211.21 9. 838864 9. 290532 2. 873044 2. 324712 In the triangle Nnvsil Observatory, West Signal, Court bouse, we have Plane angles and distances. Logarithms. Naval Observatory West Signal . West Signal Court-house . . . Angle at West Signal 96.63 1257. 01 110 26 3.4 1.985115 3. 099337 From which we find Angle at Naval Observatory . . Angle at Court-house . 1)5 33 10.3 4 46 3 Naval Observatory Court-house . 1293. 91 3. 111905 For the determination of the azimuth of the sides of the triangles we have the following obser. various of the sun, made near the time of its setting: August 9, 1889. Theodolite placed over West Signal Chronometer, Negus 1319 which is 6 h IS'" 17-vs fast of l(i,-i,l mean time. 56 REPORT OF PROFESSOR HARKNESS. Telescope direct. Object. Horizontal circle. Transit of sun's Vernier A. Vernier B. Court-house . . Snu .... Sun .... Sun .... Court-house . . Means. O III 360 84 20 40 85 6 .30 21 30 7 30 2d limb . 1st limb . /I. III. X. 12 7 '.I * 31 84 44 2 12 7 51.5 360 Telescope reversed. Court-house . . Sun .... Sun .... Sun .... Court-house . . Means. 360 86 18 85 58 19 59 1st limb . 2d limb . !> ic, :, 17 -JH 86 8 30 12 16 42.5 360 For the reduction of tbese observations I have made use of the formula tan M hill n COS / tan A = tan t. cos Sill M) where A is to be taken greater or less than 180, according as t is greater or less than A = azimuth of object, counted from the south around by the S = declination of object. t = hour angle of object. <p = latitude of place of observation. We therefore have Telescope direct. Telescope reversed. 7i. w. x. /I. HI. K. Equation of time .... t . . - 5 9.5 5 44 24.2 - o 5 9.4 5 53 15. 3 ci + 1538'40. " + 1538'34." t + 41 35 36. i 41 I!.", ;j(j M '. . . (<t> M) + 76 21 5. 34 45 29. + 84 3. 42 24 27. 99 21 5. 100 4f> 21. Reading of horizontal ciivle . 84 44 2. 86 H 3d. South point of circle . 345 22 57 345 23 9 Reading to Court-house . . 360 360 Azimuth of Court-house . . 14 37 3 14 36 51 OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 57 The azimuths of such other of the sides as were required, together with the differences of lati- tude and longitude, have been computed by means of the formula* d L = K. B. cos Z + K 2 . C. sin 2 Z + h 2 D A 1 . K. sin Z cos L 1 _ d Z = d M. sin In which N. arc 1" ,_ tan L ~~ 2 N. R. arc 1" \ = K. B. cos Z, or first term. R. arc 1" f e 2 . sin L. cos L. arc 1" (1 e 2 . sin 2 L)| a.(l e 2 ) (1 e 2 . sin 2 L) f (1 a equatorial radius of the earth = G377397.1G meters. b = polar radius of the earth = 635G078.9G meters. I*- =v : = 0.08169083 K = the given geodetic distance, in meters, between two trigonometrical points; L = the given latitude of the first point ; M = the given longitude of the same ; Z = the given azimuth of the second point as seen from the first : the azimuth being counted from the south around by the west ; L 1 , M 1 , Z' = the required latitude and longitude of the second point, and the azimuth of the first point as seen from it; dL, <Of, ZZ = the required differences iu latitude, longitude, and azimuth of the two points, expressed in seconds of arc ; so that L'=L +dL Z l = Z +(1Z 180. Taking the values of A 1 , B, 0, and D from the Coast Survey tables, the following are the results of the computations : Azimuths of sides. West Signal to Court-house Court-house to West Signal . . . Court-house to Naval Observatory Naval Observatory to Court-house Court-house to Litclifieltl Observatory Litchfield Observatory to Court-house 14 36 57. 194 36 47. 9 190 36 1.6 10 36 8.4 228 47 0. 8 48 47 28.4 The West Signal was 39".43 north, and 13".70 = S .913 east of the Court-house. The Naval Observatory was 41".23 north, and 10".28 = O s .685 east of the Court-house. The Litchfield Observa- tory was 27".40 north, and 41".66 = 2 S .777 east of the Court-house. 8* ' Extracted from the United States Coast Survey Report for 1860, p. 363. 58 REPORT OF PROFESSOR ITARKNESS. GEOGRAPHICAL POSITION OF THE COURT HOUSE DOME. The positions of all the temporary observatories must finally depend upon, and be referred to, the Court-house dome, for the determination of which we have the following data : In a letter to Commodore B. F. Sands, United States Navy, dated November 1, 18611, Professor J. E. Hilgard states, that the office reductions of the observations made for the determination of the position of the Coast Survey station at Des Moines have not yet been completed, but that the field computations give Latitude = 41 35' 2".08 Longitude = l h 29 m 58 N .29 west of Cambridge. The reduction from the station to the center of the Court-house dome is, in latitude + 1".27, and in longitude + O s .05. To refer the difference of longitude to Washington, I have employed the value of Cambridge Washington obtained from the joint observations of this observatory and the United States Coast Survey in June, 1867, namely, O 1 ' 2:5"' H S .(IS + O.04. My own observations, given in the previous pages of this report, place our temporary observa- tory at Des Moines in Latitude =41 35' S-^'.O 0".!K! Longitude = 1" G 1 " 1 8 .05 O s .05 west of Washington. On the evening of August 7, while 1 was exchanging longitude signals with the observatory in Washington, Professor Newcomb and Dr. Peters came to the telegraph office and compared their chronometers with the Washington clock. From these comparisons Professor Newcomb finds for the Court-house dome Longitude = I 1 ' 6"' 16 S .67, and Dr. Peters finds for the Litchfield temporary observatory Longitude = I 1 ' 6'" 14 S .02, in both cases counting from the dome of the observatory in Washington. Applying to these values the geodetic differences of latitude and longitude found from the tri- angnlation, we get for the Court-house dome Latilndt'. Longitude. Authority. o / // ll. III. X. 41 35 3. 3 1 6 17. 26 U. S. Coast Survey. 41 34 54.7 16.74 Harkncss. 1C. 117 Newcomb. 16.80 Peters. the longitude being measured from the center of the dome of the United States Naval Observatory in Washington. I am rather stiqirised at the large discrepancy between the Coast Survey observers and myself. On that account I will defer all further discussion as to the position of the Court-house until I make my report on the reading off and discussion of the photographs taken during the eclipse, hoping that by that time the final results of the Coast Survey observations may be avail- able. HEIGHT OF THE DIFFERENT STATIONS ABOVE THE SEA. Colonel J. W. Otley gave me a memorandum stating that the lines of level run for the Des Moines Valley railroad show that its track at the depot in East Des Moines is 310 feet above the Mississippi River at Keokuk. The Mississippi River at Keokuk is 450 feet above the level of the ocean. Hence the railroad track at the depot in East Des Moines is 7(i(i feet = 233.4 meters above the level of the sea. Setting up the theodolite at the Des Moines Valley railroad depot, the axis of its vertical circle being 4.5 feet = 1.37 meters above the track, I measured the zenith distance of the ball on the finial of the Court-house dome and found it to be 87 41'; the distance from the theodolite to the Court- house being 3,700 feet = 1,128 meters. OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1809. Setting up the theodolite at the West Signal, with the axis of its vertical circle 1.37 meters above the ground. I measured the following x.enith distances: o / Ball mi linial of Court -house .dome - 88 38 Floor of Litchtield Observatory 89 47 Floor of Naval Observatory 88 16 For the reduction of these observations I have employed the formula Difference of level = K. cot (A 0.01356 K) in which K is the distance iu meters between the two stations, A is the observed zenith distance, and (0.01350 K) is seconds of arc. The resulting elevation above the sea of the different stations is as follows: Elevation. Object. Meters. Feet Cmn t-lionse dome .... 280. 5 920.2 Ground at West Signal . . - 249.0 816.9 Naval Observatory floor . 253.3 831.0 LitrhlirM Observatory floor 253.2 830. 7 MISCELLANEOUS WORK DURING THE ECLIPSE. Before describing the observations made during the eclipse, I must not omit to mention the kind- ness and forethought of his honor J. H. Hatch, mayor of Des Moines, who, without any solicitation on our part, oil the afternoon of August 7, sent us two special policemen, Messrs. Thomas French and - Walker, to keep spectators from crowding too closely around our observatory. They did their duty most efficiently, preventing the occurrence of any noise in the neighborhood, and our thanks are due both to Mayor Hatch and to them. As I had decided to rest the astronomy of the eclipse entirely upon the readings to be obtained from the photographs, I attached very little importance to the making of optical observations of the times of contact. Nevertheless, as I did not expect to be otherwise employed at the beginning and ending of the eclipse, I at one time contemplated observing the first and last contacts by means of my three-inch telescope, but abandoned that plan for a reason which will presently appear. The course which seemed to me to afford the means of obtaining the greatest accuracy in deter- mining the beginning of the eclipse from the photographs, was to commence taking pictures about thirty seconds before the predicted time of lirst contact, and to continue taking them at as short intervals as possible, until the moon was well on to the sun. Upon mentioning this plan to Dr. Curtis he readily agreed to put it into practice, and a few trials showed that, with the number of baths and assistants at his disposal, he could take seven or eight pictures in about two minutes, after which a delay of two or three minutes would occur before fresh plates could be sensitized. Owing to the great length of the photographic telescope, it was found impossible to remove one sensitive plate and insert another without somewhat disturbing the pointing of the instrument, and thus rendering a new pointing necessary. When taking pictures at the rate of one per minute, Dr. Curtis found no difficulty in making the pointings himself; but in order to take four per minute, his whole time was required for the insertion, timing, exposure, and removal of the plates, and there- fore, at his request, I made the pointings of the telescope during the time that pictures were being taken at such short intervals. As it was necessary to take pictures rapidly, not only at the begin- ning of the eclipse, but at the end also, and as during the totality I was engaged with the spectro- scope, I was precluded from observing the time of any of the contacts. After the first two minutes of the eclipse 1 was relieved from the photographic telescope, and 60 REPORT OF PROFESSOR HARKNESS. at once proceeded to attach the spectroscope to my three-inch telescope, and to place and adjust the necessary counterpoises. When the eclipse had so far progressed as to reduce the sun to a crescent, with the assistance of Professor T. H. Saft'ord I adjusted the needle in the finder so that when its point fell upon a horn of the crescent the image of that horn fell accurately within the jaws of the spectroscope slit. This, with some other little matters, occupied my time till within three minutes of the totality, when, according to previous arrangement, I called Professor Eastman, who was to assist me in making the spectroscope observations by placing and keeping the needle point of the finder successively upon the different objects to be examined. THE SPECTROSCOPE OBSERVATIONS. It seems to me that one of the desiderata in spectroscopic observations of the sun during total eclipses, is to penetrate as low down towards the photosphere as possible. In order to accomplish this, I placed the slit of my spectroscope parallel to the moon's path, and clamped- it in that position, and so it remained during all my observations. Professor Eastman's eye was at the finder, and mine at the spectroscope, at least a minute before the commencement of totality, but he saw no prominences. Presently the sunlight disappeared like the snuffing out of a candle, and simulta- neously a suppressed, but very audible, "Oh, oh," arose from the spectators in the neighborhood. Instantly he placed the needle point on the prominence marked Fig. 2. 1 on Fig. 2, and I recorded its spectrum as rapidly as possible. Then we passed on to the prominences marked 2 and 3, and their spectra were successively recorded in like manner. Next I asked him to give me the corona, and he placed the needle point at c 1 . No spectrum appearing, I asked him to try another place, and he placed the needle at c 2 . Still nothing was visible, and, raising my head from the instrument for the first time since the commencement of the totality, I remarked, "Can't see any spectrum; don't believe we will get any." "Oh, yes, we will," said he. At that instant it struck me that perhaps the slit was too narrow, so I opened it a little, and then again placed my eve at the instrument. In the meantime he had put the needle point on a very bright part of the corona, marked <? in the figure, s and I at once saw a continuous spectrum about as bright as that given by the full moon on a clear night. Remembering that the observers in India, in August, 1868, had said that the corona gives a continuous spectrum with absorption lines, I looked very carefully for them, but to my great sur- prise I could see none, and I am perfectly satisfied that none were visible in my instrument. On the contrary, I saw an absolutely continuous spectrum, crossed by a single bright line, whose posi- tion was recorded. Once more raising my head from the instrument, I glanced upward to the sky and saw the moon encircled by the corona, and ac<x>nipauied by one remarkably large prominence, which was attached to the lower limb of the sun. I was well aware that the red prominences are sometimes visible to the naked eye, but this one was so exceedingly conspicuous that it could not fail to attract the attention of the most careless observer. Almost without thinking what I was doing, I asked Professor Eastman to point the spectroscope to it. He replied, "You have had it already." "Never mind, give it to me again," said I. He did so, and, as it is the prominence marked 3 in the figure, I have recorded its spectrum in the column headed 3 2 iu the table below. Professor Eastman then looked down to the chronometer in order to take up its beat for the purpose of noting the end of the totality. As he did so, I glanced into the finder so that I might get some idea of the appear ance of a total eclipse as seen through a telescope of small power. My view of it may have lasted five or ten seconds, certainly not more, yet the magnificence of the spectacle is so indelibly impressed upon my memory that it will be years ere I forget it. When he looked up from the chronometer I replaced my eye at the spectroscope, and asked him to give me another prominence. He put the needle point on the one marked 4 in the figure, and while I was yet engaged in recording its spec- trum there came a sudden burst of light, and Professor Eastman withdrew his eye from the finder, OBSERVATIONS OP THE ECLIPSE OF AUGUST 7, 1809. 61 exclaiming, "All over." It was too true. The event, for the proper observation of which we had traveled so far, and spent so much time, aud thought, and money, had come and gone, and now it remains for the scientific world to judge whether or not we made the most of our opportunity. Professor Eastman at once sat down and made a sketch of the corona and prominences as they appeared to him in the finder, numbering the prominences in the order in which he had given them to me in the spectroscope, and also marking the places on the corona at which he had pointed. I had recorded the spectrum observations myself, using for that purpose a small memorandum book, writing down the figures without looking at the page, arid recording only one spectrum at each open- ing of the book that is, when I had recorded one spectrum I always turned the leaf before record- ing another thus devoting two whole pages to each observation. Such being the state of the case, all that was necessary in order to identify each spectrum with the prominence to which it belonged, was for me to mark the records of the spectra in my note book with the same numbers as those employed by Professor Eastman on his sketch, and that I did at once ; therefore I think no question can ever be raised as to the prominences to which the spectra belonged. At the time of making these observations the impression left on my mind was that the spectra given by the different prominences differed from each other, not only in the number of the lines, but in their position also. It was not till four hours after the eclipse that I had time to compare them with each other, and when I did so, arranging them as in the table below, great was my surprise to find that the difference between the different prominences was only in the number of lines, and not in their position at all. Before passing to the consideration of the lines, however, it will be best to mention some particulars relative to the adjustments of the spectroscope, and the method pursued in making the observations. Some minutes before the beginning of the totality the micrometer scale was so adjusted that its fiftieth division coincided exactly with the mean of the two sodium lines which together form the line D ; and the slit was opened to such a width as to give fine, sharp definition of all the lines. The instrument remained in that condition till the observation of the spectrum of the corona, before which the slit was opened a little wider. After that none of the adjustments were altered in the slightest until the next day. Immediately after the end of the totality the scale reading of the line D was tested ; first by observing the position of the black line in the solar spectrum, and then by placing the Hame of an alcohol lamp, whose wick contained a little common salt, before the object- glass of the telescope and observing the position of the resulting bright line. In both cases the reading was exactly fifty divisions, thus proving that the instrument had kept its adjustment during the observations of the prominences and corona. Then the following readings of the positions of some of the lines in the solar spectrum were taken : C 36.2 D 50.0 E 67.9 b 71.5 F 84.8 115.0 116.0 G 117.8 After that the spectroscope was detached from the telescope. Next morning, before any of the adjustments had been altered in the slightest, a sodium flame was put before the slit of the spectro- scope and the width of the resulting bright line was observed to be 0.8 -of a scale division. From the angular value of one division of the scale, together with the focal length of the collimating lens of the slit, it can easily be shown that- when the width of the bright sodium line is one division, the width of the slit is 0.0037 of an inch. Therefore, at and after the observation of the spectrum of the corona the width of the opening of the slit was 0.0030 of an inch ; in observing the spectra of the prominences before that it was a little narrower. As my instrument gives a spectrum about 330 minutes in length, the whole of which is visible at once in the field of view of its telescope, it is admirably adapted for rapid work. But when the telescope is adjusted to give the best possible definition of the lines near D, those near H, although still quite distinct, are nevertheless slightly out of focus, and by moving the eye across the eye-piece their scale reading can be made to vary a little. To have adjusted the focus accurately on each line observed during the eclipse would have involved an expenditure of time not for one moment to be 62 REPORT OF PROFESSOR HARKNESS. thought of, and, as each scale division corresponds to somewhat less than two minutes, I therefore judged it best to observe as many spectra as possible, noting the position of each bright line to the nearest half of a scale division only, and trusting that, from the closely approximate positions thus obtained, all the lines might be found at any time after the eclipse with a sufficiently powerful instru- ment. Now let us pass to the consideration of the observations. They are given in the table below, the first column of which contains the letters of such of the lines as are so designated ; the columns headed 1, 2, 3 1 , 3 2 , and 4, contain respectively the spectra of the prominences marked 1, 2, 3, and 4> in Fig. 2, the column headed 3 1 containing the record of the first, and that headed 3 2 the record of the second spectrum observed from the prominence 3 ; the column headed "Corona" contains the reading of the bright line in the spectrum of the corona. 1 2 3' Coroiia. 3- 4 Meau. Kirch, scale. \Vav.j length. c 46.0 37.0 36.5 36.0 36.0 36.3 693 656.9 D 50.0 50.5 50.0 50.0 50.1 1007 589.4 67.5 67.0 67.0 66.5 66.5 67. r> 67. (1 1497 531 1. . 70.5 . 70.5 Kill 520.1 F 85.0 . . si. 84.5 84.5 2069 Mr. e - - - - - 114.0 1 1 1. 5 114. '.> 8776 436.9 The number 40, recorded on the line C in column 1, is evidently a misreading of ten divisions. It should doubtless have been 3G. Making this correction, and bearing in mind that the readings were made at a glance, te the nearest half division only, without stopping to verify them, I think it will be admitted that all the numbers on any one horizontal line of the table are sufficiently near to each other to warrant me in assuming them to be readings of one and the same bright line. In other words, during the whole of the totality I only observed six lines; the double line D being counted as a single line because it so appeared to inc. I have therefore taken the mean of the num- bers on each horizontal line, and placed them in the column headed "Mean." These I consider to be the observed scale readings of the bright lines, and in the columns headed " Kirch, scale " and " Wave length," I have given the corresponding readings of Kirchhotf 's scale, and the wave lengths expressed in milliouths of a millimeter. Now let us examine the position of each prominence at the time its spectrum was taken. The spectrum of 1 was observed as soon after the beginning of the totality as possible, but a glance at Fig. 2 shows that it lay very far from the path of the moon's center, and therefore its base was not visible. It gave four bright lines. 2 was next examined.- It lay almost exactly in the path of the moon's center, but by this time she had advanced so far that probably it was not visible more than half-way down to its base. It gave three bright liues. Then the t-elescope was pointed at 3, which, being on the southwestern limb of the sun and distant from the path of the moon's center, had only just begun to be much uncovered. Its summit was all that was visible, and it gave but two bright lines. After spending some time on the corona, 3 was again examined. As the moon had moved forward considerably the prominence was uncovered much further down towards the sun, and now it gave no less than six bright lines. Finally 4 was pointed at, and as it lay almost exactly in the path of the moon's center, and the totality ended while it was yet under examination, the spectro- scope must have penetrated down to its very base. I recorded five bright lines from it, but I am not certain that there were no more, because I was not done with it wheu I was stopped by tin- flood of returning sunlight. The first thing that would be likely to strike a person on looking at the observations is that no two prominences gave the same spectrum ; but I think it is now evident that this does not indicate any difference of constitution among them. On the contrary, the num- ber of lines visible seems to depend solely on the part of the prominence examined. If we take the spectrum from near the summit we get but few lines ; if we take it lower down we get more lines, but those that we found at the top are still there ; if we take it near the base all the lines we had before remain, and, in addition, some new ones appear. Therefore I infer that these observations OBSERVATIONS OP THE ECLIPSE OF AUGUST 7, 1869. 63 indicate that all the prominences possess nearly, if iiot precisely, the same physical constitution, but that that constitution undergoes a gradual change from their bases toward their summits. If such is the case, then, when the spectrum of a prominence is examined with the slit of the spectroscope perpendicular to the limb of the sun, the bright lines should appear of different lengths. This applies to my observations of the prominences 2 and 4, but whether or not they gave lines of dif- ferent lengths I am unable to say. I remember distinctly that some of the prominences did do so, but unfortunately I made no memorandum which will enable me to identify the particular ones. The next question which presents itself is, what are the substances which gave rise to the observed bright lines? In order to identify these lines in the most certain manner possible, I was very anxious to observe with my instrument the spectra of hydrogen, iron, and magnesium, but unfortunately I did not succeed in obtaining a sufficiently powerful induction coil. 1 am therefore obliged to resort to the published results of other investigators. Professor W. Gibbs,* on the authority of Pliicker, gives for the wave lengths of the hydrogen lines, H = 653.3, Rft = 484.3, H^=433.9 ; and on the authority of Angstrom, H/?=1797.3, H^=1604.3. H and lift are known to coincide respectively with Fraunhofer's C and P, for which I have adopted the wave lengths 050. 8 and 486.5. In order to render Pliicker's values identical with these, his II must be multiplied by 1.0054, and his 11,5 by 1.0045. Multiplying his HJ- by this last quantity, it becomes 435.9, which I shall consider as the result of his observations. Angstrom's wave lengths are, given in j-ujnlooou ^ a P ai 'i s inch, and in order to reduce them to millionths of a millimeter, I have assumed 1 Paris inch = 27.0700 millimeters. They therefore give, H,S = 480.5, 11^ = 434.3. Taking the .mean of Plh'ckcr's and Angstrom's meas- ures, we have for the wave lengths of the hydrogen lines II = G5G.S H/S = 48G.5 H r = 435.1 Assuming the wave lengths of the lines sodium ft and to be respectively 590.53 and 589.88, Kayett gives as the wave length of the yellow bright line in the solar spectrum, 588.27 = 1016.8 of Kirchhoff's scale. Throughout this report I have adopted Na. ft = 590.04, Na. a = 589.43. It there- fore results that the wave length of the Yellow bright line = 587.9 From a paper "On the Spectra of some of the Chemical Elements," by Mr. William Huggins,| I have extracted the following positions of certain bright lines in the spectrum of iron : Huggins's scale. Wave length. 1560 530.7 .1574 529.4 1582 528.8 The lines 1560 and 1574 are quite faint, but 1582 is very bright. I have made use of Professor W. Gibbs's tables to convert the readings of Mr. Hnggins's scale into wave lengths. I have not any table of the spectrum of magnesium, but its principal lines are known to coin- cide with the components of Fraunhofer's line 6, the wave lengths of which, as deduced by Profes- sor W. Gibbs from Ditscheiner's and Angstrom's measurements,!] are as follows: 518.73 517.70 517.15 American Journal of Science, [2,] XXXIX, 217. } Philosophical Transactions, 1864, p. 139. t Comptes Rendus, LXVIII, 320, February, 1869. American Journal of Science, [2,] XLVII, 194. II American Journal of Science, [2,] XLIII, 1, and XLV, 298. 64 REPORT OF PROFESSOR HARKNESS. For convenience of reference the results are collected in the following table, the first column of which contains my observed wave lengths of the various bright lines given by the corona and prom- inences, together with the possible error of each wave length, deduced upon the supposition that the observed scale reading of any line may be in error to the extent of half a division ; the second column contains the wave lengths found above for the bright lines in the spectra of certain chemi- cal elements : Wave lengths of bright lines. AV:ivi> lengths of chemical ele- ments. 656. 9 3. 2 656. 8 Hydrogen. 589. 4 2. 1 587. 9 Unknown, (sodium f) 530.71 530.0 1.4 529. 4 I Iron. 528. 8 J 520.1 1.4 518. 7 Magnesium. 487.5 1.0 486. 5 Hydrogen. 435. 9 0. 7 435. 1 Hydrogen. Owing to the very moderate dispersive power of my spectroscope the iron lines 528.8 and 529.4 would certainly coalesce, and 530.7 would probably coalesce with them, and appear as a single rather thick line, which was what I actually sa\v.* Bearing in mind what is already known of solar physics, I think there can scarcely be a doubt that the bright lines in the prominences were pro- duced by the substances whose names stand respectively on the same horizontal lines with the observed wave lengths in the table above. The identification of the lines is therefore complete. Physical constitution of the corona. On this subject many different theories have been proposed, but they may all be divided into three general classes: 1. Those which attribute the formation of the corona to the passage of the sun's rays through the earth's atmosphere. 2. Those which attrib- ute its formation to the passage of the solar rays through a supposed lunar atmosphere. 3. Those which consider the corona as an envelope of some kind surrounding the sun. Against theories belonging to the first class there are two objections which seem to me to be fatal. The moon's shadow, at the point where it enters the earth's atmosphere, usually has a diame- ter of one hundred miles or more, and if it were possible for an observer placed within that shadow to see the illumination of the atmosphere outside of it, the appearance presented would be that of a halo having an interior diameter much greater than the size of the moon. At the commencement of the totality the moon would be within, and tangent to, this halo, and as the eclipse progressed she would move across its interior till she finally reached its other edge, at which instant the totality would end. It is almost needless to say that no such phenomenon has ever been seen, the only known effect of the illumination of the surrounding atmosphere being to produce a blush of light in the distant horizon. Besides, as the illumination of the surrounding atmosphere is due to ordinary sunlight, if it is the cause of the corona its spectrum should show Fraunhofer's lines, while my observations prove that it does not do so. I looked specially for them, but could see none, although the spectrum was sufficiently bright and the width of the slit was only 0.0030 of an inch. Against theories belonging to the second class there are equally fatal objections. For many years astronomers have exhausted all their ingenuity in devising methods for the detection of a lunar atmosphere, but as yet without success. Mr. Huggins's observation of the occupation of e Piscium, on January 4, 1865, through the spectroscope,! is probably the most delicate optical test that can be applied, but even it failed to show any trace of such an atmosphere. I am aware that the brightening seen along the limb of the moon on photographs of solar eclipses has been attributed by some to the effect of a lunar atmosphere; but Mr. Airy has shown f that, even if such an atmo- * I do not wish to be understood as stating that the bright line in the corona is either double or triple. I only assert that, so far as my observations are concerned, such may be the case ; and that, at all events, I think it will be found to coincide with one, or more, of the three iron lines in question. t Monthly Notices, Royal Ast. Soc., XXV, 60. } Monthly Notices, Royal Ast. Soc., XXIV, 13. OBSERVATIONS OB' THE ECLIPSE OF AUGUST 7, 1869. 65 sphere existed, it could not produce this effect; and Dr. Curtis shows in his report on the eclipse under discussion that it is due to the diffraction of the sunlight caused by the moon's limb. In short, there is not a shadow of reason to believe that any such thing as a lunar atmosphere exists ; but if it did, and the corona was due either to reflection or refraction of the sunlight by it, then the spectrum of the corona should show Fraunhofer's lines, which, as I have already stated, is not the case. An examination of the photographs of totality, fac-similes of which are given in Plates X and XI, shows that as the moon advanced the corona was progressively covered ; and this, taken in connection with the spectroscope observations, forces us to conclude that it must be an envelope of some kind surrounding the sun. It has been objected that it cannot be a solar atmosphere because its form is too irregular. Plates IX, X, XI, and XII show that during the present eclipse its gen era! outline was trapezoidal, the angles being in middle latitudes ; in other words, it did not extend so far from the body of the sun either at the equator or at the poles as it did about latitude 45. Observations of the barometer made at the level of the sea show that the earth's atmosphere has a very similar form, which, I think, is a sufficient answer to the objection. It has also been objected that if the corona is an atmosphere surrounding the sun, it should reverse the bright lines which can always be seen in the chromosphere by using a spectroscope of sufficient dispersive power. This is somewhat difficult to answer. The general appearance of the spectrum of the corona, as I saw it, is very well represented on Plate V. The brightness of the continuous portion was about equal to perhaps slightly less than that of the spectrum which I get from the moon in the same instrument ; and I am perfectly convinced that there were no absorption lines. I looked particu- larly for them, and the light was sufficiently intense and the slit sufficiently narrow for me to have seen them if they had been present.* The bright line was tolerably conspicuous, but it did not stand out so glaringly as the bright lines in the prominences. So far as a single observation can be depended upon, it seems to me that this one tends to prove that the corona is a highly rarefied self-luminous atmosphere surrounding the sun, and that it is composed principally of iron in the state of incandescent vapor. Probably the selective absorption of the continuous portion of the spectrum is not sufficiently strong to do more than slightly dim, without actually reversing, the bright lines of the chromosphere. But with the bright line at 67.0 divisions of my scale the case is different. If I have rightly identified its wave-length, it does reverse the solar spectrum, for the rays whose wave-lengths are 530.7 and 528.8 are respectively identical with the dark lines at 1487.7 and 1508.6 of KirchhofFs map. It has very recently been suggested that the bright line in the corona probably coincides with one of the bright lines in the spectrum of the aurora, and that therefore the corona is nothing else than a permanent solar aurora. On the nights of April 15 and June 6, 1869, Professor Joseph Winlock observed the following bright lines in the spectrum of the aurora : t Mr. Huggins' scale. Wave length. 1280 (brightest) 557.1 1400 544.6 1550 531.5 1680 near F. 521.0 2640 near G. 463.9 Angstrom gives J for the wave-length of the brightest line in the aurora 556.7, agreeing very well with the result above. I found for the wave-length of the bright line in the corona 530.0, while Professor Winlock finds for one of those in the aurora 531.5. I scarcely think that the two are identical, but even if they are, although it may prove that the glowing gas, or vapor, is the same in both cases, it certainly does not prove that in the case of the corona the heating power is an elec- trical discharge, which is generally admitted to be the cause of the aurora. It is worthy of remark * It is now nearly certain that if hydrogen gas is gradually heated until it becomes luminous it will first yield a continuous spectrum, which, when the temperature becomes sufficiently intense, will suddenly change into the well- known spectrum consisting of three or four bright lines. May not the continuous spectrum of the corona be due to hydrogen which is much cooler than that forming the red prominences f tAmer. Journal of Science, [2,] XLVIII, 123. tPgg- Annalen, May, 1869. -9* 66 REPORT OF PROFESSOR HARKNESS. that the lines 1400 and 1680 of Professor Winlock's spectrum of the aurora .coincide respectively with the positions of an iron and a chromium line in Mr. Hnggius' tables. Have we iron vapor in the upper regions of our own atmosphere f Physical constitution of the red prominences. A glance at Plate V shows that all the promi- nences which I observed presented the bright line whoso wave-length is 530.0, together with a faint continuous spectrum ; but as those were dne.to the light radiated from that portion of the corona lying between me and the prominences, there remain only three hydrogen lines, one magnesium line, and the unknown line near that of sodium, which were produced by the prominences them- selves. These lines have all been frequently observed before, and it is also well known that the magnesium never rises very high above the chromosphere, but so far as I am aware the following- fact is new. At the base of a prominence we find all the lines, but as we ascend from the surface of the chromosphere we lose first the magnesium and the blue hydrogen line, then the green hydro- gen line, then the unknown yellow line, and only the red hydrogen line extends to the very summit of the prominence. This has a very important bearing on a remark by Mr. De La Hue,* who lays great stress on the fact that he found on one of his photographs of the total solar eclipse of July 18, 1860, the image of a prominence which he had not seen in his telescope. Hearing in mind that the red and yellow portion of the spectrum contains most of the luminous rays, while it is destitute of chemical ones, it will be evident that the spectroscope observations tend to prove that, owing to their summits not containing any chemical rays, the prominences will not appear so high on a pho tograph as they do when viewed in a telescope ; and also that any prominence which can be photo- graphed must be visible to the eye through a telescope of sufficient power, while there may be prominences perfectly visible to the eye which cannot be photographed. Tliis is in direct opposi- tiod to Mr. De La Eue's statement, but it agrees perfectly with Professor Eastman's observations of the present eclipse, for his sketch shows all the prominences which are to be found on the photographs. The question naturally presents itself, why do the hydrogen lines disappear successively in the manner indicated above 1 So far as we know it must be the effect either of pressure or of temper- ature. Under a pressure of 360 millimeters, and with a very intense spark, hydrogen gives a con- tinuous spectrum. At a somewhat less pressure the spectrum breaks np'into bands, H/3 and H/ being the broadest ; if the gas be considerably rarefied these bands become perfectly sharply defined lines. If the reduction of pressure be still further continued, the red line, H, gradually disappears, while H/J, though fainter, remains well defined. Hence the disappearance of the lines in the prominences cannot be an effect of pressure, and is probably due to decrease of temperature. The highest temperature procurable by artificial means is that yielded by the electric spark which will produce all the hydrogen lines. Next to it ranks the oxy hydrogen flame, the spectrum of which, and also that of the hydrogen flame, I was enabled to examine by the kindness of Brevet Lieutenant Colonel J. J. "Woodward, assistant surgeon United States Army. In both cases the result was the same. Only three lines were visible, namely : that of sodium and the lines calcium and /?. Not .the slightest trace of the hydrogen lines appeared. I therefore "conclude that the temperature of the summits of the red prominences is greater than that of the oxy-hydrogeu flame, which is about 2500 Centigrade = 4532 Fahrenheit, and less than that of the electric spark, the heat of which is entirely unknown. To recapitulate, the new facts developed by the spectroscope observations recorded in this report are I. The corona gives an absolutely continuous spectrum, crossed by a single bright line whose wave-length is approximately 530.0. II. In ascending from the chromosphere the hydrogen lines in the red prominences disappear in the order H^, H/3, Ha ; Ha being the only line found at the very summit of the prominences. III. The physical constitution of the red prominences appears to be the same in all. From these facts I consider the following conclusions highly probable, if they are not actually proved. A. The corona is a highly rarefied self-luminous atmosphere surrounding the sun, and, perhaps, principally composed of the incandescent vapor of iron. * Phil. Transactions, 1862, p. 404. OBSERVATIONS OP THE ECLIPSE OF AUGUST 7, 1869. 67 B. The temperature of the summits of the red prominences, at a distance of a hundred thou- sand miles from the sun's surface, exceeds 4500 Fahrenheit a heat more than sufficient to vaporize iron. SCALE OF TINTS. The scale of tints, with which the colors of the prominences seen around the sun during the totality were compared, is shown in Plate V, and is composed of the following pigments: a and b, pure carmine, c and d, carmine and cadmium, e, Vandyke brown, fandg, Van- dyke brown and cadmium. A, pure cadmium, i, sepia and cadmium. CONCLUSION, All my instruments and apparatus worked in the most satisfactory manner, and were I ordered to observe another solar eclipse I would make but two change* in my outfit. In place of the small pocket surveying instruments I would take, if possible, a five or six. inch theodolite ; and I would have my spectroscope altered so as to employ a collimating lens of shorter focus between the prism and the slit thus bringing the body of the instrument nearer to the telescope, and avoiding the use of such heavy counterpoises. In the examination of the corona and prominences, I believe that more spectra can be observed during the time of totality by having a steady and reliable assistant to point the finder, than if a driving clock is employed and the spectroscope observer makes the pointings himself. In view of the very great importance which the question of the physical constitution of the corona has assumed, I regret exceedingly that there was a failure in the use of my polarizing appa- ratus, and that I am unable to report any results from it. I shall at once proceed to design the large micrometer necessary for reading off the photographs taken by Dr. Curtis during the eclipse, and as soon as the instrument is completed I will make the measurements on the negatives, reduce and discuss the results, and place my report on the subject in your hands, so that it may be published without any unnecessary delay. I am, Commodore, most respectfully, \VM. HARKNESS, 1'rofennor of Mathematics, United States Navy. Commodore B. F. SANDS, U. S. N., Superintendent United States Naval Observatory, Washington, D. C. REPORT OF PROFESSOR HARKNESS. SCHEDULE A. Observations of the sun for Time, made at the temporary United States Naval Observatory at Des Moines, Iowa, by Prof. Wm. Harkness, U. 8. N., icith the Sextant Staekpole cfc Bro. No. 937, Mer- curial Artificial Horizon Ha. 1, and Chronometer T. S. & J. D. Negus No. 1.310. [NOTE. The barometer employed was an aneroid belonging to Prof. J. R. Eastman; and 0.38 of an inch must be subtracted from all its recorded readings in order to free them from constant errors.] SUN . . . JULY 23, 1869. SUN . . . JULY 23, ls(>9. Index Corr. E Index Corr., &c. On Arc = 6>. Off Arc = 4)i. Index Corr. E Index Corr., &c. On Arc = o. Off Arc = t)i. / a 29 10 30 20 O ' " 4 26 30 10 25 t ii 29 10 20 15 O ' " 4 26 10 10 10 + 2 9.6 + 10.4 t + 2 17.5 + 8.9 -f- 2 20 + 2 26. 4 Means Index Corr., &c. Q Refraction Parallax 2 Altitude. Chronometer. Means Index Corr., &c. Q Refraction Parallax 2 Altitude. Chronometer. O ' '/ 60 30 45 61 60 30 45 61 h. m. a. 1 55 35.0 56 15.1 56 55.6 58 23.6 59 2.9 59 42.3 O ' '/ 54 30 15 54 30 15 /I. !. 8. 11 6 3.2 ti 44. 7 23.5 8 50.5 9 31. 5 10 11.3 60 45 0.0 + 2 20.0 1 57 39. 1 54 15 0.0 + 2 26. 4 11 8 7.3 o Ther. 76.0 in. Bar. 29. 58 O ' /' = 69 58 49. 3 h. m. s. 7 33 20. 1 . + 6 10.6 60 47 20. 1 33.0 + 7.3 54 17 26. 4 1 44.5 + 7.5 Polar distance of object . . Local Apparent Time . . . Equation of Time .... Local Mean Time .... Time by Chronometer . . . Chronometer fast of Local M. T. Polar distance of Local Apparent T Equation of Timi Local Mean Time Time by Chromm Chronometer fast These observatu / " object . . =70 3 34. 4 h. in. s. ime .... 4 43 48. 7 ) -L R 11 9 . 7 39 30. 7 . 1 57 39. 1 4 49 59 9 rlrl 1 . . 11 8 7.3 . 6 18 8.4 of Lorn! M.T. . 6 18 7. 4 us wi'i- made after noon. These observations were made before noon. OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. SCHEDULE A Continued. 69 SUN .... JULY 23. SUN .... JULY 24. On Arc u. Off Arc = u'. On Arc = a. Off Arc = a 1 . t n ot" t it 29 20 20 30 ' " 4 25 40 40 45 Index Corr. + 2 17. 5 E + 7. 7 Index Corr + 2 27. 5 E +8.6 Index Corr., &c. + 225.2 Index Corr., &c. !+ 2 36. 1 2 Altitude. Chronometer. 2 Altitude. Chronometer. O ' II 47 45 30 15 47 45 30 15 h. m. e. 11 24 11.3 24 51. 8 25 31.7 27 0.5 27 38.5 28 20. 8 / II 52 30 45 53 52 30 45 53 h. m. s. 1 34 50.6 35 31.5 36 12.0 37 40.0 38 19.0 39 0.0 Means 47 30 0.0 Index Corr.,iVc. -f 225.2 11 26 15.8 Moans 52 45 o. Index Corr., &c. ; + 2 36. 1 1 36 55. 5 Thfi . 86. 8 O 1 II 70 3 43. 3 /I. III. 9. . 5 1 56.7 - + 6 11.2 .0 Thcr. 77. in. Bar. 29. 46 o" / /' = 70 11 11.2 h. Ml. 8. . 7 12 34.8 + 6 11 8 Q 47 32 25. 2 Kofi-action 2 1.2 Parallax -f- ~-7 Q '>> 47 36. 1 Refraction 1 49.8 Parallax -f- 7.6 Polar distance of object Local Apparent TimS Equation of Time Local Moan Time .... Polar distance of object . . Local Apparent Time .... Equation of Time Local Mean Time - 5 8 7. 9 7 18 46 6 Time by Chronometer . . . Chronometer fast of Local M. T. - 11 26 15.8 Time by Chronometer . . . Chronometer fast of Local M. T. 1 36 55. 5 6 18 7.9 . 6 18 8.9 These observations \vere made after noon. These observations were made before noon. 70 REPORT OF PROFESSOR HARKNESS. SCHEDULE A Continued. SUN .... JULY 26. SUN .... JULY 26. Index Corr. E Index Corr., &c. On Arc = a. Off Arc = u 1 . Index Corr. E Index Corr., &c. On Arc .= u. Off Arc = u 1 . t a 29 10 10 10 Q 1 II 4 26 10 25 50 26 10 i it 29 10 25 25 ' " 4 26 10 10 + 2 23. 4 + 12.0 + 2 16.6 + 12.0 + 2 35.4 + 2 28.6 Means Index Corr., &c. Refraction Parallax 2 Altitude. Chronometer. Means Index Corr., &c. n Refraction Parallax 2 Altitude. Chronometer. o ' " 67 30 45 68 67 30 45 68 h. m. s. 2 16 29. 5 17 10.0 17 50.6 19 19.5 19 58. 20 39.2 / II 68 67 45 30 A. in. s. 10 30 38. 4 31 19.5 31 59.2 67 45 0.0 + 2 35.4 2 18 34. 5 o Ther. 70. iw. Bar. 29. 52 O t H = 70 37 39. 1 A. m. s. . 7 54 12.0 -f 6 12 7 Ther. 81. in. Bar. 29. 49 O ' " = 70 42 13. 8 /I. HI. 8. 67 47 35.4 1 22.3 + 7.0 Polar distann of Local Apparent T Equation of Time Local Mean Time Time by Chrononi Chronometer fast These observatio object me Polar distance of Local Apparent T Equation of Time Local Mean Time Time by Chronom Chronometer fast These obiwrvatio abject - - me ... 8 24. 7 eter . . . of Local M. T. . 2 18 34. 5 Bter . . . .f l.orul M.T. - . 6 18 9.8 - as were made before noon. is were made after noon. OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 71 SCHEDULE A Continued. SUN .... JULY 26. SUN .... JULY 27. Index Corr. E Index Corr., &c. On Arc = a. Off Arc = u'. Index Corr. E Index Corr., <fec. On Arc = u. Off Arc = u<. o / " / // o / // + 2 16.0 + 11.3 + 2 18.3 + 13.0 + 2 27.9 + 2 31. 3 Means Index Corr., <fcc. U Refraction Parallax 2 Altitude. Chronometer. Means Index Corr., <fec. Q Refraction Parallax 2 Altitude. Chronometer. o / // 64 45 30 15 64 45 30 15 ll. III. 8. 10 36 33.0 37 12.8 37 52.5 39 20. 8 40 1. 5 40 41.0 / " 72 30 45 73 72 30 45 73 h. m. s. 2 30 41. 31 22.0 32 1.0 33 29. 8 34 9.7 34 50.0 64 30 0.0 + 2 27. 9 10 38 36. 9 72 45 0. + 2 31.3 2 32 45.6 O ' // = '70 42 17. 8 li. m. . . 4 14 ]5.5 _|_ 6 12 5 O / // = 70 51 18. 7 h. m. s. . 8 8 22. 8 - + 6 12.2 64 32 27. 9 1 25.8 + 7.1 72 47 31. 3 1 14.5 + 6.8 Polar distance of Local Apparent TJ Equation of Time Local Mean Time Time by Chronom Chronometer last These obser\ atio object me Polar distance of < Local Apparent Ti Equation of Time Local Mean Time Time by Chrouom Chronometer fast < These observatioi )bject me 4 20 28. 8 14 35 ?ter . . . jf Local M. T. . 10 38 36.9 jter . . . >f Local M. T. - 2 32 45.6 . 6 18 8.9 . 6 18 10.6 is were made after noon. is were made before noon. 72 REPORT OF PROFESSOR HARKNESS. SCHEDULE A Continued. SUN .... JULY 27. SUN .... Jri.V 2K. Index Corr. E Index Corr., Stc. On Arc = u. Off Arc = u'. Index Corr. E Index Corr., &c. On Arc = u. OH' Are (A i u 29 15 30 20 O ' '/ 4 26 5 1 II 29 20 30 30 ' a 4 26 10 111 + 2 18.3 + 13.7 + 2 13.3 + 11.3 + 2 32. + 2 24. 6 Means Index Corr., &c. B Refraction Parallax 2 Altitude. Chronometer. Means [nili-x (,'OIT., &e. a Refraction Parallax 2 Altitude. Chronometer. O i .11 74 45 75 15 74 45 75 (1 15 II A. m. a. 2 36 43. 8 37 25.0 38 5.9 39 34.5 40 14.5 40 55. o / a 64 30 45 65 64 30 (I 45 ()., (I h. m. . 2 9 58. 10 37.0 11 17.8 12 46.2 13 2<i. 2 14 6. 3 75 0.0 + . 2 32.0 2 38 49.8 64 45 0.0 + 2 24. 6 2 12 1.9 o Ther. 74. in. Bar. 29. 53 U / // = 70 51 22. 1 A. m. s. . S 14 26. 8 + 6 12. 2 Ther. HI. in. liar. 29. 58 ' II = 71 4 57.4- /(. Ml. 8. . 7 47 38.4 . + 6 11.2 75 2 32. 1 11.6 + 6.7 64 47 24. 6 1 28.2 + 7.1 Polar distance of Local Apparent T Equation of Time Local Mean Time Time l>y Clironnm Chronometer fast These observatio object me ... Polar dislanre uf Local Apparent T Equation of Time Local Mean Time Time by Chronom Chronometer fait These obsenalin object . . me 8 20 39 . 7 53 49.6 eter . . . of Local M. T. . 2 38 49. 8 eter . of Local M.T. . 2 12 1.9 . 6 18 10.8 . 6 18 12.3 us were made before noon. MS were made before noon. . OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 73 .SCHEDULE A Continued. SUN .... JULY 28. SUN .... JULY 28. Index Corr. E Index Con\, &c. On Arc = u. Off Arc = u'. Index Corr. E Index Corr., &e. On Arc = u. Off Arc = o,'. / // 29 10 10 10 o / // 4 25 50 26 25 40 / // o / // + 2 ::n. 4- 11.3 + 2 30. t' + 10. 7 + 241.3 + 2 40.7 Means Index Corr., &c. U Refraction Parallax 2 Altitude. Chronometer. Means Index Corr., &c. Q liVfi action Parallax 2 Altitude. Chronometer. O 1 II 65 64 45 30 65 64 45 (I 30 /I. lit. 8. 10 34 21.2 35 2.2 35 42.3 37 9.2 37 49. 5 38 30. 1 Q 1 II 62 61 45 30 62 61 45 30 A. m. 8. 10 42 24. 5 ' 43 4.5 43 44. 45 11.0 45 52. 46 32. 3 64 45 0.0 + 2 41.3 lit :i; -j:>. >' 61 45 0.0 + 2 40.7 10 44 28.0 O ' // = 719 52. 6 /i. m. s. . 4 12 4.4 . + 6 10. 7 Ther. 74. in. Bar. 29; 57 = 71 9 57.2 /I. 111. X. . 4 20 6.4 . + 6 10.7 64 47 41. 3 1 26.5 + 7.1 61 47 40.7 1 31.7 + 7.2 Polar distance of < Local Apparent Ti Equation of Time Local Mean Time Time by Clironom Chronometer fast These ohservatioi ibjcct - - me ... Polar distance of Local Apparent Ti Equation of Time Local Mean Time Time by Clironom Chronometer fast ( These observatim ibjeet me ;tcT . )f Local M. T. - 4 18 15. 1 . 10 36 25. 8 4 26 17. 1 iter . . . )f Local M. T. . 10 44 28.0 . 6 18 10.7 . 6 18 10.9 is were made after noon. is were made after noon. 10* 74 REPORT OF PROFESSOR HARKNESS. SCHEDULE A Continued. SUN JULY 29. SUN .... JULY 29. Index Con - . E Index Corr., &c. On Arc = a. Off Arc = <A Index Corr., E Index Corr., &c. Ou Arc = u. Off Arc = o>. i a 29 10 15 10 Q I II 4 26 25 50 55 i n ' " + 2 26. 6 + 10.9 + 2 26. 6 + 10.9 + 2 37.5 4- 2 37. 5 Means Index Corr., &c. Q Refraction Parallax 2 Altitude. Chronometer. Means Index Corr., &c. a Refraction Parallax 2 Altitude. Chronometer. Q 1 II 63 15 .30 45 63 15 30 45 ft. m. H. 2 7 23. 8 2.5 8 40.6 10 11.0 10 50. 4 11 30. O / /' 63 45 30 15 03 45 30 15 h. in. 8. 10 36 55. 8 37 34.8 38 15.0 39 43. 40 23. 41 3.8 63 30 0.0 + 2 37.5 2 9 26.2 f,:i 30 0.0 + 2 37/5 10 38 59. 2 o Ther. 65. 5 in. Bar. 29.70 O i ii = 71 19 5. 3 ll. M. 8. . 7 45 4.3 - + 6 9.5 O ' ft 71 24 10. 1 7l. TO. 8. . 4 14 38.5 4- 6 8. 9 63 32 37.5 1 29.8 + 7.2 <>:: :w 37.5 1 28.3 + 7.2 * Polar distance of Local Apparent T Equation of Time Local Mean Time Time by Chronon Chronometer fust These observatio object . . me . . . Polar distance of Local Apparent T Ki|ii:ilion of Time Local Mean Time Time l>,y ('hronom Chronometer last These observatio iibjcct me 7 51 13 8 4 20 47.4 eter . . . of Local M. T. . 2 9 26.2 eter . . 10 38 59.2 of Local M. T. . 6 18 12.4 . 6 18 11.8 ns were made before noon. us were made after noon. OBSERVATION'S OF THE ECLIPSE OF AUGUST 7, 1869. 75 SCHEDULE A Continued. SUN .... JULY 29. SUN JULY 30. Index Corr. E Index Corr., &c. On Arc = u. Oil' Arc = u l . Index Corr. E Index Corr., &c. On Arc = u. ".Off Arc = 6i l . HMM i it 29 5 10 15 Of" 4 25 50 26 i n O t ft + 2 26. 6 + 10.5 + 2 24.2 + 13.8 + 2 37. 1 + 2 38. Means Index Corr., &c. il Befractiou Parallax 2 Altitude. Chronometer. Means Index Corr., &c. Q Refraction Parallax 2 Altitude. Chronometer. O ' " 61 45 30 15 61 45 30 15 h. m. s. 10 42 16.5 42 57. 43 37. 45 3.0 45 44. 46 24.2 o ' " 75 45 76 75 30 75 45 A. m. 8. 2 41 46.5 42 25. 43 56.5 44 37.2 61 30 0.0 + 2 37. 1 10 44 20. 3 75 45 0. + 2 38. 2 43 11.3 c Th.-i-. 7 !. O in. Bar. 29. 63 o / ' = 71 24 13. 3 h. m. n. . 4 19 59. 8 4- 6 8.9 / /.' = 71 33 53. 9 h. m. s. 8 18 52. 1 . + 6 7.2 61 32 37. 1 1 32.0 + 7.2 75 17 38.0 1 10.9 4- 6.7 Polar distance of Local Apparent T Equation of Time Local Mean Time Time by Chronom Chrouiimeler last These obscrvatio object me Polar distance of Local Apparent T Equation of Time Local Mean Time Time by Clirononi Chronometer fast These observatio object . . me ... 4 26 8.7 . 8 24 59. 3 eter . of Local M. T. . 10 44 20. 3 eter . of Local M. T. . 2 43 11.3 . 6 18 11.6 . 6 18 12.0 ns were made after noon. is were made before noon. 76 REPORT OF PKOFESSOR HAEKNESS. SCHEDULE A Continued. SUN .... JULY 30. SUN .... JULY 30. Index t'orr. E Index Corr., &c. On Arc = u. Off An- = (A Index Corr. E Index Corr., &c. On Arc = u. Off Arc = w'. / // 29 20 20 20 C ' " 4 25 50 55 50 i a 29 10 20 15 Q 1 It 4 2<i 10 1(1 5 + 2 24. 2 + 14.4 + 2 18.4 + 10.6 4- 2 38.6 + 2 29.0 Means Index Corr., &e. H Refraction Parallax 2 Altitude. Chronometer. Means Index Corr., &c. a Befraction Parallax 2 Altitude. Chronometer. Q t II 77 45 78 15 77 45 78 15 It. m. a. 2 47 11.5 47 51.8 48 33.6 50 3.0 50 44. 9 51 25.0 O ' " 62 (il 45 30 62 61 45 30 II. III. 8. 10 40 46.5 41 27.0 42 6.9 43 35. 44 15.0 44 55.5 78 0.0 + 2 38. 6 2 49 18.3 61 45 0.0 + 2 29.0 10 42 51. c Ther. 71. i. Bar. 29. 69 ' II = 71 33 57. 6 h. m. s. . 8 24 58. 6 -f 6 7.2 O 1 II 71 38 46.7 Jl. }ll. 8. . 4 18 32. . + 6 6. 4 78 2 38. 6 1 8.2 + 6.6 61 47 29. 1 30.8 + 7.2 Polar distance of Local Apparent T Equation of Thin Local Mean Time Time by Clirouon Chronometer fast These observatii object ime . . . Polar distance of Local Apparent T Equation of Time Local Mean Time Time by Chronoir Chronometer fast These nhservatii object . . ime . . . eter . . . of Local M. T. eter . of Local M. T. . 8 31 5. 8 . 2 49 18. 3 . 4 24 38.4 . 10 42 51. . 6 18 12.5 . 6 18 12.6 us were made before noon. us were made after noon. OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 77 SCHEDULE A Continued. SUN .... JULY 30. SUN .... JULY 31. Index Corr. E Index Corr., &c. On Arc = u. Off Arc = cA Index Corr. E Index Corr., &c. On Arc = u. Off Arc = u'. / // 29 10 30 35 ' " 4 26 5 5 15 / // 29 10 15 25 O ' '/ 4 26 10 + 2 13.4 + 10.1 + 2 20.0 + 13.7 + 2 23. 5 + 2 33. 7 Mem Index Corr., &c. U Refraction Parallax 2 Altitude. Chronometer. Means Index Corr., &e. a Refraction Parallax 2 Altitude. Chronometer. O I II 60 59 45 30 CO 59 45 30 It. III. S. 10 46 7. 5 46 48.2 47 28.0 48 55. 4!) 36.5 50 15.3 O / '/ 75 . 15 30 75 15 30 /I. III. S. 2 40 33. 5 41 14.0 41 54.5 43 23. 5 44 4.3 44 44.5 59 45 0.0 + 2 23. 5 10 48 11. 8 75 15 0. + 2 33.7 2 42 39. o Ther. 79. i. Bar. 29. 61 o / // = 71 38 -19.7 /I. III. 8. 4 23 53. 5 + 664 o / // = 71 48 39.9 h. m. a. . 8 18 20. 8 . + 6 4.4 59 47 23. 5 1 34.5 + 7.3 75 17 33.7 1 10.4 + 6.8 Polar distance of Local Apparent T Equation of Time Local Mean Time Time by Cbronom Chronometer fast These olisurvutiu object . . me . . . Polar distance of Local Apparent T Equation of Time Local Mean Time Time by Chronom Chronometer fast These observatio object . . me 4 29 59.9 8 24 25 2 eter . . . of Local M. T. . 10 48 11.8 eter . . . of Local M. T. . 2 42 39.0 - 6 18 11.9 . 6 18 13.8 is were made after noon. IN were made before noon. 78 EEPOKT OF PROFESSOR HARKNESS. SCHEDULE A Continued. SUN . . . . JULY 31. SUN .... JULY 31. Index Corr. E Index Corr., &c. On Are==u. Off Arc = <j 1 . Index Corr. t E Index Con-., &c. On Arc = u. Off Arc = cj'. / // o / a / // 29 20 30 35 O / " 4 26 10 15 10 + 2 20.0 + 14.4 + 2 12.0 + 10.5 Chronometer. + 2 34.4 + 2 22.5 Means Index Corr., &c. n Refraction Parallax 2 Altitude. Chronometer. Means Index Corr., &c. a Refraction Parallax 2 Altitude. Q 1 II 78*30 45 79 78 30 45 79 7l. Ml. 8. 2 50 3. 50 44.5 51 26. 52 54. 5 53 36. 54 17.2 o / /' 62 61 45 30 62 61 45 30 li. m. s. 10 39 55. 2 40 35. 3 41 15.5 42 44.2 43 24. 5 44 3.2 78 45 0. + 2 34. 4 2 52 10. 2 61 45 0.0 + 2 22.5 10 41 59.6 o Ther. 72.5 iii. Bar. 29. 68 ' " = 71 48 45. 9 7l. III. 8. . 82751.9 . + 6 4.4 O f ft = 71 53 38. 7 /(. III. S. . 4 17 42.9 + <> 3 4 78 47 34. 4 1 6.1 + 6.6 61 47 22. r, 1 28.8 + 7.3 Polar distance of Local Apparent T Equation of Time Local Mean Time Time by Chronoui Chronometer fast These obaervatio object line . . . Polar distance of Local Apparent T Equation of Time Local Mean Time Time by Clironom Chronometer last These obsenalio object . . me eter . if Local M. T. 8 33 56 3 . 4 23 46.3 . 10 41 59.6 eter - of Local M. T. . 2 52 10.2 . 6 18 13.9 . 6 18 13.3 us were made before noon. is were made after noon. OBSERVATIONS OF THE ECLIPSE OP AUGUST 7, I8G9. 79 SCHEDULE A Continued. SUN .... JULY 31. SUN .... AUGUST 4. Index Corr. E Index Con-., &c. On Arc = u. Off Arc = u 1 . Index Corr. E Index Corr., &c. On Arc = u. Off Arc = o>. i u ' II i n 29 20 30 30 O / ii 4 26 10 15 10 + 2 12.0 + 10.0 + '.> 10.8 + 13. + 2 22. + 2 23. 8 Menus Index Corr., &c. 11 Refraction Parallax 2 Altitude. Chronometer. Means Index Corr., &c. Refraction Parallax 2 Altitude. Chronometer. Q 1 II 59 15 59 58 45 59 15 59 58 45 li. m, n. 10 47 18. 47 57. 48 37.8 50 5.5 50 46. 51 25.8 O ' II 72 15 30 72 15 30 h. m. s. 2 35 41. b 36 22.3 37 2.1 38 32. 1 39 12.7 39 53. 1 59 0. + 2 22. 10 49 21.7 72 15 0.0 + 2 23. 8 2 37 47. 3 o Ther. 81. 5 in. Bar. 29. 60 i II = 71 53 43. 2 ft. Mi. 8. . 4 25 4.7 - + 6 3.4 o Ther. 80.5 in. Bar. 29. 47 c / /' = 72 50 38. 8 h. m. s. . 8 13 44. 8 - + 5 47.4 59 2 22. 1 33.8 + 7.4 72 17 23.8 1 12.6 + 6.9 Polar distance of Local Apparrnl T Equation of Time Local Mean Time Time by Chronom Chronometer fast These obstT\ al in abject me Polar distance of < Local Apparent Ti Equation of Time Local Mean Time Time by Chrouom Chronometer fast These observatioi )bjeet me 4 31 81 8 19 32 2 eter . . . )f Local M. T. . 104921.7 ter . . . if Local M. T. . 2 37 47. 3 . 6 18 13.6 . 6 18 15. 1 is were made after noon. is were made before noon. 80 REPORT OF PROFESSOR IIARKNESS. SCHEDULE A Continued. SUN .... AUGUST 4. SUN .... AUGUST 7. Index Corr. E Index Corr., &c. On Arc = u. Off Arc = t>. Index Corr. E Index Corr., &c. On Arc = u. Off Arc = u'. i n 29 20 25 30 O ' 'I 4 26 5 25 55 26 5 i n 29 45 40 50 O 1 II 4 26 15 20 10 + 2 16.6 + 10.4 + 2 0.0 + 12.5 + 2 27.0 + 2 12.5 Means Index Corr., &c. Q Refraction Parallax 2 Altitude. Chronometer. Means Index Corr., &.c. Q Refraction Parallax 2 Altitude. Chronometer. o / " 61 60 45 30 61 60 45 30 h. m. s. 10 38 52. 39 32. 5 40 12.8 41 40.5 42 21.2 43 1.0 O 1 II 70 15 30 45 70 15 30 45 h. m. s. 2 33 28. 8 34 10.5 34 50.5 36 20. 3 37 1.4 37 42.0 60 45 0.0 + 2 27.0 10 40 56.7 70 30 0.0 + 2 12.5 2 35 35.6 o Ther. 89. 5 in. Bar. 29. 39 o / " = 73 40 5. 4 /i. in. *. . 8 11 50.0 + 5 28.4 60 47 27.0 1 28.4 + 7.3 70 32 12. 5 1 18.5 + 6.8 Polar distance of Local Apparent T Equation of Time Local Mean Time Time by Chronom Chronometer fast These observatio o / " abject . . = 72 56 3. 5 A. m. s. ime - - - - 4 10 5, r .. 6 j- r, 4r, 4 Polar distance of Local Apparent T Equation of Time Local Mean Time Time by Chronom Chronometer fast These observatio object me . . - - - - - eter - . . of Local M. T. 4 22 41. . 10 40 56.7 8 17 18.4 eter . . . of Local M. T. . 2 35 35. 6 . 6 18 15.7 . 6 18 17.2 ns were made after noon. as were made before noon. OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 81 SCHEDULE A Continued. SUN * . . . . AUGUST 7. SUN . - - - AUGUST 7. Index Corv. E Index Corr., &c. On Arc = a. Off Arc = iA Index Corr. E Index Corr., &c. On Arc = u. Off Arc = <A / n o / " / // 29 30 25 25 o ' // 4 26 5 5 + 2 0.0 + IS. 6 + 2 15.0 + 16.1 + 2 13.6 + 2 31. 1 Meana Index Corr., &c. It Refraction Parallax 2 Altitude. Chronometer. Means Index Corr., &c. Q Refraction Parallax 2 Altitude. Chronometer. o / // 74 (1 15 30 74 15 30 /I. l. 8. 2 43 42.2 44 23.2 4.') 4.4 46 34.5 47 15.4 47 56.7 O ' " 85 84 45 3(1 (1 85 84 45 30 /I. III. H. 9 30 8. 5 30 51. 5 31 33.6 33 5. 33 47. 1 34 29.4 M 15 0.0 + 2 13.6 2 45 49. 4 84 45 0.0 + 2 31. 1 9 32 19.2 o Ther. 62. 5 in. Bar. 29. 82 / /; = 73 40 12. 6 I/, in. . . 8 22 3. 1 + 5 28 4 O ' '/ = 73 44 59.4 /I. 111. S. 3 8 36.0 _j_ 5 "fi 2 74 17 13.6 1 13.3 + 6. 8 84 47 31. 1 59. 5 + 6.3 i'nlar distance of ( Local Apparent T Equation of Time Local Mean Time Time by Chrouoin Chronometer fast . The.se observatio llljeet me Polar disfaiiec ul' Local Apparent Ti Equation of Time Local Mean Time Time by Clironom Chronometer last These observatioi >hject me 8 27 31 5 3 14 22 eter . . . of Local M. T. . 2 45 49. 4 itcr . if Local M. T. . 9 32 19.2 . 18 17.9 . 6 18 17.0 is were made before noon. is were made after noon. 11* 82 REPORT OF PROFESSOR HARKNESS. SCHEDULE A Continued. SUN ' . . AUGUST 7. SUN .... AUGUST 8. Index Covr. E Index ('CUT., &<. On Are = u. Off Arc = w 1 . (Mi Arc = u. Off Arc=<A i / // c i a / // ) :in :, ; Q 1 II \ 26 5 to 10 + 2 15.0 + 15.4 Index Corr. + 2 10. 8 E + 17. 8 f 2 30.4 Index Ci.n-.. Ac. + 2 28.6 Means Index Con 1 ., &c. Q Refraetion Parallax 2 Altitude. Chronometer. 2 Altitude. Chronometer. A. m. s. 82 (I (I 9 38 32. 8 PI 45 (i 39 14. r. 30 (1 39 50. 5 82 41 28.0 PI 45 42 8.8 :!0 42 50.7 / " 91 30 45 92 91 30 45 92 A. HI. S. :: 33 33. 34 16.5 35 0.5 36 36. 5 37 20.0 38 4.2 81 15 0.0 9 40 41.9 Means 111 45 0.0 Index Corr., &c. + 2 28. 6 3 35 1-. 1 + 2 30. 4 o Ther. 69.5 i. Bar. 29.75 ' " - 73 57 50. :: A. . K. 9 12 10.9 + 5 20. 6 81 47 30.4 Ther. 74. 1 9 ' 7 - + C>.4 Bar. 29.76 U 91 47 28.6 Refraction 53. Parallax + 5. 9 Polar distance of Local Apparent T Equation of Time Local Mean Time Time by Clironom Chronometer fast These oliservatio o / /' object - 73 45 5.3 A. ?. s. me 3 16 58 7 Polar distance of object Local Apparent Time '. + 5 26.2 Local Mean Time .... Time liy Chronometer . Chronometer fast of Local M. 1> 3 22 24 9 9 17 31.5 3 35 48. 4 eter . . 9 40 41.9 of Loenl M.T. . C. 18 17.0 . 6 18 16.9 us were made after noon. These observations were made before noon. OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, JSG'J. SCHEDULE A Continued. SUN AUGUST 8. On Arc = u. Oft' Arc 29 25 30 30 Index Corr. E 2 15.0 11.4 Index Con-., &c. !+ 2 26. 4 2 Altitude. Means Index Con'., &c. > IvYIVactioll Parallax 65 45 30 15 65 45 30 15 65 30 0. + 2 26. 4 65 32 26. 4 1 23.0 + ' 7.2 4 26 5 Chronometer. It. lit. 8. 10 21 93.3 22 33. 2 23 M.5 24 43.3 25 23. 5 26 3.5 10 23 58. 6 Thcr. 7(1. in. Bar. 2'J. 64 1'oliir distance of object Local Apparent Time Equation of Time Local Mean Time . . Time by Chronometer = 74 2 42.0 h. in. y. . 4 23. 1 . + 5 18.3 4 5 41.4 10 23 58. 6 Chronometer fast of Local 31. T. . 6 18 17. 2 These observations were mudo after noon. 83 84 REPORT OF PROFESSOR HARKNESS. SCHEDULE 13. Observations for Latitude, made at the temporary United States Naval Observatory at Des Moines, Jozra, by Prof. Wm. Harkn8S, U. S. N., icith the /Sextant Mclq>ole. A- Bro. No. 0,'!7. Artificial Horizon Ha. 1, and Chronometer T. >S'. & J. I). Negus No. [NOTE. Tlic barometer employed was an aneroid belonging to Professor J. E. Eastman, and O.MS of an inch must be subtracted from all its recorded readings in order tn free them from constant errors.] SUN . . JULY 23, 1869. SUN . . ' JULY 23, 1869. Index Corr. E Art. Hor. Index Con-., &c. On Arc = u. Off Are =u'. Index Corr. E Art. Hor. Index Corr., &c. On Arc = a. Off Arc = o'. i n 28 30 30 20 O / " 4 26 20 10 i tf / /' + 2 41.6 + 29.6 -f 241.6 + 29.8 + 3 11.2 + 3 11.4 Means Index Corr., &c. H f Refraction Parallax Am Bn c ft' 9 2 Altitude. Chronometer. Means Index Corr., &c. S2 ? Refraction Parallax Am Bn 6 <t> 2 Altitude. Chronometer. O ' " 136 15 30 2(1 30 24 40 135 27 20 31 40 35 40 7(. JH. 8. 6 2 7.0 3 10.8 3 55. 3 4 58.5 5 58.2 6 56.8 ' " 135 58 10 136 30 2 U!7 7 9 10 50 A. in. . (i 13 20. 8 14 14.2 14 45.0 15 57. 5 16 59. 3 17 59.0 135 55 53. 3 + 3 11.2 6 4 31. 1 136 34 35. + 3 11.4 6 r5 32. 6 o Thcr. in. Bar. 7i. HI. s. = 12 6 10. 9 (i 1H 8.0 o Ther. 86. 5 /I. Ml 8. = 12 6 10. 9 ' = 6 18 8.0 135 59 4. 5 136 37 46. 4 22 27. 8 -f- 21. 7 3.2 24 38.4 + 13.8 21 41 6.6 + 21. 4 3.1 -i 58. :: 21 3fi *J. + 19 59 3. 21 36 27. -f 19 58 57. H ;;r, ,'.-. 41 35 24. Time of Culmination . . - Chronometer fast .... Chron. Time of Culmination . Time of Culmination . . . Chronometer fast .... Chron. Time of Culmination = 6 24 18. 9 = (i 24 18. 9 OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 85 SCHEDULE B Continued. SUN JULY 24. SUN .... JULY 25. Index Con. E Art. Hor. Index Corr., &c. On Arc = a. Off Arc = u'. Index Corr. E Art. Hor. Index Corr., &c. On Arc = a. Off Arc = u>. i a 29 5 10 10 / II 1 26 20 10 t i/ 29 25 30 30 Q 1 it \ 20 10 25 55 50 + 2 20. 8 + 29.7 + 2 16.7 + 29.6 + 2 50. 5 + 2 46. 3 Mean.-. Index Corr., Ac. a i Refraction Parallax Am Bn i * 2 Altitude. Chronometer. Means Index Corr., &c. a c Refraction Parallax Am Q Bn i 9 2 Altitude Chronometer. ' " 136 17 45 20 10 22 20 135 23 10 25 10 29 30 7l. 111. X: 6 7 51.5 8 32. 9 9. 5 10 11.:; 10 55. 3 12 7.0 Q i II 136 14 40 23 10 23 30 135 21 21 40 21 10 h. m. s. 6 15 16.2 19 5. 1 21 3. 5 22 10.6 23 11.5 20 43. 5 135 53 0.8 + 2 50. 5 6 9 47. H 135 50 51.7 -f 2 46. 3 6 21 15. 1 Ther. 86. /(. HI. H. 12 6 12.0 = 6 18 8.5 o Ther. 71. 5 in. Bar. 29. 48 h. m. s. = 12 6 12.6 = 6 18 8.9 135 55 51. 3 i::r, :,:; ::..o 22 2 4.4 + 21.7 3.2 13 14.5 + 4.0 22 3 11.0 + 22.4 3.2 1 21.9 21 49 12. + 19 46 24. 22 2 8. + 19 33 21. 41 35 36. 41 35 29. Time of Culmination Chronometer last .... Chron. Time of Culmination - Time of Culmination Chronometer fast .... Chron. Time of Culmination . = 6 24 20. 5 = 6 24 21.5 86 REPORT OF PROFExSSOR HARKNESS. SCHEDULE B Continued. SUN .... JULY 26. SUN . . . JULY 27. Index Corr. E Art. Hor. Index Corr., &c. On Arc = u. Off Arc = u'. Index Corr. E Art. Hor. Index Corr., &c. On Arc = u. (Ill Arc = u'. 29 15 28 55 50 O / If 4 26 10 40 10 / n 29 10 25 25 O ' " 4 26 26 25 50 + 2 20. + 29.5 + 2 21. 6 + 29. 4 4- 2 49. 5 4- 2 51. Means Index Corr., &c. Q f Refraction Parallax Am-, ' f, 2 Altitude. Chronometer. .Means Index Corr., &c. a Refraction I'arallax <5 2 Altitude. Chronometer. ' II 135 36 50 57 50 57 45 134 55 55 20 54 40 /i. m. s. 6 21 8. 5 22 2.8 22 40. 7 23 39.2 24 13.8 24 41.5 o ' " 134 25 10 23 50 22 40 135 24 40 24 22 40 //. HI. S. 6 29 27. 5 :;o 9.7 30 48.7 31 34.5 32 I'.'.'.i : 52.2 135 26 14. 2 4- 2 49.5 6 23 4. 4 134 53 50. + 251.0 6 31 12. Ther. 79.0 I'M. Bar. 29. 51 /I. Ml. 8. = 12 6 12.6 = 6 18 9.4 Ther. 80.3 in. Bar. 29. 46 /I. Ml. S. = 12 6 12.1 = 6 18 10. 4 135 29 3.7 134 5<; IK" 22 15 28. 2 4- 22.4 3.2 11.7 22 31 39. 5 4- 22.5 3. 2 2 54. 8 22 15 36. 4- 19 20 4. 22 29 4. 4-19 6 25. 41 35 40. 41 35 29. Time of Culmination . . . Chronometer fast - - - Chrou. Time of Culmination Time of Culmination . . . Chronometer fast . - - - Chron. Time of Culmination . = 6 24 22. = 6 24 22. 5 OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 18C9. 87 SCHEDULE B Continued. SUN . . . . JULY 28. SUN .... JULY 28. Index Corr. E Art. Hnr. Index Corr., &c. On Arc = o Off Are = u l Index Corr. E Art. Hor. Index Corr., &c. On Arc = u Off Are = u 1 / // 28 50 20 29 o / // 4 25 50 26 10 26 10 i n O ' " + 2 30.0 + 29.3 0.3 -f 2 30. + 29.3 + 0.3 + 2 59. + 2 59. 6 Means Index COIT., &.c. a f Refraction Parallax .tnl Iin 6 * 2 Altitude. Chronometer. Means Index Corr., &c. a f Refraction Parallax Am s B*o f $ 2 Altitude. Chronometer. / II 135 o no 2 r, 2 25 133 59 50 59 30 59 40 It. HI. s. 6 20 11. 21 7.5 21 50.0 22 40. 23 13.0 23 42.5 o / '/ 133 59 30 134 133 59 40 135 2 35 1 30 1 20 It. in. s. C, 25 8. 25 43.2 26 15.8 26 59.5 27 50. 5 28 29. 2 134 :J 43.3 + . 2 59. 6 22 7.3 134 30 45. 8 + 2 59. 6 6 26 44. 4 /I. lit. S. = 12 6 10.9 = 6 18 11.5 o Ther. 71. in. Bar. 29. 59 /i. HI. . = 12 6 10.9 = 6 18 11.5 134 33 42. 3 134 33 45.4 22 43 8.8 + 23.1 3.2 23.1 22 43 7. 3 + 23.1 3.2 25.5 22 43 6. + 18 52 36; 22 43 2. + 18 52 33. 41 35 42. 41 35 35. Time of Culmination . . . Chronometer Cast .... Chrnn. Time of Culmination . Time of Culmination . . . Chronometer fast .... Cliron. Time of Culmination . = 6 24 22. 4 = 6 24 22. 4 REPORT OP PROFESSOR IIARKNESS. SCHEDULE B. Continued. SUN .... JULY 29. SUN . . . . JULY 29. Index Corr. E Art, Hor. Index Corr., &c. On Arc = u. Off Arc = u'. Index Corr. E Art. Hor. Index Corr., &c. On Are = o. Off Arc = o'. i a Ct t 11 -/ // 28 40 50 40 Q i it 4 25 50 26 20 + 2 40.0 + 29.1 + 0.3 + 2 40. + 29.1 (1.3 + 3 9.4 + 3 8.8 Means Index Corr., &c. f Refraction Parallax Am Bn f, fi <i> 2 Altitude. Chronometer. Means Index Corr., &c. a f Refraction Parallax Am B 6 2 Altitude. Chronometer. o / // 134 34 10 34 35 34 30 133 31 30 31 25 31 20 /i. m. s. 22 12. 1 22 56.7 23 30.6 24 17.0 24 49.2 25 19.5 O in l:i:i 31 10 :ui n 29 50 134 32 20 31 40 31 //. HI. S. 26 46. 27 35.0 27 59.0 28 44.0 29 24. 29 54. 6 Kit 2 55.0 + ' 3 9.4 6 23 50. 8 134 1 0. + 3 8.8 6 28 23. 8 7i. m. s. = 12 fi 9.2 = C 18 12.0 o Ther. 74.5 in. Mar. 29.66 /i. m. s. = 12 9.2 = 6 18 12.0 134 6 4.4 134 4 8.8 22 56 57. 8 + 23.0 3.3 0.1 22 57 55.6 + 23.0 3. 3 1 2.3 22 57 12. + 18 38 23. 22 57 13. + 18 38 20. 41 35 35. 41 35 33. Time of Culmination . Chronometer fast . . . Chron. Time of Culmination . Time of Culmination Chronometer fast Chron. Time of Culmination . = 6 24 21.2 = 6 24 21. 2 OBSERVATIONS OF THE ECLIPSE OP AUGUST 7, 1869. 89 SCHEDULE B Continued. a AQUILjE - - . JULY 29. POLARIS . . . JULY 29. Index Corr. E Art. Hor. Index Corr., &r. Coincidence of Images. Off Arc = u>. Index Corr. E Art. Hor. Index. Corr.,&c. Coincidence of Images. Off Arc = <A / // 2 25 30 25 O ' " / // / " + 2 26.7 + 23.6 + 2 2C. 7 4- 15.8 + 2 50. 3 + 2 42.5 Means Index Corr., &c. Q c Refraction Parallax Am > Alg {, 6 <t> 2 Altitude. Chronometer. Means Index Corr., &c. Q 4H Refraction p cos t 2d term # 2 Altitude. Chronometer. o / // m 40 20 47 50 49 10 49 15 49 50 50 10 li. in. ft. 5 24 20. 25 34.2 26 37.0 27 28.5 23 12.4 28 57.5 / '/ 83 3-1 111 34 35 35 40 36 10 36 45 37 20 /(. m. . 5 32 53. 5 33. 53. 34 42.5 35 35. 3 36 23. 37 15. 5 113 48 45. H + 2 50.3 H3 35 46.7 + 2 42. 5 5 35 7.1 o Ther. 59. 5 ill. Bar. 29. 70 li. m. s. Ther. 59.5 IH. Bar. 29. 70 It. m. s. 6 18 12. 1 5 23 2 2 113 51 30. 1 83 38 29. 2 33 4 12.0 + 30. 6 53. 3 41 49 14. C 1 3.0 13 25. 4 + 53.1 41 35 39. 33 3 55. + 8 31 42. Chronometer fant .... t 41 35 37. Time of Culmination . . . Chronometer fast Chrou. Time of Culmination . 6 )- 88 36' 25" 5015" = 11 12 51.9 = 6 18 12. 1 P - = 5 31 4. 12* 90 REPORT OF PROFESSOR HARKNESS. SCHEDULE B Continued. SUN .... JULY 30. SUN .... JULY 30. Index Corr. E Art. Ilor. Index Corr., &e. On Arc = w. Off Arc = u'. Index Corr. E Art Hor. Index Con-., &c. On Arc = a. Off Arc = o 1 . / // 29 10 10 15 O ' H 4 26 5 10 20 i n o ' " + 2 18.3 + 29.0 0.3 + 2 18.3 + 29.0 + 0.3 + 2 47.0 + 2 47. 6 If MM Index Corr., &c. a C Refract inn Parallax Am 7? ti a 2 Altitude. Chronometer. Means Index Corr.. iVi . Q f KY Tract ion Parallax Am o Bn s C, <5 t 2 Altitude. Chronometer. O III 134 5 10 r> 45 5 45 133 2 40 3 2 :io 7l. Ml. . 6 21 47. 3 22 18.2 22 54.0 23 24. 5 24 19.2 24 50.8 c / " 133 2 30 2 25 2 5 134 4 50 4 20 4 15 /I. Ml. S. 26 3. 5 20 32.2 20 51.2 27 21.8 27 50.8 28 7.5 133 34 8. 3 + 2 47. 6 23 15. 7 i:;:i 33 24.2 + 2 47. 6 C 27 7.8 /I. Ml. S. - 12 f. 0.9 - 6 18 12.2 o Ther. 79.6 in. Bar. 29. 65 7l. Ml. . - 12 6 6.9 : C 18 12.2 133 30 55. 3 133 Itf. 11.8 23 11 32.4 + 23.0 3.3 8. 1 23 11 54. 1 + 23. 3.3 29.7 23 11 44. + 18 23 52. 23 11 44. + 18 23 50. 41 35 36. 41 35 34. Time of Cnlmiuation . . . Curonometer fast . . Chron. Time of Culmination . Time of Culmination Chronometer fast ... Chron. Time of Cnlmiuation . = 6 24 19. 1 = 6 24 19. 1 OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 91 SCIIKW.'LK B Continued. POLARIS .11 'LY 30. SUN - - JULY 31. Index ('CUT E Art. Hc.r. Index Corr., &c. Coincidence of Images. Oft Arc u'. Index Corr. E Art. Hor. Index Corr., &c. On Arc = a. Off Arc = u'. / // 2 20 15 25 O f I/ t a 29 10 5 20 o / // 4 26 25 55 26 5 4 2 20. 4- 15.9 4- 2 24. 2 + 28. 9 0.3 4- 2 35. 9 + 2 52. 8 Means Index Corr., Ac. a 4 a Refraction p r<>;- / ad term * > Altitude. Chronometer. Means Index Con 1 ., &e. Q ? Refraction Parallax Am o Bn c t lJ l 2 Altitude. Chronometer. O ' II 83 53 20 54 10 55 56 57 10 57 55 /I. III. S. 5 55 25. 1 56 43.6 57 22.5 58 47. 2 6 46.2 2 6.5 o / " 133 35 35 25 35 35 132 33 33 10 33 10 /I. Ml. 8. 6 21 27. a 22 10.8 22 50. 5 23 25. 8 24 4. 3 24 31.8 83 55 35. 8 4- 2 35.9 5 58 31. 8 133 4 13 3 + 2 52. 8 6 23 5. 1 O Ther. 63.0 in. Bar. 29.117 o Ther. 81. 5 in. Bar. 29. 02 /I. III. S. = 12 6 3.9 = 6 18 13.6 83 58 11.7 133 7 6.1 41 59 5.8 1 1.4 23 9.0 4- 50. 6 23 26 27. + 23.2 3.4 9.1 41 35 46. , 23 26 38. 4- 18 9 3. 7l. III. 8. Chronometer fast .... 6 18 12. 9 t 4 55 40.7 6 +88 36' 25". 3 p 5014". 7 41 35 41. Time of Culmination . . . Chronometer fast .... Chroii. Time of Culmination . -^ 6 24 17. 5 92 REPORT OF PROFESSOR HARKNESS. SCHEDULE B Continued. SUN .... JULY 31. SUN .... AUGUST 2. ludex Corp. E Art. Hor. Index Corr., &c. On Arc = a. Off Arc = u'. Index Corr. E Art. Hor. Index Con-., &c. On Arc = a. Off Arc u 1 . o / // / n 29 40 30 30 ' II 4 26 25 20 30 + 2 24. 2 + 28.8 + 0.3 + 2 0.8 + 28.6 + 0.3 + a 53.3 + 2 29.7 Means Index Corr., &c. f Refraction Parallax Am Bn i 2 Altitude. Chronometer. Means Index Corr., &c. Q f Refraction Parallax ^o Bn 6 4> 2 Altitude. Chronometer. o / // 133 33 20 32 45 32 20 132 29 5 28 5 26 55 /I. HI. 8. 6 28 50. 2 29 24.0 29 53. 30 20. 5 30 54. 31 17.5 Q 1 II 132 34 40 33 35 33 131 29 10 28 50 28 15 /I. l. 8. 6 26 38. 5 27 53.2 28 40.2 29 13.8 29 38.9 30 1.5 133 25. + 2 53. 3 6 30 6. 5 132 1 15.0 + 2 29'. 7 6 28 41. 7l. . 8. = 12 6 3.9 = 6 18 13.6 o Th,T. 81. in. Bar. 29.58 It. 111. 8. = 12 5 56. 4 = 6 18 14.5 133 3 18.3 132 3 44.7 23 28 20. 8 + 23.2 3.4 2 0.1 23 58 7.7 + 23.7 3.5 1 M.2 23 26 41. + 18 8 58. 23 57 14. + 17 38 27. 41 35 39. 41 35 41. Time of Culmination . . . Chronometer fast .... Chrou. Time of Culmination . Time of Culmination Chronometer fast .... Chron. Time of Culmination . = 6 24 17. 5 = 6 24 10.9 OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 93 SCHEDULE B Continued. SUN , . . AUGUST 2. a OPHIUCHI . AUGUST 2. Index Corr. E Art. Hor. Index Corr., &e. (In Arc Oft" Arc = u'.* Index Corr. E Art. Hor. ludex Corr., &c. Coincidence of Images. Off Arc = u 1 . i it / // i / // 2 15 15 25 of" + 2 0.8 + 28.5 0.3 + 2 18.3 4- 25.9 4- 2 29. + 2 44.2 Means Index Corr.,.&-c. Q ^ Refraction Parallax Am a fin 6 t > Altitude. Chronometer. Means Index Corr., Ac. a f Refraction Parallax Am Sii 6 4 2 Altitude. Chronometer. o / /. 132 20 n 25 n _:; :;:> 131 19 20 17 .in 15 45 A. in. *. (i 33 10. 33 35. 34 11.5 34 4y.O 35 24. 36 1.4 o / // 122 5 50 4 40 4 50 3 30 a 50 2 30 h. m. 8. 3 a 30. 1 341. 5 4 40.2 5 44. 6 24. 6 59.5 131 51 13.3 + a ay. o 6 34 31.8 122 4 1.7 + 2 44.2 3 4 59.9 It. Hi. . = 12 5 56. 4 = 6 18 14.5 Ther. 74.0 in. Bar. 29. 61 A. m. s. = 8 41 57. 8 = 6 18 14.6 131 53 42.3 122 6 45. 9 24 3 8. 8 + 23.8 3.5 <i 12. 28 56 37. 1 + 29.9 1 15.4 23 57 17. + 17 38 24. 28 55 52. + 12 39 41. 41 35 41. 41 35 33. Time of Culmination .... Chronometer fast - . . . : Chron. Time of Culmination . - Time of Culmination . . . Chronometer fast . - Chron. Time of Culmination . = 6 24 10. 9 = 3 12.4 94 EEPORT OF PROFESSOR HARKNESS. SCHEDULE B Continued. POLARIS . - . AUGUST 2. a AQUIL* . . . AUGUST 2. Index Corr. E Art. Hor. Index Corr., &c. Means Index Corr., &c. Q ta Refraction p cos / 2d term <t> Coincidence of Images. Off Arc = <a'. Index Corr. E Art. Hor. Index Corr.,&c. Coincidence of Images. Off Arc .= u'. / // 2 25 20 15 o ' /' / // 2 25 20 15 O 1 If . + 2 20. -r 15.8 + 2 20. + 23.5 + 2 35. 8 + 2 43.5 2 Altitude. Chronometer. Means Index Corr., &c. f Refraction Parallax Am 7?n 6 " 2 Altitude. Chronometer. / II 83 30 20 31 31 40 32 45 32 30 33 30 li. m. a. 5 12 5.2 13 35.4 14 23. 8 15 13.5 16 2.0 16 48. ' 'I 113 42 45 41 20 39 20 :!? i:. 35 10 32 30 /I. HI. S. 5 25 16. 5 26 17.8 27 9.2 28 19. 1 29 . 8. 3 30 6.8 83 31 57.5 + 2 35. 8 5 14 49.0 113 38 3.3 + 2 43.5 o Ther. 69.5 in. Bar. 29. 63 h. m. s. 6 18 14.7 5 27 45. 6 h 88 36' 25".9 5014".! o Ther. 69. 5 in. Bar. 29. 63 7l. Ml. 8. = 10 57 8. 3 = 6 18 14.6 83 34 33. 3 113 40 46.8 41 47 16.6 1 1.0 11 43.0 + 53.4 33 9 36. 6 + 35.7 (i 5:i. 7 + 0.7 41 35 26. 33 3 19. + 8 31 42. Chronometer fast .... 1 6 . . . - 9 41 35 1. Time of Culmination . . . Chronometer fast .... Chron. Time of Culmination . = 5 15 22. 9 OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1809. 95 SCHEDULE B Continued. a SAGITTARII . . AUGUST 4. Index Coir. E Art. Hnr. Index Corr., &r. Coincidence of Images. Off Arc = a'. / a 2 10 20 10 > II + 2 13.3 + 0.8 + 2 20. 1 Means Index C'orr.. Ac. a f Refraction Parallax -^"'o Bit? : , 3 <t> 2 Altitude. Chronometer. O ' II 43 40 35 40 33 50 33 30 30 29 //. HI. 8. 4 29 34. 5 30 43. 31 43.5 32 39. 33 35.0 34 16.2 43 33 40. + 2 20. 1 o Tlier. 77. U h>. liar. 29. 46 /I. III. 8. - 9 52 11.0 : fi 18 15.6 43 36 0. 1 r,s 1-2 o.o + 2 12.8 11 ;i. 9 + 0.4 68 3 3. - 20 27 15. 41 35 48. Time of Culmination Chronometer fast .... Chron. Time of Culmination . = 4 10 26. 6 96 REPORT OF PROFESSOR HARKNESS. SCHEDULE C. Observations for Time, made at the United States Naval Observatory, Wxxhinf/ton, with the East Transit Instrument, by Professor M. Yarnall, U. 8. N. [NOTE. The seoouds were marked on the chronograph sheet by the Kcssels clock, but the beginning of the minutes was taken from the face of a counting clock, which ran quite irregularly. This accounts for tin 1 discrepancy between the hourly rates and the absolute errors on the different days.] , Object. Seconds of transits. a o .ti s* Date. si ,a tg to i) ZZ Almanac R.Asccnsion. il g-o V. a I. II. III. IV. VI. VII. VIII IX. X. XI. Mean. 'c& 5JS K o O~ 1869. 8. 8. s. R. s. s. 8. 8. s. s. 8. in. s. s. h. m. s. s. July 26 1 14 16 1 17 6 07 q .,,, <i w t 11 6 V> 6 13 44 46 4 7 30.24 + 0.48 11 7 8.16 22. 56 2 /? Leouis . 29.231.3 32.5 42.5 43.5 44.7 15.9 47.0 57. 58.1 0.2 42 44. "t + 0.5o 11 42 22.67 22.55 3 6 Ursa? Min. . . _ . 33. 5 52. 26.5 18 57. 40 3 45.71 . 22. 45 4 a Lyrse . .35.3 37/9 39/3 51. 6 52.9 54.5 36/0 57. 3 9.7 11.0 13.7 32 54. 47 + 0. 43 18 32 32. 45 22. 45 5 e Delphini . 6. 11 8. 3 9. 4 19.0 20.2 21.4 22.6 23. 7 33.4 34.6 36.6 27 21.39 + 0. 51 20 26 59. 48 22. 42 6 li Aquarii . 143.946.247.4 57.1 58.2 59.3J 0.6 1.6 11.2 12.4 14.6 45 59. 32 + 0. 57 20 45 37.4722.42 29 7 & Ophiuchi . 35. 6 37.938.9 48.5 49.6 50.751.1) 52. 9 2.6 3.7 5.8 7 50.74 + 0. 43 16 7 30.60 20. 57 8 3 <1 *> 7 6 8 16 r > 17 6 18. 8>20. ''I 30 8 31 9 34 30 18.77 + 0. 46 16 29 58. 67 20. 56 9 K Ophiuchi . 47.7 48.8 50.051.2 52.2 1.9 3.0 5.2 51 55.00 4.66 16 51 29. 79 20. 55 10 t- I'rsie Mill. 3.8 18/4 26/8 37.8 45.2 54.8 4.2 11.3 22.5 30. 8 46. 4 59 54. 73 1.85 20. 55 11 7 Aqnibi' 9.1 11.2 12.3 21.9 23.0 24.325.5 26. 5 36. 3 37. 4139. 6 40 24.28 -f- 0. 38 19 40 4.15 20. 51 12 j3 Aquila- 0.0 2.1 3.1 12.7 13.8 15. 16. 2 17.4 26.9 28. 30. 2 49 15.04 -)- 0.40 l!i 4* 54.93 20. 51 111 / 1'i-siH Miu. . . . 57.0 57.0 56.059.0 51.0 _ . 56 56. 00 10.44 ... 20. 51 14 15 IT Caprieorni p Aqnarii . 55.8 42.3 68.1 44.5 59.2 45.7 9.1 55.3 10.3 56.4 11.6:12.8 57. 6158. 8 13.9 59.8 24.1 9.5 25.427.6 10.712.8 20 11.63 45 57.58 + 0. 50 -)- 46 20 19 51.62 20 45 37. 54 20. 51 20. 50 30 16 l'i Leonis . 28.0 30.2 31.2 41.2 42.2 43.644.i- 45. 9 55.8 56.9 59. 1 42 43. 54 + 0. 23 . 21.29 17 Polaris.8.P.18.0 6.5 5.0 55. 20. 5 . . _ . . . 49 9. 00 +22 46.21 . 21. 28 18 C Ophiuchi - 4.2 6.4 7.4 17.2 K3 19.5 20.7 21.7 31.5 32.6 34/8 30 19.48 + 0. 37 16 29 58.63 21. 22 19 a Opliiut-lii . 58.5 0.7 1.9 11.7 12.8 14.1 15. 3 16.4 26.2 27.2 29.4 29 14.02 + 0. 29 IT 29 53. 10 -21. 21 20 X Urae Min. . . 55. 5 49.0 50. 55. 50. . . . . _ . 56 51.90 14. 83 . 21. 18 21 a- Caprieorni 54.9 57/058.3 8.0 9.1 10.4 11.6 12.6 22.5 23. 6 25.8 11 10.35 + 0. 3s 20 10 49. 56 21. 17 22 TT Caprieorni 56. 6 58. 8i59. 9 10.0 11.1 12. 4 13. 7 14.8 25.0 26.2 28.4 20 12.45 + 0. 41 20 19 51. 69 21. 17 23 /; A(iuarii . 43.2 45. 3 46. 4 56.1 57. 2 58.4 V.l. 6 0.6 10.4 11.5 13.6 45 58. 39 + 0. 37 20 45 37.59 21. 17 24 C Cygni . . 27. H 30.1 31.4 42. 5 41 1. ? 45. 46. 5 47.7 58. 6 0.0 2.5 7 45.07 + 0.21 21 7 24. 12 21. 16 31 25 C Ophiuchi . 4.7 6.9 8.0 17.7 18.7 20.021.2 22. 3 32. 2 33. 2 35. 2 30 20.01 + 0.44 16 29 58. 58 21.87 26 K O])hiuchi . :!6. (i 38.2 39. 3 49.0 50. 5 1. \! .V,'. 1 53. 5 3.2 4.4 6 5 51 51.25 + 0.3S 16 51 29.76 21.87 27 < Ill-mi 1 Min. 4.4 18.6 27.1 38.2 46.1 55.0 3.4 11.7 23.5 30. 9 46.3 59 55. 02 0. 52 . 21. 86 28 a 1 HcTculi.s . 48.2 :>(). 4 51. 5 1.4 2.6 3.7 4.9 6.0 16. 17.1 19.2 9 3.73 + 0. 37 17 8 42.24 21.86 29 (! Ursa- Min. 35. 5 51. 11.532.5 49.7 . . _ _ 15 12. 04 1. 75 . -21. 85 30 a Lyra 1 , . . 51/1 52.3 53. 8 55. 5 56.9 . . 132.6 35. 9 37/3 39.0 40. 5 33 15.49 21.27 18 32 32.38 21. 84 31 TT Caprieorni 57. 59. 5 0.6 10.8 11.7 13. 14. 3 15. 4 25. 5 26.6 28.9 20 13.03 + 0.4? 20 19 51. 68 21. 82 32 f Delphini . j 5. 7 7.8 9.0 18.7 19.8 21.0J22.2 23.4 33. 34.2 36.2 27 21.00 + 0. 38 20 26 59. 57 -21.81 33 u Aquarii . 43.7 45. 9 47.0 56.7 57. 8 59.0 0.2 1.3 11.0 13.1 14.1 45 5S. 9s + 0. 44 20 45 37. 61 21. 81 Aug. 7 34 ft Oeininor. . . 18.7 21.4 !>. .- 24.3 25.7 38 22. 58 37. 78 27.22 35 C Ophiuclii . 9/8 11.9 13/0 22/9 24.0 25. 1 -.'6. 3 27.4 37.7 38.2 40.4 30 25. 11 + 0. (il 16 29 :,-. 66 27.17 36 K Ophiuchi . 41.2 43. 3 44. 4 54.2 55. 2 56. 5 87. 6 58. 8 8.4 9.6 11.7 52 56. 45 + 0. 53 16 51 29. -1 -27. 17 37 r Ursa 1 . Min. 7.7 83. 6(31.9 42.8 49. 9 59. 7 7.9 15. 9 27. 5 34. 5 50. 6 59 59. 27 0. 44 . 27. 17 38 a' Hereulis . 53. 3 55. 5 : 56. 7 6.5 7.6 8.9 10. 1 11.3 21.0 22.2 24. 3 9 8.85 + 0. 51 17 8 42. 19 27.17 . 39 c! I rs;e Mill. 2. Oi:i7. 5 55. 38. 5 56. 17.037.0 55. 5 37. 5 56. 5 29.0 15 16.50 2. 54 . 27.17 40 K AquilfP 4.3 6.4 7.5 17.4 18.3 19.620.8 21.8 31.7 32. 6 34. 5 30 19.54 + 0.60 19 29 52. 98 27. 16 41 y Aquihe 5.3 7.6 8.7 28. 5 29.5 30. ,-::>. o 33. 2 42.9 43.9 46.0 40 30.71! + 0. 53 19 40 4. 13 27.16 42 e Delphini . 10.913.4 14.1 23.8 24.8 26. 2i27. 5 28. 5 38.2 39.3 41.4 27 26. 16 + 0. 53 20 26 59. 54 27.15 43 ft Aquarii . 48.750.952.0 1.9 2.8 4.0 5.1 6.2 16.0 17.1 19.1 46 3.98 + 0.61 20 45 37.44 22. 15 T* 4-r* Clock Hourly 10. Good observation. Date. correction vat,-.' n. c. 18. Good observation, through thick haze. 27. Very nnsteadv. 29. Very unsteady. 1809. Aug. 7. Stars unsteady throughout the night. h. R. s. s. s. s. r. July 20 16.5 22.48 + 0.014 + 0.48 - 0.17 + 0.06 July 26, 12h. Image west, 0.24. Clamp east . 29 18. C 20.53 + 0.014 + 0.51 - 0.23 0.09 July 26, 61). Image west, 0.25. Clamp east. 30 18. 3 21.20 -f 0.014 . . 0.09 Image west, 0.45. Clamp west. 11.2 - . . + 0.35 0.10 30,211i. linage west, 0.36. Clamp west. 16.4 . -j- 0.43 0.20 . Image west, 0.15. Clamp east. 31 18. 6 21.84 + 0.015 + 0.35 0.18 + 0.06 31, Imago west, 0.10. Clamp east. Aug. 7 17.3 27.17 + 0.005 + 0.50 0. 25 + 0.07 Ang. 7, 21h. Image west, 0.18. Clamp east. Image west, 0.41. Clamp west. REPORT PROFESSOR JOHN R. EASTMAN, U. S. N. 13* REPORT OF PROFESSOR J. R, EASTMAN, U. S. N. UNITED STATES NAVAL OBSERVATORY, Wa-sMn-gtoii, D. C., September 28, 1869. Sin: In obedience to an order from the honorable Secretary of the Navy, dated June 14, 1869, I have the honor to submit to you the following report of my observations of the solar eclipse of August 7, 1809, at Des Moines, Iowa. In company with the other members of the party, I left Washington on the 5th and reached Des Moines on the 10th of July. A site for the temporary observatory was immediately selected in the northern portion of the city, on the north side of Short street, between Second and Third streets; but, owing to the extremely bad weather, tiro building, together with the small inclosure for the protection of the meteorological instruments, was not completed until July 20. The following is a list of the instruments taken from Washington: One telescope and stand one actinometer ; one photometer ; one barometer (aneroid) with attached thermometer; one dry- bulb thermometer; one wet-bulb thermometer; one solar thermometer ; maximum and minimum thermometers; and three mean-time box chronometers, (T. S. & J. D. Negus, Nos. 1275, 1.'500, and 1319.) The telescope and chronometers were taken from the Observatory, but the other instruments were my private property. DESCRIPTION Ot The Telexe<>i>c. The focal length of this instrument is IS. 5 inches, and the diameter of the object-glass is 3.5 inches. The. celestial eye-piece has a power of 50, and is fitted with three colored shades of red, green, and neu- tral-tinted glass. The stand and the equatorial mounting were made by H. G. Fit/, of New York, and, though working very badly, fulfilled all the conditions required on the day of the eclipse. The Actinometer. This instru- ment is in many respects similar to the one used by the Rev. G. C. Hodg- kinson in the Alps in 1866,' and was made by Messrs. F. W. and It. King, of Baltimore, from sketches and specifications which I furnished for their guidance. It consists of a ther- mometer with a spherical bulb 1.75 inch in diameter and a tube 12 inches long. At a distance of 9.25 inches from the bulb the tube abruptly ex- pands to a diameter of 0.5 inch for a distance of 1.6 inch, and terminates in a spheroidal chamber 0.8 inch in diameter, from which the air is only partially exhausted. The interior diameter of the small tube is about 0.06 inch. INSTRUMENTS. The bulb is filled with alcohol colored with aniline 100 REPORT OF PROFESSOR EASTMAN. blue, and the different portions of the instrument are so adjusted that at a temperature of about 40 Fah r. the top of the column is very near the bottom of the scale attached to the tube. An ivory scale, 10 inches long and 0.9 inch wide, graduated in millimeters, is attached to the tube, its lower end being one inch from the bulb. Below the end of the scale the tube passes through a cork bung, perforated and split to receive it, by which the actinometer is attached to the brass shading-tube when in use. In order to avoid the usual difficulties in shading the actinometer, a plain brass tube, 14.1i.> inches long and 2.4 inches in diameter, open at both ends and blackened on' the inside, was adopted, as affording the best facilities for passing the bulb from the direct rays of the sun into the shade, and still presenting no additional obstruction to radiation. In the central section of this tube it is pierced with a circular hole 1.8 inch in diameter, from which spiings a Hanged shoulder which receives and holds firmly the perforated cork on the actinometer tube, while the bulb of the ac.ti- nometer projects so far into the tube that the sun can shine completely round it. Two brass caps with plain plate-glass fitted into the ends are made to screw into the ends of the brass tube, in order to permit the free passage of the sun's rays, and at the same time prevent t In- action of currents of air. At 90 from the center of the aperture for the actinometer bulb is a screw to connect the brass tube with a socket, and a strong wood screw, (Fig. 1, a,) by which the tube is attached to a stall' or post while in use. In using this instrument, the actinometer is attached, by means of the perforated cork, to tin- brass tube, which is then so adjusted that the sun's rays fall directly on the bulb until a sufficient quantity of liquid is driven into the upper chamber; when the chamber is held lower than the bulb, the column is broken and allowed to fall to the temperature at which the instrument is to be worked. The bulb of the instrument is again exposed to the sun, and after an interval of ten seconds the height of the column is noted on the scale and recorded as the first reading. At the end of the adopted period of exposure the height is again read and recorded as the second reading in the*H, and the tube is turned away until the bulb is perfectly shaded. After the bulb has been in the shade ten seconds the height of the column is noted and recorded as the lirsl reading, and, after the same interval as before, the height is again read and recorded as the second reading in the slitulc. In the same manner the number of observations may be increased at pleasure. When the working column reaches the widened tube, more liquid may be expelled, and the observations continued as before; or, if the fall in the shade is greater than the rise in the sun, the column may be expanded until it reaches the widened tube, when, if it is not broken and is allowed to contract, enough liquid may be withdrawn to maintain the column at a proper working height. The temperature of the liquid is de- termined from a table derived from com- parison with a stand- ard thermometer to ascertain the tem- perature of the col- umn when it reaches the following points, viz: on the scale, the junction of the small and widened tubes, and the vari- ous divisions of the scale for the widened t ube. The Photometer. This instrument was devised for the pur- 1869. 101 pose of measuring the relative amount of diffused light in the atmosphere at different periods in the progress of the, eclipse, and was constructed from my own designs. It consists of one main tube of brass 10.2 inches long and 2,5 inches in diameter, intersected, at 1.8 inch from the bottom and at an angle of 30, by a small brass tube 8.0 inches long and 1.1 inch in diameter; a brass plate with a flange in the center which screws into the bottom of the main tube, and an apparatus for regulating the area of the aperture admitting the light, which tits by a thin flange into the upper end of the main tube. This apparatus (Fig. 2, <i) is inclosed between two brass [dates pierced by a hole of nearly the diameter of the main tube, and consists of two thin brass plates, each pierced by an aperture 1.46 inch square to admit the light, sliding on each other, by means of a double rack and pinion move- ment, in opposite directions. The reduction of the aperture admitting the light is measured by the revolutions of a gradu- ated disk 1.5 inch in diameter, attached to the pinion shaft and adjustable by means of a binding screw. Upon the plate at the bottom of the main tube was fastened a disk of black paper, (Fig. 2, 6,) upon which was painted a small live-pointed star, the points and center of which were white; a black circle or ring was drawn through the bases of the points, and a small black dot made in the center of the ring. In using this instrument, it is first lixed witti the main tube in a vertical position, and a thin plate of ground glass is placed over the aperture admitting light. The eye is then placed at the end of the small tube, lilting close enough lo shut out all light, and the aperture is gradually dimin- ished, by turning the head of the pinion shaft, until the "ring" in the star suddenly disappears. The observer then reads and records the revolutions of the graduated pinion head. Five readings are sullicient for a good observation. The pinion head is divided into 100 equal parts, and, as one revolution effects a change of 0.83 1 inch in the length of the side of the aperture, one division will represent a change of 0.1108 inch. Aneroid Bannm-tcr. This instrument, made by J. T. Large, is graduated to 0.02 inch, with a range of scale from 27.70 to .'51. .'JO inches, and is provided with an attached thermometer. Its errors were determined by comparison with the observatory standard, before and after the trip to Iowa, and by comparison on the day of the eclipse with an instrument owned by Mr. A. McConuell, who determined the errors of his barometer before and after the trip by comparison with the standard at the Dearborn Observatory, Chicago. Thermomclcrx. The dry, wet-bulb, and solar thermometers were made by James Green, and, upon careful comparison with the observatory standard, no scale errors could be detected. The solar thermometer has a blackened bulb, and is inclosed in au exhausted glass tube. The maximum and minimum thermometers were made by F. W. & E. King. They are mounted side by side on the same plate, and by comparison the errors were ascertained to be less than the probable error of a single reading. The Chronometers were of the common style, made by T. S. & J. I). Negus for the use of the navy, and were selected for this service on account of the steady rates which they had maintained for several months. The meteorological instruments were placed in a small inclosure, sixteen feet square, about seven yards southeast from the temporary observatory. The barometer and the dry and wet bulb and maximum and minimum thermometers were placed in a box 18 inches long, 12 inches wide, and 15 inches high, made on the east, south, and west sides of two thicknesses of louver or blind-work, with a space of 0".25 between them, and on the north side of one thickness. The top of the box was covered with thin strips of deal 2".5 wide, at intervals of 0".75. Over these crevices were placed strips of deal 2".5 wide raised 0".25 above the lower layer. A roof, projecting 0" over the south side, was placed over the box, sloping to the south, the southern edge of the box being 1".5 below the roof. This construction permitted free circulation of air, but prevented the undue influence of the sun, radiation, and currents of air. The box was securely attached to two posts nrmly driven into the ground in the northern part 102 KEPOKT OF PROFESSOR EASTMAN. of the iuclosure. Across the bottom of the box, which was 3'.5 iibovc tlio grass, were nailed narrow strips of deal to protect the instruments from disturbance from below. The three thermometers were suspended from the top of the box, near the central line, and the barometer was placed on the lattices at the bottom. From information received from Colonel J. W. Otley, engineer of the Des Moiiies Valley railroad, and from the triangulatiou of Professor -Hark- ness, I find that the barometer was 833.5 feet above the level of the sea. The solar thermometer was suspended in wooden crutches 4" above the grass and 0' south of the thermometer box. The actinometer, when in use, was attached to a post near the northeast corner of the inclostire, and the photometer was placed on a stand directly south of the actinometer. METEOROLOGICAL OBSERVATIONS. Before the completion of the observatory a daily record of the weather was made, from which the following extracts are taken, showing the character of the weather during- that period: July 10. Afternoon nearly clear; wind northwest. Evening hazy, with wind southwest. July 11. Temperature and moisture increasing-. Many cirro-cumulus clouds. Hazy in the evening. July 12. Heavy shower, with lightning and thunder, in the morning. Almost constant light- ning during the night, with considerable rain. July 13. Heavy thunder-shower in the morning, and a very heavy one in the evening. July 14. Rain in the morning; cooler in the afternoon, and clear at sunset. July 15. From daylight until W'SO 111 a. in. a severe storm prevailed, and from 7 h until 9 h the thunder was one continuous peal. Slight showers at intervals during the afternoon and evening. Wind west and northwest. July 16. A very severe storm came on at 7' 1 a. m., and lasted lour hours. For more than two hours there was a continuous peal of thunder. Clear at 4 h p. in. July 17. A heavy northeast storm during the morning. Clear at 7 h 30'" p. in. July 18. A fair day; clear most of the time. July 19. Thunder-storm in the morning; clear at 4 h 31) m p. m. July 20. A fair day. Wind north. July 21. A clear day. Wind north-northwest. July 22. Light haze during the day. July 23. Hazy and quite warm during the day. On July 22 and 23 the instruments were unpacked and mounted, and on July 24 the obscrva. tions with the barometer and thermometers were commenced and continued every day until August 9 at 3 h p. in. Having no one but Mrs. Eastman to assist me, I was unable to make so extensive a. series of observations as I desired, for I was obliged to devote a portion of my time to the use of the actinome- ter and photometer, and a large, portion of Mrs. Eastman's time Was occupied in practice with these instruments, and in recording the observations which 1 made with them. The original plan was to make the observations every hour during the day, but occasionally it was impossible to have an observer at hand when I was necessarily absent for my meals; and there were many breaks in the series on that account. I am greatly indebted to Messrs A. E. Le Merle and E. J. Ward for voluntary assistance on several occasions when the observations would otherwise have been lost. On the 28th of July I commenced the observations at 7 1 ' a. m., and continued them hourly until 7' 1 p. m. on the 29th, but, finding this too exhaustive labor, I was forced to abandon the observations during the night, though I was very anxious to determine the march of the temperature and atmospheric pressure during the entire day and night. On the morning of the 29th I commenced the observations with the actinometer and photome- ter at sunrise, and continued them as often as practicable until sunset. The observations were fre- quently interrupted by patches of light haze, and I realized, more fully than ever before, the fact that perfectly clear days are extremely rare in August, even in the unusually pure air of Iowa. Another series of observations with the actiiioineter was made on August 4, and, though appa- OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 103 rently a clear day, the observations gave evidences of the presence of light haze before the snn, which, on careful examination, could be detected by the eye. The weather from July 24 to August 5 was generally clear and pleasant, with but little rain, which fell in showers of short duration. On the 5th of August the wind had swung around into the fjist, and the sky was overcast with cumulo-stratus clouds. A few drops of rain fell at 8 h a. m. and again in the afternoon. On the morning of the Gth the wind was blowing hard from the northeast, and the clouds were much more dense than on the 5th. At II 1 ' 30 111 a. m. a misty, drizzly rain commenced, and lasted until I 1 ' .'>0"> ]>. m., when the temperature began to rise, and there was a change from gray to black in the color of the clouds. The clouds grew darker and more dense until dark, when it seemed that a heavy northeast storm was unavoidable. During the evening, telegrams from stations east and west of Des Moines reported the sky "perfectly clear" at Chicago and Davenport, and "clear" at Omaha, while the indications of a storm seemed to increase at Des Moines until ll h p. m. The meteorological observations for each day, save August 7. will be found in Tables I to VII, inclusive. All the corrections, except for elevation, have been applied to the readings of the baro- meter ; and the readings from the thermometer scales require no correction. The results of the observations with the actinometer on July 29 and August 4, and with the photometer on July 29, are given in Tables VIII and IX. OPERATIONS ON SATURDAY, AUGUST 7. At sunrise the whole sky was completely overcast, though the clouds were in many places less dense than on the previous evening, and there were some signs of approaching fair weather. At this time the wind was very changeable, and blew from all points between north -northeast and southeast, increasing in force as it swung around to the southeast, and decreasing as it moved back to the north-northeast. At 7 h 30 m the wind became steady from the southeast, and blew a stiff' breeze, while the moisture in the atmosphere became perceptibly less than on the Gth. At S 1 ' the clouds began to break up into detached masses and rapidly disappear. At 10 h the force of the wind had abated considerably, and small masses of fleecy clouds and patches of light haze were all that remained of the ominous gloom of the early morning. The observations with the barometer and thermometer were commenced at 9 1 ' a. m., but, owing to the prevalence of drifting clouds, the acti- nometer and photometer were not used until II 1 ' a. m.; and even then several attempted observations between ll h and noon were interrupted and spoiled by clouds and haze. About noon the clouds increased rapidly for a short time, but soon began to disappear again, and at l h 15'" only a light haze remained to dim the brilliancy of the sun. At l h 30 m a few cumulus clouds were seen in the west, but they soon disappeared, and the only clouds seen during the remainder of the afternoon were a few light cirri, which seemed to be collected in the vicinity of the sun. The haze remained during the afternoon, and, though at several times it almost disappeared in the immediate vicinity of the sun, it was generally a serious obstacle to the satisfactory use of the actiuomcter and photometer. I intended to make a series of observations with all the instruments every half hour during the afternoon until the time of first contact, and then as often as possible until after the last contact. The first part of the plan was accomplished, but the several readjust, ments of the actinometer column, which were required by the decrease of the direct solar heat, occupied more time than I anticipated, and diminished the number of observations that I had thought it possible to make. IJesides using the various meteorological instruments, I decided to observe the "first contact," the beginning and end of " totality," the various phenomena of totality, and the " last contact" of the eclipse. After some conference with Professor llarkness, I had decided that, as the success of the spec- troscopic observations depended greatly upon the rapidity and steadiness with which the instrument was directed to the different points to be examined, I would, by means of the finder, direct the tele- scope, to which he had attached his spectroscope, to the most prominent objects and, at the same time, note the general phenomena of the totality. During the afternoon Mrs. Eastinan recorded my observations with the actinometer, the baro- meter, and the thermometers, and made the observations with the photometer, except during totality, 104 REPORT OF PROFESSOR EASTMAN. when, \vitli the assistance of Mr. D. P. Marryatt, jr., of Chicago University, who kindly volunteered his services, she made all the observations that were obtained with the above instruments. At two minutes before the computed time of first contact I took my position at the 3".5 tele- scope, the aperture of which had been reduced to l".7o, and carefully examined the sun's disk, upon which were seen very distinctly three groups of small spots and two large single spots. The c\r- piece used had a power of 50, and I obtained a very clear and well-defined image. The first apparent contact of the limbs of the sun and moon was observed on the north \\csi limb of the sun at 9 b 59 m 22 S .5 by chronometer, (Negus 1300.) This was several seconds later than the computed time, and from the observed motion of the moon's limb for the next five seconds I concluded that the actual contact occurred from four to five seconds before it was detected by the. eye. The edge of the moon, as projected on the sun's disk, was as sharp and well defined as the limb of the sun. Soon after returning to the use of the meteorological instruments the actiuometer and photo- meter exhibited a decided change in the amount of heat and light, but the varying amount of ha/.e operated unfavorably upon the attempt to ascertain precisely when the instruments would have detected the change. The decrease of heat and light progressed steadily until about 4 h 20'", when an unusual collec- tion of cirri and haze shut off a large portion of the light and heat of the sun, as will be seen by reference to the observations or to the curves on Plate VIII, for nearly ten minutes. As the eclipse progressed the wind gradually decreased and blew in little pnffs, the sun's light became visibly diminished, the distant landscape assumed a different hue, and a slight moist chilli- ness seemed to pervade the air. 'The actiuometer now needed careful attention and frequent adjustment, and the photometer showed that the light was rapidly diminishing. The landscape on the eastern bank of the Des Moines River had a greenish-yellow hue, as if seen through tinted glass, and the shadows of the trees had almost disappeared. The countenances of the observers had a sickly, ghastly appearance, and the peculiar chilliness had increased until it was A T ery uncomfortable. What sunlight there was left at 4 h -40 m seemed, as it fell upon the observatory and the adjacent grounds, like the feeble reflected light from a large conflagration at night. The totality was now near, and, after adjusting the actinometer for the observation during totality, I went into the observatory to prepare for the observations. The object-glass of the finder which I used for the observations during the total phase was 0.08 inch in diameter, and the eye-piece had a power of 10. The definition of the sun's image as exam ined before the eclipse was very good. The neutral-tinted glass for the protection of the eye before totality was in a brass cap fitting loosely over the object-glass. At two minutes before the computed time for the beginning of the total phase I carefully exam- ined the portion of the sun then visible, and also that portion of the moon that was well defined, and found the edges of both sharp, with no indentations or irregularities of any kind, and none appeared until the instant of totality, when the cusps of the crescent-like band of light suddenly became obtuse, and, retreating towards the central line of the crescent with the velocity of lightning, the last ray of light disappeared at II 1 ' 1 36 8 .8, by Negus 1300. The moment the cusps of the sun's light became obtuse I removed the glass shade, so that the last view of the light was unobstructed and not bright enough to be disagreeable. The total obscuration was coincident with the appearance of the corona and protuberances and with the rush of a peculiar, almost tangible darkness. The corona (Figs. 1 and 2, Plate IX) appeared as if a screen had been suddenly withdrawn to present it as a background for the better exhibition of the black body of the moon and the colored prominences. I was considerably disappointed with the appearance of the color and brilliancy as well as with the extreme contour of the corona. Most observers have described the color as " pure" or "clear" white and the light as very brilliant, while, nearly all the published sketches represent the contour as nearly circular and regular and the coronal rays as radial and equally distributed about the body of the sun. The color of the corona, as I observed it both with the telescope and without, was a silvery white, slightly modified in the outer portions by an extremely faint tinge of greenish-violet, and ] OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 105 could not detect the least change in the color or in the position of the rays during totality. The light of the corona was not brilliant perhaps from the effect of haze but appeared more like the pale light from the train of a meteor than like anything else that I could recall at the time. The corona seemed to be composed of two portions, both visible to the naked eye, in which with the small instrument which I used, I was unable to trace any similarity of structure. The portion nearest the sun was about 1' high, forming nearly a continuous band about the sun, and appeared to be a mass of nebulous light, resembling in structure the most brilliant, irre- solvable portions of the milky way. Its color was silvery white and, like its density, appeared the same throughout its whole extent. The outer portion consisted of rays of light arranged in two different ways. In five places they were arranged into groups resembling star points composed of slightly convergent and radial rays, but elsewhere were disposed as radial lines. The color of the bases of the star points and of the radial lines was the same as that of the inner portion, while the outer portion of the points had a very faint greenish-violet tint. The radial lines were the most prominent. Four of the star points project farther from the sun than the ordinary radial lines, and give the contour of the corona the form of a trapezoid. Between the protuberances JSTos. 4 and 5 scarcely any corona was observed. As the sunlight disappeared the protuberances seemed to be thrust out from the body of the sun, and their maximum size and their color during totality is represented in Figs. 1 and 2, Plate IX. I immediately directed the spectroscope to the prominence marked "3," Fig. 3, and aftenvards o those marked "5" and " 1." Then I directed it to the points in the corona marked "CV'and "C 2 ," but no spectra were obtained until the slit was directed o that portion of the largest star point marked "C 3 ." Thinking that the end of totality was near, I took my eye away from the finder, and, seeing by the chronometer that there was yet consider- able time before the reap- pearance of the sun, I looked carefully at the co ona, and at the light as it appeared to come from a peculiar twilight in the southwest for about fifteen seconds, when I took up the beat of the chronometer in order to note the time of the end of the total phase. Pro- fessor Harkness at this moment proposed to ex- amine with the spectro- scope the large prominence that was so plainly visible on the sun's western limb. The instrument was instantly turned to this prominence, which proved to be No. 1, (previously examined,) but it had increased nearly fifty per cent, since the first examination. In order to vary the observation, the instrument was directed to the lowest point of the prominence. 14* 106 REPORT OF PROFESSOR EASTMAN. Upon the completion of this observation the instrument was directed to No. 7, and while in this position the limb of the sun appeared. The protuberance marked "1" was the largest of the series, and was the one which most attracted the attention of naked-eye observers. The color of this protuberance, like all the others, was a bright carmine, a dark shade near the base changing to a bright pink, in Nos. 1, 3, and 4, near the top. A faint dark line, as shown in Fig. 3, was the only mark of any kind observed. At the time of the second examination with the spectroscope this protuberance was very brilliant near the base, but it was at this time that the line was seen on the southern portion and that the upper portion had a pinkish tinge. The color of No. 2 appeared the same, from the bottom to the top, and when first seen there was a low line of light stretching out toward the west, along the edge of the moon. On the eastern portion of this protuberance, and nearly parallel with its eastern boundary, was a dark line much heavier than the one in the first protuberance. No. 3, when first seen, was much more curved than it appears in Fig. 3. About three seconds after its first appearance it seemed to make a half turn from the left toward the right, not gaining length by the movement, when it became fixed in the position shown by the full line in Fig. 3. The dotted line represents its outline before the change. The color of the upper portion of this pro- tuberance was very much lighter than that of the lower almost a light pink. When No. 4 was first seen it had the flickering motion of an alcohol flame in a strong current of air. This motion was so violent that at times only a trace of its light was visible beyond the limb of the moon, and, thinking that it would be impossible to examine this prominence with the spectroscope. I concluded not to waste any time in the attempt while the motion continued. In about thirty seconds the motion subsided, and this protuberance became as steady as No. 1. At that time the upper portion had a pinkish tinge. The sketch in Fig. 1, Plate IX, represents the form after the movement ceased. In No. 5, and the low range of protuberances to the north of it, the same motion was observed as in No. 4, though in No. 5 it was not so violent, and had ceased when the spectroscopic examina- tion of No. 3 was finished. This motion continued for some time in the low range of protuberances after it ceased in No. 5, but, owing to the fact that my attention was confined to the examination of No. 1, I did not notice when it ceased I only saw that it was perfectly steady before the spec- troscopic observations of the corona were commenced. No. G, and the low range of protuberances to the north of it, had the same bright carmine color throughout their whole extent, but had no motion that was perceptible. Toward the end of the total phase Nos. 6 and 7 became connected by a lower ridge of the protuberant mass, which increased in height until the end of totality. No. 7 was motionless like No. 6, and was of the same color. While examining No. 7 the sunlight, preceded about l s .5 by a lighting up of the corona, appeared exactly between Nos. and 7 not as a very attenuated crescent of light, as before the beginning of totality, but like a fleecy flame, resembling somewhat, in size and form, protuberance No. 1. This flame instantly spread along the edge of the moon, and became immediately too strong for the eye. The appearance of this light occurred at ll h 4 m 34 8 .0 by Negus 1300. I immediately made the sketches of the corona (Fig. 3) and the protuberances, (Figs. 1 and 2, Plate IX,) and wrote out my notes on the appearance of the various phenomena. Figs. 3 and 4, and Figs. 1 and 2, Plate 1 X , were sketched from the appearance of the objects in the reversing telescope. While my eye was away from the finder, just after the examination of the corona, I gave a few seconds time to the observation of the peculiar light. Owing to my position in the observatory, 1 could see only the western sky, in which the darkest portion was just outside the bounding lines of the corona. This portion of the sky had a dark slate color, changing toward the southwest to a leaden hue, but maintaining its dark slate color, with but little modification, as far east and north as I could see. This dark color prevailed in the sky west of the sun nearly down to the horizon. Near the horizon in the southwest the light resembled that of a hazy twilight, slretchiug as far south as I could see and to a point in the western horizon west 15 south. To the northward of this point there was a narrow band of grayish light on the horizon. From my point of observation it seemed that all the light we received (a very small amount) came from this southwestern twilight, though Mrs. Eastman observed a similar phenomenon in the northeast. OBSERVATIONS OP THE ECLIPSE OF AUGUST 7. 1869. 107 I coukl detect 110 resemblance between the light during totality and that of the rnoou, and can conceive of no way in which a comparison could be instituted, except by comparing the light in shadows of equal magnitude in both solar and lunar eclipses. The light more nearly resembled that from a faint twilight, about the time of the appearance of second-magnitude stars. On re- turning to the meteorological observations, I noticed that the shadows were becoming deeper, and the chilliness, so marked during totality, had nearly passed away. I found that Mrs. Eastman had made the desired observations with the actinoineter and solar thermometer, but on attempting the observations with the photometer she found the light was insufficient to render the least trace of the " star" at the base of the photometer visible. On being- assured by Mr. Marryatt that the aperture was fully open, another observation was attempted, but the "star" was not visible. A third attempt resulted in a similar failure. She then gave up the observation as hopeless, and, for the first time, looked at the corona and protuberances for a few seconds, when, thinking that her eye had become accustomed to the pecu- liar darkness, she made another attempt, with the same result as before. On the reappearance of the limb of the sun the " star" could at first be seen only as a faint, blurred image, but gradually the points of the "star," then the ring, and finally the dot, appeared by the light from the full aperture. The observations with the photometer, barometer, and thermometers were resumed at 4 h 55 m , and continued without interruption until 6 h . The work with the actinometer was recommended at 5 h 15 m , and continued, with a short inter- val at the time of the last contact of the limbs of the sun and moon, until 6 h . Tta4 A few minutes before the last contact I carefully examined the disk of the sun with the 3.5-iuch telescope, and made the sketch of the solar spots a.s seen in Fig. 4. The last contact was observed with the 3.5-inch telescope, with the aperture reduced to 1.75 inch, and occurred at 12 h l m 32 S .5 by Negus 1300. After G 1 ' the western sky became so obscured by cirrus clouds and haze that no more meteorological observations were attempted. The observations on the 7th will be found in Tables X, XI, XII, and XIII, and the results are graphically represented in Plates VI, VII, and VIII. 108 REPORT OF PROFESSOR EASTMAN. The curves for the barometer and dry and wet-bulb thermometers show but little deviation from the curve deduced from twelve days' observations. The solar thermometer shows the greatest change, and, as will be seen by reference to Table XIII, was lower eight minutes after totality than during that phase. The curves deduced from the observations with the actinometer and photometer fail, on account of the variable effect of the haze, to give that nice determination of the rate of the change in heat and light which I am confident they would have done under a clear sky. The same is true of the results of the observations Avith the solar thermometer.' Actinometer: This instrument worked better than I expected it would, though it is larger in many respects than is necessary. The scale is very easily read, and I found that under ordinary circumstances no assistant was needed in making and recording the observations. Photometer. lielying on the accuracy of the statement of former observers, that the light during a total eclipse was equal to that of the full moon, the photometer was so constructed as to show the "star" with less light than that of the full moon at an altitude of 30. I was convinced, after my observations at Des Moines, that moonlight was not a proper standard of comparison, and after my return to Washington I made a series of observations with the photometer on the decrease of light after the disappearance of the sun and when there were no clouds. I found that the appearance of the light after sunset was very nearly like that during the eclipse, and the results of the several comparisons are given below in the same terms as in Table IX. From several series of observations made in Des Homes I found the observations of Mrs. Eastman and myself so nearly identical that the differences were not appreciable in the terms given in Table IX, so that the following observations of the disappearance of the "ring" will be comparable with those made during the eclipse. The following observations were made with the "ring" until it entirely disappeared at C,, 15, and afterwards with the "star" until it was too dark to read the divisions on the pinion-head. The sun disappeared at 5 h 57 m . Time. Area. Tirue. Avon, /i. 7H. *. sq. in. li. m. s. sq. in. COO 0. 01 17 30 0.21 650 0.64 20 0.55 6 10 0.74 . 22 30 0.59 12 30 1.39 25 0.66 15 1. 93 27 ,30 0. 74 30 0. 96 32 30 1. 00 35 1. 21 At 6 h 32 m saw Saturn and Antares, and at 6,, 35 m saw second-magnitude stars. At 6 h 40 m a faint trace of the " star" could be seen ; still a trace at 6 h 45 m , at which time all the stars in the "Dipper" could be seen. No trace of the "star" at 6 h 47 m 30 s . From the above observations and from my impressions at the time of the total phase of the eclipse, I conclude that the light during the totality on August 7 was about equal to that on a clear moonless evening, at the time when third-magnitude stars can be easily seen. Chronometers. The chronometers were taken out of the gimbals in Washington and packed in cotton in a small box divided into three compartments. This box was carried in the hand, except when in the cars, and was in the care of Dr. Curtis from Washington to Des Moines. From the time they left Washington until they were packed to return I wound them every day, and, taking No. 1300 as the standard, compared them, with one exception, every day. After the observatory was completed they were replaced in their boxes, and No. 1300 placed in the photographic " dark room." Professor Harkness used 1319, and Dr. Curtis timed his photographic experiments and work by No. 1275. On returning to Washington they were repacked in cotton, as before, and car- ried by Mr. A. E. Le Merle. On July 3, before leaving Washington, No. 1275 was 5h 10 m 43 S .5, No. 1300 was 5 h 9 m 41'.5, and No. 1319 was 5 h ll m 31 s .O fast of Washington mean time. On the 31st of August, after returning from Des Moines, No. 1275 was 5 h ll m 1 8 .9, No. 1300 was 5 h 9 m 35 8 .6, and No. 1319 was 5 b 12 3 S .9 fast of Washington mean time. OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1809. 109 Time. According to the determinations of Professor Harkness, the error of No. 1319 at the time of the eclipse was C h 18 m 17 8 .2 fast of local mean time. No. 1300 was compared with No. 1319 three times on the 7th August, with the following results: It. m. .s-. It. m. .v. //. m. *. No. 1300 300 12 30 1C 8 No. 1319: 3 8 8.0 12 32 8.0 1010 8.7 Taking, from the above comparisons, the error of No. 1303 to be 2 lu 8 8 .0 less than that of No. 1319, we have No. 1300 G' 1 1C 8.C fast of local mean time. Applying this error to the times of contact, &c., which I observed, we have First contact 3 43 13.9 j 1.2 f. It. m. H. 3 43 13, Beginning of totality 4 45 28 v , _ . , n * A > -Local mean time. End ot totality 4 48 25.4 C Last contact 5 45 23.9 ) Duration of total phase 2 57.2 The meteorological observations were timed b} 1 a pocket- watch showing exact local mean time. The night of the 10th of August was so cloudy that no meteors were seen. A A^ery few were seen on the evening of the 9th, but there were no indications of an unusual display. After the eclipse most of my time was devoted to the preparation of a copy of my observations and notes, which I forwarded by express to the Observatory in Washington. "When this work was completed and the instruments packed, I left Des Moines as soon as pos- sible, and reached Washington on the 29th of August. To the citizens of Des Moines I am greatly indebted for the many social courtesies which rendered the trip to that city one to be remembered with the greatest pleasure. The thanks of the party are due the officers of the Northern Central, the Pennsylvania Central, and the Chicago, liock Island and Pacific Hallways for favors received while passing over their respective roads. Very respectfully, your obedient servant, JOHN E. EASTMAN, Professor of Mathematics United States Navy. Commodore B. F. SANDS, U. S. N., Superintendent United States Naval Observatory, Washington, D. C. 110 REPORT OF PROFESSOR EASTMAN. 8 5 M O i I S 8' 8* 18 8 CJ X X Cl Ol Oi 5* w o* c> o* ot W X l- CO X CO . X O5 O O O rH 5 SS8'i3gJgi . . : SSSSSSgi5? Ci X '^ ?0"iV-r""" -f i CC G^ X CO .XClOSOiOrH 'OOXrHWrH ...... "- '- f "/_ "/.' 51 Ci 92 SH ^ ^ ^ i ~ -^j c; -T ? -r -n- c: i / ( .ClCSOiCSOrHrH . 'OOXrHC^i-* a* 1 r a> -i o o t>. -^ . OS fli O O ^-i 1-1 1-1 = . .8* .88 - . . . < CO CO OJ -<N .8 H O - ^ a o S i o S i 5 (^ CO CO 4 O O iS -H- eo d i- CO X fi o c- - o o o o U5 o i-t o ir: x ~ s co x o w x o i^ i* c~. rt IS (N O O IS O O ' IS O iS O hS IS x i> i-* 5 r* < 'C t -i x x x r^ & t"- O O 3i tS iS IS ' S O iS iS C O . " x i^ x i-* t-* i>. 7^. x x x x c; i^ o t'. x (MX1SWOO . . -XOXOCOiO . 53 t- CO rH O CO CO ~T ( O X O <^ X I 1 * X X ! t ' X X O CC CO t~* ' iSOOXC^Tj-O t iGLSthOkSO . ssKsB^^si . .ssse& . a OiCOCOOlSiSiS 'rHiSOiSXlSCO J ^SSSP^SSS .sss^gses j l-H . ^OCOX^COiS. OOtOOrnCO J O WO^XGOrH X^-i^OCOW X i~* { t* CO t* ' ' ' 1" l^> X 1 l^ CO f* ' J USlOWOJOOMUS^OOOJCOiSiaiS S &'&?;!$$* 4 . .eo .00 . . . .ininoo oo *r so riaiaS S . . o o ift QO > " . o o .... . QC J O ^f CD i (M .00 .rf S s? * ' i -O ' 1 s? f 35 . o - ' ,d o . kS s o IS 1 "s B OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. Ill - I I 2 K H H W a 3 i-H i-t i I ( o 3 S 5 i- CO lA o t X . b o J: g lO O ** . 8 83 Iffl $ O CO O ift rt OOO (NOO500 to TT X O CO <-H 1O' O 00 ^^ ^^ T t- 00 !* to CO to . o w x x r- LO o occooomoo g in 1.0 r-' -* i- re x !> CO CO CD CO CO CO I- 00 *>. CO CO CO O O O lO O LO 1 M O 00 IN O -r t^- CO CO CO CO CO ' ' giSSS8 . *190000019 i.-; ?: o co >n m o it S c5 to cb -^ i n i~ 1 -4 Si CO 7- "J C-7 OONOOO O i 00000.0 . i gsssss . . . SSSS8S . . 1900MOOO . . O O - _ 7 1 .O i-H xO X X O ^H ^* c^ 1^- CO CO t^ CO CO CO ' * TO O C5 t^. ffl ^J O OOO OO 30O feq f:f:[:feSSg j o o m co o o o* ^ootoooo . s SSSS88S . . ssssss . . O O O 1> O I-H O O LO t- S-! ^H KSSSS2 . . . i^ ro CD to -< ^f t- (-, i>, CD CO CO -; ^0-!<NOO 8 |^ ^ t^ CO CO CO !O *! : :i :iS : : : US : : : 4 . . . o 19 o n o .... 1O Oi i^ "^ iO 19 i9tO ' .2 3 Tf J 19 tO 4 o S ' ' ' ....... J o u5 n o f, s . . . i-H o s . . . g : :i: 43 w 3 o H (S3 rH ; I 3 i m o o o SP ig tfi t^ CO LO 4 . o o o . s s o g 0019 . g g 00 S' g O CC OOO 19 o* cj to o' r^ O & 00 Ol 00 ooooooo co 10 oi u5 -r ^ O2O50C t^COOO 000<NOO S SSSSSo O O>O lOOO . O O .9 O 1C O rr gggssg 1OO1900OOOOOO n ssssss^ S -2 ^Cgj^ gg O CO CO X O A ' o! O O O X O O O - Sco . " O iC O O O CO O O - 0.000000 t~ S|''*g*^fe 88&3888SS . OOiOiOirt O 01 - O 5J1O1OO 00 ^H ^-1 . . ifl O LA b. kA iA x o o e o M co x o^ * 65 o> ^H ^H i-H i-H i-H 2^?5Sg . 19 19 10 .0 & if? CO O C: X Ot O ^ O 'T* X CN W W ^ > Of ^ O O J> ^- O5 T-< 00 O > T O t^ (>> rH A 00 . .1A .WOO . - - lA 00 lA i i O ' O ^H i . i-H i 1 i t o o >o . . d s ff . ^^ CO t*. " " ' . A , . .0000 ' . o .... co -*r o -^f GC 00 , ~ o i 'S 'S f CO 1-* 'S ' 4 o _ i ' . ' % g . . . i-H o . 10 g o CO SJCSwSwOTCOCO s 1 1 112 REPORT OF PROFESSOR EASTMAN. TABLE V. WEATHER. Day. Hour. Clouds. Portion cloudy. Wind. Day. Hour. Clouds. Portion cloudy. Wind. 3irectiou. ''orce. direction. Torce. 1869. 1869. July 24 9 Clear SW. 3 July 28 7 Clear XW. 1 10 Clear sw. 3 8 Clear N\V. 1 11 Clear SW. 3 9 Clear W. 1 Noon Clear sw. 4 10 Clear N. 2 1 Clear sw. 4 11 Clear N. 2 2 Clear sw. 4 Noon Clear N. 2 3 Clear sw. 5 1 Clear N. 2 4 Clear sw. 4 2 Clear N. 2 5 Clear sw. 3 3 Clear - N. 2 6 Clear sw. 2 4 Clear N. 2 9 Clear .0 ' sw. 1 5 C'leai- N. 2 .6 Clear N. 1 July 25 9 C. K. S. 10 NW. 1 7 Clear XW. 1 10 C. K. S. 10 NW. 1 8 Clear XW. 1 11 C. K. S. 10 NW. 2 9 Clear x\v. 1 Noon C.S. 10 NW. 2 10 Clear NW. 1 1 C.K. 10 NW. 1 11 Clear XW. 1 2 C.K. 10 NW. 2 3 C.K. 10 NW. 1 July 29 Clew- NW. 1 4 C.K. 10 NW. 1 1 Clear NW. 1 5 C. K.&N. 10 NW. 1 2 Clear NW. 1 * 3 Clear NW. 1 July 26 8 C.K. 1 NW. 2 4 S. Slight XW. 1 9 Clear xw. 3 5 S.' 1 NW. 1 10 Clear NW. 3 6 C. Slight NW. 1 11 Clear xw. 2 7 C. Slight N. 1 Noon Clear NW. 2 8 C. Slight NE. 1 1 Clear NW. 1 9 C.K. 2 N. 1 2 Clear NW. 1 10 Clear N. 1 3 Clear NW. 1 11 Clear N. 1 4 Clear NW. 1 Noon Clear X. 1 5 Clear NW. 1 1 Clear NW. 1 6 Clear NW. 1 2 Clear N. 1 7 Clear NW. 1 3 Haze" 1 N. 1 8 . Clear NW. 1 4 Haze" 1 N. 1 9 Clear NW: 1 5 Clear NW. 1 (i Haze* 1 N. 1 July 27 7 Clear NW. 1 7 C.S. 4 NW. 1 9 Clear NW. 1 10 Clear NW. 1 July 30 7 Clear II SW. 1 11 Th'kha/e 10 S. SW. 1 9 Clear sw. 1 Noon Haze C.K 10 S. 1 11 Clear sw. 1 1 C.K. 10 S. 1 Noon Clear sw. 1 2 C.K. 10 S. 1 1 Clear sw. 1 3 N. 10 sw. 1 3 Clear . sw. 1 4 N. 10 NE. 1 5 Clear sw. 1 5 N. 10 NE. 1 * In tli< west. OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1809. TABLE V. WEATHER Continued. 113 Wind. Wind. Day, Hour. Clouds. Portion cloudy. Day. Hour. Clouds. Portion cloudy. Direction. Force. Direction. Force. 1869. July 31 f, Clew SW. 1 Aug. 5 8 N. 10 E. 2 9 Clear 8W. 1 9 C. K. S. 10 E. 2 Noon Clear SW. 1 10 C. K. S. 10 E. 2 :s Cleat SW. 1 11 K.S. 9 E. 2 fl C. S. 3 SW. 1 Noon K.S. 8 E. 3 1 K. S. 8 E. 3 Aug. 1 9 C. Haze 10 SE. 1 2 K.S. 10 E. 2 3 C. Haze 8 SW. 1 3 K.S. 9 E. 2 4 K.S. 9 E. 3 Aug. y 9 C. K. 9 NW. 1 5 K.S. 9 E. 3 10 C.K. 8 N. 1 6 K.S. 10 E. 2 It C.K. f> N. 2 Noou C. K. 4 N. 1 1 C.K. S N. 1 Aug. fi 9 K.S. 10 NE. 3 9 C.K. 3 N. 1 10 K.S. 10 NE. 3 :i C.K. 3 N. 1 11 K.S. 10 NE. 3 4 C.K. 2 X. 1 Noon N. 10 NE. 3 5 C.K. 2 N. 1 1 N. 10 NE. 3 i; C.K. 1 N. 1 2 N. 10 NE. 2 3 K. 8. 10 NE. 3 Aug. 3 7 Clear SE. I 4 K. 8. 10 N. NE. 3 8 Clear SE. 1 5 K. 8. 10 N. NE. 3 9 Clear SE. 1 ii (i K.S. 10 N.NE. 3 10 Clear SE. 1 11 Noon Clear Clear SE. SE. 1 1 Aug. rf 9 10 C.K. C.K. 1 SE. 1 ' SE. 2 2 1 K. 1 SE. 1 11 Clear SE. 1 2 . K. 1 SE. 1 Noou Clear SE. 2 3 K. 1 S. 1 1 Clear SE. 2 4 K. Slight S. I 2 Clear SE. 3 5 C.K. 1 S. 1 3 Clear SE. 2 6 C.K. 1 S. 1 4 Clear SE. 2 7 K.S. 2 Calm 5 Clear SE. 2 8 C. K. S. 4 NW. 1 6 Clear SE. 1 Aug. 4 8 Clear S. 2 9 Clear S. 2 Aug. 9 9 C. 2 SE. 2 10 Clear S. 2 Noou C.K. 5 SE. 2 11 Clear S. 3 O C.K. 3 SE. 2 Noon Haze Slight S. 2 1 Haze Slight S. 2 2 Haze Very slig't SW. 1 3 Haze Very slig't SW. 2 4 Haze Slight SW. 2 5 C. Haze' 1 SW. 1 6 C. Haze* 1 SW. 1 * In the west. | 15* 114 REPORT OF PROFESSOR EASTMAN. TABLE VI. EXTREME TEMPERATURES. Day. . Maximum. Minimum. Day. Maximum. Minimum. o o o o July 24 90.5 67.0 August 1 87.5 73.5 25 75.5 57.0 2 87.5 64.0 26 83.5 62.0 3 91.0 70. 5 27 85.8 60.3 4 94.0 70.0 28 76.0 52.0 5 73.3 60.0 29 79.0 53.0 6 65.0 59.0. 30 82.0 59.0 8 80.5 56.5 31 85.5 63.5 9 88.0 65.0 RAIN. [No measurements were made before July 24.] July 25. Rain at l h a. m. Amount 27. Rain during the afternoon. Amount 0.42 inch. 0.135 inch. August 2. Light rain at l h a. m. Amount ..... - 0.085 inch. 5. A few drops of rain at 8 h a. m. and 4 h p. m. 6. A light, drizzling rain from 11" 30 m a. m. to I 1 ' 30 p. m. Total amount . . - - 0.640 inch. The following table exhibits the meaii results of the meteorological observations on July 24, 25, 26, 27, 28, 29, and August 2, 3, 4, 5, 6, and 8. On July 25 and 27 no observations were made at C h . This fact will explain the anomalous results at that hour. TABLE VII. T/mv Thermometers. -tiour. Barometer. Dry. Wet. Solar in. o o 9 29.09 73.3 67.6 112.7 10 29.08 74.3 68.1 115.6 11 29. 07 76.1 68.5 118.6 Noon 29.06 76.6 68.9 119.6 1 29.05 78.2 69.5 121.6 2 29.04 78.4 69.4 117.4 3 29.03 78.3 69.3 115.0 4 29. 035 77.1 69.0 106.1 5 29.04 76.0 68.8 95.0 6 29.05 76.2 69.5 87.5 The curves in Plates VI and VII were constructed from the data in the above table and from the observations on the 7th. OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 115 The following table shows the mean results of the observations with the actinoineter on July 29 and August 4. The solar eftect is given in millimetres, and 21 mm .7 represents 1 Fahrenheit- The exposures were 30 seconds in each case. TABLE VIII. Date and observation. Remarks. Date and observation. Remarks. It. m. mm. A. in. mm. July 29 6 40 12.6 Aug. 4 8 30 13.9 78 16. 90 12. 8 Haze. 7 35 14. 7 9 30 -14.8 8 10 16.3 10 16. 7 8 47 16.6 10 30 17.0 90 17. 3 11 16.7 9 35 16.8 11 30 15. 1 Lower cap oft' shading tube. 10 10 17.2 12 13.6 Hazy. 10 32 17. 8 1 14.0 Hazy. 11 8 20.8 1 30 14.2 Hazy. 12 5 23. 8 20 13. 9 Hazy. 1 15 25. 4 2 30 14.7 Hazy. 2 20 22.1 30 11.8 : Hazy. 32 14.2 Hazy. 3 30 12.4 : Hazy. 4 42 15. Hazy. 40 11.6 Hazy. 50 10. 8 Hazy. 4 30 8.7 Very hazy. [and haze. 5 25 10.4 5 12. 4 Sun shining through rift in cirri 60 7.9 Hazy. 5 30 3.5 Cloudy. At 6 h 30 two minutes exposure produced no effect on At ti h SO" 1 the sun was olisrurcd by cirrus clouds. the height of the column. OBSERVATIONS WITH THE PHOTOMETER. The following table shows the variations in the area of the aperture through which light is admitted to the photometer tube to render the "ring" in the "star" visible. The area is given in square inches. TABLE IX. 7(. m. Area. ft. m. Area. July 2U 4 30 1.10 July 29 I 0.02 4 45 0.26 2 .02 5 .06 3 .06 5 15 .04 3 30 .07 5 30 .04 4 30 .07 5 45 .04 5 .10 6 .04 5 30 .08 7 .06 5 45 .10 8 .03 6 (1 .09 9 .03 6 30 .11 10 .01 7 .12 11 .01 7 ir> .12 12 .004 116 REPORT OF PROFESSOR EASTMAN. TABLE X. ACTINOMETER OBSERVATIONS, AUGUST 7, 1869. d -a ' - j^ ; Sun '5 a O o 1 Hour. S* V CM O rtt O Shade First reading. Second reading. Change 1 v *S '* 2 s 3 ll 1 3 is 'i ^ ^ E- " *^2 s 3 In snn. In shade. ' .2 -5' ~. ^ EC n H & B h. m. 8. 8. mm. mm. ram. Will. mm. HI HI. mm. HI HI . 14.0 19.2 5.2 17.0 9. 5 7.5 11.9 11.7 O 10.8 11.3 3.5 13.0 8.0 - 5.0 10.6 10.4 o 21.2 29.0 7.8 11 30 ;io. o 26.3 - 3.7 10.7 224.5 67.0 10.5 10.8 27.2 33.5 6.3 35.0 28.0 - 7.0 11.2 11.0 25.5 27.5 2.0 32.5 16.0 - 6.5 10. 5 10.3 13.5 19.5 6.0 la r 13.5 - 5.0 O 87.8 95. 8 8.0 12 30 95.0 92.0 3.0 5.5 224.5 70.0 5.4 5. 4t O 91-0 88.0 - 3.0 86. 5 82.5 - 4.0 O 58. 67.5 9. 5 72. 8 69.0 - 3.8 14.1 13.8 72.8 83.8 11.0 i :;o o 30 85.5 82.0 - 3. 5 14.5 224. 5 69.0 14.2 14. Of 86.0 97.0 11.0 98.8 94.8 4.0 14.3 14.0 97.0 106.5 'J.5 130. 5 137.0 0.5 139.8 135.0 - 4.8 11.3 11.1 o 135.0 141.5 6.5 200 30 140. 5 136.5 4.0 10.4 224. 5 72.0 10.2 10.7$ 138.5 144.8 6.3 143.8 139.0 - 4.8 10.9 10.7 139.3 142.5 5.9 153.5 161.0 7.5 160.0 155.0 5. 12.2 12.0 2 30 30 o 156.5 163.5 7.0 224.5 73.0 10. 9f 164.0 161.0 - 3.0 10.0 9.8 o 164.5 171.5 7.0 o 101.0 110.0 9.0 115.5 U3.5 - 2.0 11.1 10.9 118.3 127.5 9.2 300 30 128. .0 125.8 2.2 10.6 224.5 72.0 10.4 10.4 o 130.0 137.5 . 7.5 140.2 138.0 2.2 10.2 10.0 142.5 151.0 8.5 i * Interrupted by clouds. t Cloudy. J Clear. Hazy. OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 117 TABLE X. ACTINOMETEB OBSERVATIONS, AUGUST 7, 1869 Continued. g "3 -d *S _^ Hour. iodof expoKii Sun Shade First rciiding. Second reading. Change ar eft'ect. ?! i% literature < liquid. aj ^3 Jt-H QJ ' 7" a e in solar effec 1 In sun. In shade. i i- 3 * 1 u s h. m. . . mm. mm. mm. mm. mm. mm. o mm. mm. O 139. 5 147.5 8.0 148. 5 147.0 1.5 10.5 10.3 3 30 30 O 152.0 162. 10.0 222. H 68.0 10.8 163.0 161.0 - 2.0 11.5 11.2 167.0 176.0 9.0 o 101.8 108.0 6.2 110.5 109.0 1.5 7.9 7.7 400 30 108.0 114.5 6.5 222.8 66.0 7.6 115.0 112.5 2.5 7.7 7.5 O 113.0 117.0 4.0 151.0 154.5 3.5 154.0 151.0 - 3.0 6.2 6.1 4 10 30 o 151.5 154. "> 3.0 222.5 67.0 5.2 153.0 151.0 - 2.0 4.3 4.2 o 149.4 151.0 1.6 149.0 149. 5 ,5 149.0 144. 5 4.5 4.9 * 4.8 4 20 30 143.0 143. 3 .3 222. 5 67.0 4. 3 141.5 137. 5 4.0 3. 9 _ :i. 8 136.8 136. .5 125. 5 123.5 2.0 120.0 115.0 - 5.0 2.8 2.7 4 30 30 o 112.5 110.0 2.5 222. 5 65.0 2.5 106.5 101.5 - 5.0 2.5 2.4 98.0 95.5 2.5 o 76.5 73.5 3.0 69. 5 64.5 5.0 1.8 1.8 4 35 30 59.5 56.0 3.5 222. 5 83.0 1.3 53. 48.5 4.5 .8 .8 46. 5 42.5 - 4.0 4 45 30 o 17.2 16.4 .8 1 45 30 16.4 15.6 - .8 .0 222. 5 61.0 0.0 o 157.0 156.0 1.0 152.2 148.0 - 4.2 3.4 3.3 5 15 30 145. 5 144.9 .6 221.5 66.0 3.2 ffi .143. 139.3 3.7 3.1 3.0 137.5 137.0 .5 118 REPORT OF PROFESSOR EASTMAN. TABLE X. ACTINOMETER OBSERVATIONS, AUGUST 7, 1869 Continued. 9 C c -a fad i _^ Sun '5 a = v ,t Hour. Period of expo Shade First reading. Second reading. Change Solar eft'ect. s J "*- o Q Pi Temperature liquid. Sfc V g . -5 rt 1 Mean solar eft In sun. In shade. A. m. s. s. mm. mm. mm. mm. mm. mm. o mm. mm. 122.5 120.8 1-7 117.0 111.0 - 6.0 . 4.3 4.2 5 30 30 O 116.5 114.8 1.7 221.5 65.0 4.0 100.5 95.0 5.5 3.9 3.7 O 91.0 89.5 1.5 O 51.5 50.3 1.2 48.0 43.0 5.0 3.9 3.8 5 50 30 O 39.0 38.0 " 221.5 62.0 4.3 33.8 28.0 i 5.8 4.9 4.8 o 25.3 24.5 -.8 o 3.4 3.3 .1 3.0 2.6 .4 .2 .2 600 30 2.4 2.2 .2 221. 5 55.0 0.2 2.0 1.6 .4 .2 .2 1.0 .8 .2 i Curve II ou Plate VIII is a graphical representation of tlic changes in the heating power of the sun on the day of the eclipse. The following table exhibits the observations with the photometer on August 7. The observa- tions ou July 20 were made in a similar manner, but only the results are given in Table IX. The numbers tabulated below indicate revolutions of the pinion head, which, when the aperture is open o its maximum size, reads 0.21 rev., and when completely closed reads 1.96 rev. TABLE XI. /i. MI. r. /(. HI. r. 1.76 1.75 1.82 1.78 1.82 2 30 1.76 August 7 11 a. m. 1.80 1.72 1.79 1.77 1.76 1.71 1.73 1.70 1 30 p. in. 1. 72 3 1.72 Hazy. 1.77 1. 77 1.76 1.77 1.77 1.74 1.76 1.75 2 1.70 3 30 1.74 1.77 1.73 1.80 1.70 OBSERVATIONS OF THE ECLIPSE OP AUGUST 7, 1809. TABLE XI Continued. 119 /i. HI. r. li. in. r. 1. 75 1.42 1.71 1.42 3 50 1.G9 4 55 1.44 1.80 1.38 1.78 1.42 1.68 1.59 1.70 1.70 40 1.67 5 5 1. 58 1.74 1.64 1.69 1.70 1.68 1.74 1.70 1.74 4 10 1.64 5 15 1. 69 1.63 1.74 1.69 1.65 1.51 1.64 1.60 Considerable increase 1.67 4 20 1. 52 of cirri and haze over 5 30 1.65 Hazy. 1.57 the sun. 1.67 1.57 1.60 1.64 1.60 1.67 1.59 4 30 1.63 5 45 1. 66 Haze and cirri. 1.66 1.61 1.65 1.68 1.56 1.71 1.50 1.71 4 35 1.54 60 1. 70 Quite clear. 1.60 1.69 1.54 1.69 4 46 "Star"invisihle. Variations in the area of the aperture admitting light. TABLE XII. 7i. m. Area. It. m. Area. August 7 11 0.02 August 7 4 20 .12 1 30 .03 4 30 .06 2 .03 4 35 .12 2 30 .03 4 55 .18 3 .04 5 5 .12 3 30 .03 5 15 .04 3 50 .03 5 30 .06 4 .04 5 45 .07 4 10 .05 C .04 Using the quantities in the above table as linear ordinates, the variation of light on the 7th of August may be graphically represented as in the curve in Plate VIII. 120 REPORT OF PROFESSOR EASTMAN. TABLE XIII. METEOROLOGICAL, OBSERVATIONS, AUGUST 7, 1839. Maximum thermometer Minimum thermometer Hour. Barometer. Thermometers. Clouds. Portion cloudy. Wind. Dry. Wet. Solar, Direction. Force. h. m. in. o o o 9 29. 35 63.8 59.3 108.0 C. K. Hazy 2 SE. 3 10 .33 67.0 61.1 118.0 C. K. Hazy 2 SE. 3 11 .33 70.8 63.0 122.7 C. K. Hazy 1 SE. 3 Noou .31 73.0 64.0 127.0 C. K. Hazy 1 SE. 2 1 .31 73.5 63.5 130.5 C. K. Hazy 1 SE. 2 2 .30 74.0 63.8 127.0 C. K. Hazy 1 SE. 3 2 30 .28 73.3 63.3 121.8 C. Haze 1 SE. 2 3 .28 74.0 63.5 119.0 C. Haze 1 SE. 2 3 30 .27 74.0 63.5 118.5 C. Haze 1 SE. 1 3 50 .27 73.0 63.0 107.0 C. Haze t SE. 1 4 20 .27 71. 5 62.5 88.8 C. Haze 1 SE. 1 4 30 .27 70.5 62.0 79.0 C. Haze 1 SE. 1 4 35 .27 70.2 61.7 75.0 C. Haze 1 SE. 1 4 46 72.0 C. Haze 1 SE. 1 4 55 .28 69.3 61.5 68.5 C. Haze 1 SE. 2 r> so .27 69.5 61.7 83.0 C. Haze 0.5 SE. 1 5 40 .27 68.9 62.2 81.7 C. Haze 0. 5 SE. 1 6 .27 68.8 61.8 78.8 C. Haze 1 SE. 1 76. 53. REPORT DR. EDWARD CURTIS, U. S, A, 16* REPORT OF 1)11. EDWARD CURTIS, U. S. A. SURGEON GENERAL'S OFFICE, Army Medical Museum, Washington, D. C., November 6, 1869. GENERAL: I have the honor to submit the following report on the photographic observations of the total solar eclipse of the 7th of August last, made by the expedition from this office, under my charge. In response to a request from the Superintendent of the United States Naval Observa- tory, accompanied by an offer of a suitable telescope and chronometer, I received on the 14th of May last, through your office, an order from the War Department, directing me to proceed, in com- pany with an astronomical expedition from the Observatory, to Des Moines, Iowa, for the purpose above mentioned, of taking photographs of the solar eclipse. Hospital Steward A. E. Le Merle and Private M. S. Breunan, United States Army, both on duty in the Surgeon General's Office, were directed in the same order to accompany me as assistaiits, and, in addition, the services of Mr. E. J. Ward, a photographer of Washington, were secured for the occasion. I. SYNOPSIS OF OPERATIONS. The members of the party, leaving Washington at different dates early in July, met at Chicago July 8 and reached Des Moines July 10. The boxes containing the photographic apparatus, which had been previously expressed from Washington to Des Moines, we found awaiting us on our arrival. A site for a temporary observatory was immediately selected near the northeastern limit of the city, but, owing to the incessant rains for a week following our arrival, the erection of the building was so delayed that it was not ready for occupation before the 20th instant. Four days were then con- sumed in unpacking the boxes, mounting the telescope, fitting up the dark-room, and preparing the chemicals for use. 'On the 24th of July the first sun picture was taken, and from this date until the 7th of August every fair afternoon was spent in experimenting and practicing with our instru- ment. Of the negatives obtained on the 2Gth and subsequent days one from each day's work has been kept as a record of the appearance of sun-spots. On the 7th of August six negatives of the sun, of which also one has been preserved, were taken early in the afternoon for the purpose of testing the condition of the chemicals, and on the occasion of the eclipse one hundred and twenty- two exposures were made, as follows: two immediately before the time of first contact, fifty-nine during the partial phase between the periods of first contact and the commencement of totality, two during the total obscuration, fifty-seven between the times of reappearance of the sun and last contact, and two immediately after the latter event. Of these negatives three of the partial phase following totality were spoiled, leaving a total of one hundred and nineteen plates actually secured. One negative of the sun was also taken each afternoon for two days following the eclipse days that were spent in varnishing and packing the negatives and precipitating the silver baths for transportation. Two more days were consumed in dismantling the observatory and packing up for departure, and on the 12th of August the expedition started on its return. In connection with the solar photography a series of experiments was also instituted to deter- mine photographically the relative amount of actinic force exerted by the sun at different altitudes. These experiments -were made on eight separate days, and comprise seventy-nine photographic tests of the sun's chemical power. Stereoscopic and other views of the observatory and neighboring scenery, the instruments, and members of the expedition at their various duties, were also taken at odd moments by Messrs. Le Merle and Ward. 124 REPORT OF DR. CURTIS. To sum up, the material results of the photographic expedition arc as follows: eleven negatives of the sun, representing the appearance of that body on as many different days; one hundred and nineteen negatives of the solar eclipse of August 7; seventy-nine photographic paper slips showing the relative actinic force of the sun at different altitudes on eight separate days; twenty- three stereoscopic and other negatives. In accordance with your instructions, the eclipse negatives will be placed at the disposal of the Superintendent of the Naval Observatory for the reading off of the astronomical information which they contain. On the completion of this work they will be deposited, with the other results of the expedition, in the Army Medical Museum. The following is a detailed description of the apparatus and methods of procedure followed in the photographic work, an account in full of our operations, and a discussion of the results obtained : II. THE TELESCOPE. The telescope used was the large equatorial of the United .States Naval Academy, at Annapolis, Maryland, which was loaned to the Naval Observatory for the expedition, at the request of Commo- dore Sands, by Vice-Admiral I). D. Porter, United States Navy, superintendent of the Academy. This instrument is a refractor, constructed by Alvau Clark & Sons, of Cambridge port, Massachusetts, in 1857. It has an object-glass of 7.75 inches clear aperture and nine, feet six inches local length. The tube is mounted eqnatorially, in the German style, on a solid cast iron pier, provided with a spring- governor driving clock. The tinder of the instrument is a small telescope, with an object glass of 1.7 inches clear aperture and 20.25 inches focal length. This telescope, having been received at the Naval Observatory in Washington in .May, was mounted temporarily in a wooden shed on the, grounds of that institution, .and there fitted up for photographic use. For this purpose the, following apparatus had to be made: 1. A heavy wooden cross for the pier of the telescope to rest upon. 2. A camera-box to be attached to the eye end of the instrument and fitted up with two differ- ent arrangements for making the exposures, one to be used during the total and the other during the partial phases of the, eclipse. 3. A diaphragm carrying two position wires crossing at right angles, to be adjusted in the eye- piece. 4. A clamp to hold the eye-piece immovable in its tube after adjustments for focus and angle of the position wires. 5. Diaphragm caps of different sizes to reduce the aperture, of the object-glass in photographing the partial phases of the eclipse. C. New weights for the driving clock, the old ones being too long to use conveniently. 7. A new suspension-piece for the pendulum of the clock to rest upon. This change was required from the fact that, there being no arrangement for altering the position of the polar axis, the pier itself had to be tipped up to make allowance for the difference in latitude between DCS Moines and Annapolis. A new suspension-piece was therefore needed for the pendulum, to suit the altered position of the pier. All these additions to the telescope were made under the immediate supervision of Professor William Harkness, United States Navy, the brass work being done by Mr. W. F. Gardner, instru- ment maker at the Observatory, who worked most zealously that everything might be completed in amide time for an early departure for the West. Four plate-holders and a frame carrying a ground- glass screen were also prepared under my own direction. The camera-box requires special description. In devising this piece of apparatus the first ques- tion that presented itself was whether to use the focal image of the object-glass alone to produce the sun-pictures or to enlarge it by the interposition of a Huyghenian eye-piece. The answer was emphatically given in favor of the latter plan, for the following reasons : In the first place, it could only be by means of an eye-piece that position ^ires could be used and depicted upon the plates, and without these the value of the negatives of the partial phases for astronomical purposes would be greatly impaired ; in the second place, a fair size for the sun-pictures was considered an important consideration in the partial-phase negatives as conducing to greater accuracy in the niicrometrical 1869. 125 measurements, and iii those of the totality as giving such dimensions to the red protuberances that points of structure and detail iu those bodies might bo caught and recognized without the necessity of subsequent enlargement of the negative, an operation that, iu my judgment, is always to be avoided. The only drawback to the use of an eye-piece was the comparatively long exposures required in consequence during totality, making it possible to obtain but few photographs of that phase ; but I considered that even one negative, showing the structure of the red prominences ou a comparatively large scale, would be worth a dozen little images where nothing but the mere posi- tion of the principal protuberances could hope to be shown. It was therefore decided to use an eye-piece, to employ negative plates seven inches square, and to place them at such a distance from, the eye-piece that the image of the sun projected upon them should be as nearly as possible four inches in diameter. To meet these requirements a long slightly - lapering camera bo.v, with square ends, was constructed. This was made in two parts, the joint running lengthwise, with the smaller end fitted to clasp the telescope tube tightly around its entire circumference at two places eleven inches apart, wheu the two halves of the box were screwed together upon the instrument. This fastening was accomplished by stove-bolts passing through solid lugs of wood which projected from the sides of the box along the line of junction of the two halves. The posterior or free end of the camera was fitted to allow the plateholder to slide in upon a slip of glass let into the wood, the holder being then held in position by the pressure of two strong brass springs from behind. The various uprights of the framework at this end of the box were so made that in all cases two projecting arms from each half of the box should, when the latter were fitted together, slide past each other so as to admit of being screwed into one piece, thus making the framework solid and light-tight. The arrangement for making the exposures was as follows: About two and a half inches beyond the end of the eye-piece was a fixed partition across the camera box, pierced with a central aperture just large enough to admit the entire cone of rays from the instrument. Immediately in front of this, passing through rebated slots in the sides of the camera box, was a movable wooden slider long enough to project several inches beyond the sides of the camera, and pierced with two apertures, either of which could be centered with the hole in the fixed partition by simply running the slider to or fro a few inches. In either position of the slider it was held in place by a spring bolt on the side of the camera. One of these apertures for use during totality was fitted up with a light brass shield turning laterally on a pivot, by means of which the hole could be covered or uncovered, the shield being operated from without by being attached by a catgut cord to a little cylinder surmounted by a milled head fixed at the free pro- jecting end of the slider. A stop was originally provided to limit the swing of the shield when thrown aside to expose the aperture beneath, but, finding that the striking of the shield upon it produced a sensible jarring of the telescope, the stop was removed. The other aperture to allow of instantaneous exposures during the partial phases was covered by a rectangular brass plate running freely on guide-rods and pierced with a transverse slot half an inch in width, which was adjustable to a slit of any dimensions by means of a secondary slotted plate, attached to the first by screws. Instantaneous motion of this plate across the aperture was effected by a fine steel wire spring coiled around one of the guide-rods; and when drawn up against the spring the plate was held by a wire loop catching over a little pin which projected upwards through a bridge from the upper surface of a spring trigger, also placed at the free end of the slider. A light touch upon this trigger then released the plate, when the rapid flashing of the slit across the aperture in the slider effected the exposure; and by pressing the trigger always at a predetermined second of time, with eye and car upon a chronometer standing close by, the timing of the exposures could be made with the utmost accuracy. The accompanying figure represents the wooden slider, fitted, as described, with the apparatus for making the exposures. 126 REPORT OF DR. CURTIS. The tube of the telescope being adjusted to the position it would occupy during the eclipse, tlu> camera box was clamped upon it in such a manner that the plateholdcrs and the wooden slider should run in from the side with the lower edges maintained horizontal. On the top of the camera box as thus placed the finder of the telescope was mounted. At a suitable distance behind it was an upriglt of wood carrying a slip of ground glass with a circle drawn on it, to serve as a screen on which to view the image of the sun from the finder when adjusting the telescope. To provide for the fainter image of the corona during totality, a movable screen of white card-board was made to slip over the ground glass, so as to give a more brilliant surface for the reception of the image. On this also a circle was drawn to center the image by. In the under face of the camera box a door was cut to permit the hand to reach the eye-piece, in adjusting the latter for focus and angle of the position wires. The accompanying woodcut, from a photograph by Mr. Le Merle, shows the telescope as it appeared when in actual use in the afternoon. The chronometer is seen strapped to a tripod stand close to the camera box, and the operator is represented in the act of timing an exposure, the end of the slider carrying the trigger being beliiud the camera, and therefore not seen in the cut. OBSERVATIONS OP THE ECLIPSE OP AUGUST 7, 1869. 127 III. THE OBSERVATORY. A site for a joint temporary observatory at Des Moiues, to serve both for my owu party and for Professors Harkuess and Eastman, was selected on a piece of high ground at the northern limit of Second street. This offered the advantages of as close an approach to the central line of the eclipse as possible, a clear horizon in all directions, a well of good water close by, freedom from dust, and good drainage. The exact position occupied by the photographic equatorial, as determined by Professor Harkness, is as follows: latitude, 41 35' 36"; longitude, I u 6 m 16 s .05 west of center of dome of United States Naval Observatory at Washington ; height above the level of the sea, 831 feet. On this site a rough board building thirty-two by sixteen feet was erected, running nearly north and south in the direction of its length. The entire building was floored, and from the northern end an extent of seven feet was partitioned off for the dark-room and ceiled on a level with the eaves. The remainder of. the building was one large room, with the western slope of the roof and upper portion of the western wall not boarded, but covered by a canvas roof which could be rolled up when the telescopes were to be iised. The dark-room was furnished with seven negative baths, standing in a long trough filled with water to keep them cool, a sink composed of a common wash-tub with an India-rubber waste-pipe attached, a barrel of water standing on a platform outside the building with a pipe closed by a stop-cock projecting through the wall, and a large flxing-bath composed of a wooden trough with grooved sides like a negative rack, capable of holding one hundred and fifty plates and filled with a very weak solution of hyposulphite of soda. The room was provided with ventilators on a level with the floor and in the ceiling, and in the partition wall adjoining where the telescope stood were two little dumb-waiters by which the plate-holders could be passed in and out of the dark- room without the admission of light or the necessity of any of the operators moving from their places. Plate I, from a photograph by Mr. Ward, gives a view of the observatory with the canvas roof rolled up and the telescopes ready for use, and Plate II, from a drawing by Mr. Le Merle, shows the arrangement of parts. IV. PRELIMINARY EXPERIMENTS. The telescope being ready for use in June, we immediately commenced our self-taught lessons in celestial photography. These preliminary experiments, commenced in Washington, were con- tinued after our arrival in Des Moines, and were for the purpose of determining the chemical focus of the optical combination, selecting the most suitable photographic formula; for the special work, studying the subject of lengths of exposure both for the partial phases and for totality, deciding upon a plan of operations to be followed during the eclipse, and drilling ourselves thor- oughly in our respective duties, so that there, might be -no mistake or contretemps at the critical moment. 1. Determination of the chemical focus. I confess to having had a great deal of anxiety about the photographic performance of the telescope, both on account of the object-glass being an ordi- nary achromatic lens not corrected for photography and on the score of the additional confusion that must arise from the use of an eye-piece. I was fearful that with such a combination no adjustment of the focus would give a picture sufficiently sharp for exact micrometrical measure- ment. The first day's trial, however, removed my doubts, for with a two-inch diaphragm cap over the object-glass the sun picture came up beautifully sharp as soon as the chemical focus was found. This focus was determined experimentally by sliding the eye-piece to and fro until the best photographic effect was produced. And since the curvature of field affected slightly the definition at different distances from the center of the plate, that position of the eye-piece was selected, in order to secure the best mean focus, which should give the sharpest definition midway . between the center and limb of the sun's image. Using, then, as a test object, a large sun-spot that happened to occupy just this position on the solar disk, the proper adjustment of the eye- piece for the required focus was determined with great care and recorded. But this determination being made with a two-inch diaphragm cap over the object-glass, it was necessary to test also the performance of the full aperture of the lens with the same focus, since this aperture would be used 128 REPORT OF DR. CURTIS. during totality. For this purpose solar negatives were taken .just before sunset, when the feeble actinic force of the sun permitted the whole diameter of the object-glass to be used without over- exposure of the plates, and it was found that with this aperture the definition was not nearly so good as when the two-inch diaphragm cap was employed, but that the focus could not be improved. 2. Selection of photographic formula. In deciding upon what formulae for bath, collodion, and developer to use during the eclipse, regard was had exclusively to the peculiar phenomena of total- ity, since the sun negatives during the partial phases, intended solely for micrometrical measure uient, could be obtained equally well by any process. The subject presented peculiar difficulties, since it involved representing upon one plate, if possible, the corona, possessing very feeble actinic power, and the red protuberances, which, on the contrary, exert a very strong photographic action. Desirous of knowing how far this difficulty had been overcome by previous operators, I obtained copies of Dr. Vogel's photographs of the eclipse of 1868 in Arabia, and through the kindness of my friend, Dr. R. L. Maddox, of Southampton, England, and the courtesy of Mr. Richard Beck, of London, was also furnished with prints of Mr. De La Rue's negatives of the totality in the eclipse of 1860 in Spain. In both cases the prints were from enlarged negatives, which was to be regretted, for in such pictures much of the detail of the original negative is infallibly lost. An examination of these prints showed in the photographs of De La Rue a very faint corona, with the prominences nevertheless so dense that but little detail in them could be made out. The Arabian pictures presented the same characteristics still more strongly marked, the corona being scarcely visible at all, while the red protuberances appeared as mere masses of white upon a black ground. In the latter instance much of the effect described may have been due to bad weather; still I could not help believing that in both cases collodions had been used that gave brilliant pic- tures of great intensity rather than soft negatives full of detail, and that, by a selection of chemi- cals that should produce the latter effect rather than the former, much better results might be obtained. The subject was fully discussed with Mr. Le Merle, a practical photographer of long experience, to whom the preparation of the chemicals was intrusted, and he, entertaining the same views, felt confident that with a collodion of his own, containing a full proportion of bromide, a sufficient exposure, and careful development with a moderately strong developer, negatives could be secured that would show detail in the prominences and give a fair indication of the corona as well. Accordingly he prepared his solutions by the following formulae: COLLODION. Iodide of ammonium ."> grains. Iodide of cadmium 5 grains. Bromide of cadmium 5 grains. Atxvood's alcohol, 95 per cent. 1 fluid ounce. Sulphuric ether 1 fluid ounce. Pyroxyline, (Anthony's negative,) enough to give the proper consistency. The collodion intended for use during the eclipse was made in a large stock bottle on the 29th of July, and on the fifth of August was brought to a lemon yellow color by addition of tincture of iodine. BATH. Nitrate of silver, recrystallized - 40 grains. Distilled water - 1 fluid ounce. Nitric acid, C. P., sufficient to make the bath work clean under a long development with the above collodion. The bath solution was made five days before the eclipse, was dosed with the proper amount of iodide of silver in the usual way, and was worked a little each day. DEVELOPER. Saturated solution of sulphate of iron 1 fluid ounces. Acetic acid, No. 8 1 fluid ounces. Water ... 13 fluid ounces. OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 129 The delicate beauty of the totality negatives obtained, which, while showing considerable of the corona, are full of detail in the prominences, proves the soundness of the views entertained and the excellency of Mr. Le Merle's formula' for producing the desired result. 3. Estimation of the length of exposures. The exposure during the partial phases was simply a matter to be decided by direct experiment upon the sun, and it was found that while a two-inch aperture to the object-glass gave abundant exposure in the middle of the day, this had to be some- what increased as the afternoon, advanced and the sun approached the horizon. The width of the slit in the instantaneous plate found necessary varied from a quarter to half an inch, but while this may seem excessive, it must be remembered that the plate was about an inch and a half from the eye-piece. The question of the length of exposure to be given to the plates during totality, was, on account of its great importance, made the subject of careful study and experiment. As a basis for this esti- mation I determined to rely exclusively on the teachings of De La Eue's totality pictures of the 1860 eclipse, considering these as the most satisfactory photographs of the phenomenon in existence. This astronomer's result afforded two ways of making the estimate. The first depended upon his calculation of the relative photographic intensity of the light from the red prominences and full moon. This calculation he made as follows : * During the taking of his second totality picture the telescope was shaken and three impressions of the prominences appeared. From their relative intensity he inferred that the faintest of these received twelve seconds' exposure. Attempting to photograph the full moon with the same instrument used for the eclipse he obtained an " extremely faint impression" after an exposure of three minutes. This impression he estimated to be one- twelfth the intensity of the faintest of the impressions of the prominences above referred to, an esti : mate which makes the relative photographic power of the full moon and solar prominences as 180 to 1. Taking this estimate for what it was worth, and inferring (though De La Eue does not so state) that he photographed the full moon when at nearly the same altitude as the sun during the 1860 eclipse, I determined to try the full moon with my own telescope and see what length of expo- sure would be necessary to produce a fair impression of that satellite when at an altitude of about 26, the position that the totally eclipsed sun would occupy on the 7th of August. Dividing this time by 180 should then give the time necessary to produce a correspondingly strong impression of the prominences. The full moon occurred at 8 h 30 m p. m., Washington mean time, on the 23d of June, but that evening was unfortunately cloudy, so that the experiment could not be made till the following night, when the moon of course was many hours past the full. It was then found that at 26 above the horizon five minutes produced a weak image, ten and fifteen a better, and twenty an image that came up promptly under the developer. But since there was no means of allowing for the moon's motion in declination during these long exposures, the pictures were necessarily mere blurs, and it was very difficult to say exactly what was the correct exposure. Moreover, when it came to an exposure of twenty minutes, five minutes more or less seemed not to make any great difference in the strength of the image. These experiments were therefore exceedingly unsatisfac- tory ; and considering also that De La line's original calculation of the comparative actinic force, of the light of the moon and the red flames was, though the best that could be made, yet necessarily rather loose, I determined to abandon altogether this method of estimating the totality exposures as untrustworthy, and to rely exclusively upon the second method afforded by De La Rue's labors, that, namely, of calculating directly from the exposures he gave his own totality pictures in Spain. This was a very simple matter. In the first place, I proposed to follow his plan of using an eye-piece to magnify the focal image of the object-glass, and moreover to represent the sun upon the photo- graph of the same size as in his pictures. So far as the telescopes were concerned, therefore, the exposures to produce like effects should be exactly proportional to the size of the instruments; that is, inversely as the areas of the object-glasses. Now, the object-glass of the Kew photo-heliograph is 3.4 inches in diameter, that of the Annapolis equatorial 7.7/5 inches ; or, in other words, taking the proportion of the squares of these diameters, my equivalent exposure should be slightly less than one- fifth that of De La Eue. An exposure, that is, of eleven and a half seconds with my telescope should, other things being equal, produce the same result as the one-minute exposure given by De La Eue. I say " other things being equal," because an important consideration has been disregarded in stating ' I'liilosopliiriil Transactions, 18(52, l>ag' 405. 130 REPORT OF DR. CURTIS. this estimate, namely, the effect oil the necessary length of exposure of the dilfereut altitude of the sun on the occasion of the two eclipses. In De La Hue's case the sun was near the zenith, whereas in the 1869 eclipse it would be but 26 above the horizon. In proportion, therefore, to the sun's loss of actinic force when at this altitude the estimated exposure for the totality whould have to be increased. In order to determine exactly what this loss was I began experimenting by testing the length of exposure necessary to produce negatives of the sun of equal intensity at mid-day and at a quarter to five in the afternoon. But owing to the latitude that always exists in exposures of negatives by the wet collodion process, I soon abandoned this method as too coarse and uncertain, and resorted to comparative exposures of photographic paper. These were made in the following way : A strip of sensitized paper was tacked to a board and covered by a sheet of yellow paper in which were cut out twenty-seven rectangular spaces. The board, covered by a velvet cloth, was set up so as to exactly face the sun, when at a given second, timed by the chronometer, the vel- vet was whisked away, and by means of narrow strips of wood the rectangular spaces were suc- cessively and suddenly covered over at definite periods of time, thus effecting a different length of exposure for the sensitive paper under each space. Such a series of exposures was made at differ- ent hours of the day, the times of exposure being invariably the same. These times were as fol- lows, the numbers meaning seconds : , 1, 2, 3, 4, 5, 7J, 10, 12i, 15, 17J, 20, 25, 30, 35, 40, 50, 60 ; and also, when the light was feeble, 80, 110, 150, 200, 260, 330, 410, 500, 600. Then by taking the slip exposed at noon as a standard, and matching shades with those exposed at other hours, the relative amount of actinic action exerted by the sun was roughly calculable. That is, if at 5 h p. in., for instance, the space exposed for ten seconds is identical in shade with that exposed for five sec- onds at noon, and if the proportion holds good in the other spaces, the reasoning is that at that hour the sun's actinic force, as measured by the photographic effect produced, is one-half that at noon. But not to rely upon any single comparison, the shades in any one slip.were, in all cases that would admit of it, matched at least as high as the shade produced by an exposure of fifty or sixty seconds, and the mean of the results obtained from these various comparisons was taken as the expression of the sun's chemical power at the time.* * It is proper to state that neither at the time of making these experiments nor of writing the above had I read of Professor Roscoe's critical observations of this character at Manchester, England, (I'hil. Trans., 1863, p. 139, and 1865, p. 605.) It will be seen that my own was a rough method of applying the same principles as those involved in Profes- sor Roscoe's elaborate and admirable arrangement. The question as to the relation between length of exposure and chemi- cal intensity of light in producing identical shades of blackening I had also experimented upon, in order properly to interpret the results of the photo-chemical observations, and had reached the same conclusions that Professors Bunseu and Roscoe had previously arrived at, nnconsciously verifying, by a different experiment, the law of this relation dis- covered by them and thus announced: (Phil. Trans., 1863, p. 145.) " Equal products of the intensity of the light into the time of insolation correspond, within very wide limits, to equal shades of darkness produced on chloride-of-silvcr paper of uniform sensitiveness." My plan of experimenting on this subject was rough and simple, like that of the other actinometrical observations, but quite effective. A sensitized paper strip was first exposed at noon in the precise man- ner described above in the text, different spaces on the strip receiving different, lengths of exposure, and care being taken that the surface of the paper should be exactly at right angles to the course of the solar beam. Immediately afterwards a second strip was exposed, the board to which it was tacked being, in this case, inclined to the direction of the sun's rays at such an angle that the shadow of a strip of cardboard projecting from the face of a box previously carefully adjusted so as to exactly face the sun, should, when falling from the board immediately under it, measure twice the actual width of the cardboard itself. Under these circumstances each space of this sensitized strip received, of course, but one-half the amount of sunlight that impinged upon those of the first strip, and a comparison of the two strips showed that in all cases double the length of exposure was required on the second strip to produce degrees of blacken- ing identical with the shades of the first. The actinometrical experiments described in the text, -which were undertaken, as then 1 stated, for the purpose of estimating the length of the totality exposures, led me, by their interest, into making something of a series of them in order to test, approximately, the chemical force of the sun at all altitudes. One day, the 29th of July, was entirely given up to this work, and photographic observations were taken from sunrise to sunset at every fifteen minutes during the morning and afternoon, and every half and whole hour during the middle of the day. Although from the compara- tively rude character of the method of observation the results obtained can only be considered as rough approximations to the truth, yet they are sufficiently accurate for the purposes of a practical photographer in estimating lengths of exposure for negatives, and possess, it is believed, so far as they go, a peculiar value on account of the unusually cloud- less skies and equable condition of the atmosphere in that splendid Iowa climate during the period through which the observations extended. A table of the results of the observations is accordingly given in Schedule B. Though for the sake of avoiding error as far as possible the slips of each day were invariably compared with the noon shade of the same day as the standard, yet these mid-day slips have been found to differ so rery slightly from each other in most cases not OBSERVATIONS OF THE ECLIPSE OF AUGUST T, 1869. 131 A general meau of observations of this character, made on seven different days at or iiear the time at which totality would occur, gave for the sun's actinic force at that period 0.374, the chem- ical intensity at noon being taken as 1.000. But since a collodion plate is probably not so sensi- tive to a diminution of chemical force in the light as silvered paper, I considered it safe to estimate that, on account of the time of day at which totality would occur, the calculated exposure should be just doubled. The difference in time of year and latitude between De La Hue and myself on the occasion of the two eclipses being too inconsiderable to affect the question of length of exposure, I thus obtained twenty-three seconds as the equivalent with my telescope of the one-minute exposure given by that astronomer. With this estimate I had to allow on the one hand for the fact that De La Rue's negatives were considerably over-exposed, and as an offset on the other for the considera- tion that I did not propose to use such very sensitive chemicals as he describes his to have been. Weighing these two considerations against each other, I estimated that about ten seconds should, under the circumstances, yield a negative properly timed for the protuberances, upon which, by the help of Mr. Le Merle's well-bromized collodion, the corona might also be shown to some extent. I accordingly determined to give the first plate this exposure, designing this negative especially for the prominences, which would of course be seen to best advantage during the first and last few sec- onds of duration of totality. The second plate, to be exposed while the first was in process of devel- opment in the dark-room, I determined should have from thirty to forty seconds, for the purpose of representing the corona. After these two I would, of course, be guided by word from the dark- room. How these estimates were modified on the occasion of the eclipse, on account of the bad weather, will be detailed further on. 4. Plan of operation* during 1lte edi])ne. After experimenting to see how best to dispose of our force, and divide the labor during the eclipse, we settled down to the following plan, which was strictly followed: The first operator, Mr. Ward, was to coat the plates and put them into the baths; the second, Mr. Brennan, to take them out, wipe their backs, place them into the holders, and pass the latter out to me by means of one of the dumb-waiters in the wall. My own duty, as third ope- rator, was to take the plate-holder from the dumb-waiter, place it in the camera, draw the slide, adjust the telescope, (whose position was invariably disarranged by shifting the holders,) expose at a predetermined second of time by a chronometer standing at my elbow strapped to a tripod stand, return the holder to the dark-room by the second dumb-waiter, and then record the instant of the exposure on a sheet of paper tacked to a shelf. The fourth operator, Mr. Le Merle, was to take the plate from the holder when returned to tlie dark-room, develop, wash, and drop it into one of the grooves in the large fixing trough. There the plates were to remain, slowly fixing, until the eclipse was over, when they were to be taken out in the exact order in which they had been put in, washed, and numbered with a diamond , By this even distribution of labor, and by the help of the dumb- waiters and the large fixing trough, we found upon trial that we could take negatives at the rate of twenty in fifteen minutes. But desiring that all the operations should be performed with perfect deliberation, and conceiving that the number of negatives that would be taken during the eclipse at the above rate was unnecessarily great, I determined to limit the exposures to one each minute, (except at the times of first and last contact and during totality,) so that all the operators having ten or fifteen seconds to spare with each plate could do their work coolly and carefully. For total- ity, the arrangement was that at two minutes before the time of its commencement I was to cease exposing and call "Prepare for totality." All three operators in the dark-room were then to take out plates from the baths and rapidly fill all four of the plate-holders. Brennan, then leaving the dark-room, was to assist me at the telescope by handing me the holders, taking them again from me, and recording the times of exposure as I called them out from the chronometer. This plan was on the supposition that, with a clear sky and with exposures varying from ten to forty seconds, four or five negatives might be secured during the duration of the total phase. While developing the first totality negative it was also Mr. Le Merle's duty to judge, as soon as possible, by the manner in which the image came up under the developer, what modification in the exposure for the promi- at all that the results obtained on different days an' quite comparable with each other. lu the ease of the observa- tions on the 3d of August, however, allowance must be made for the fact that the standard slip was not exposed till after three o'clock in the afternoon, at which time, as the results of other days show, the diminution of chemical inten- sity of sunlight has commenced. The two slips exposed on July 27 are only comparable between each other on account of the hazy atmosphere of that day. 132 REPORT OF DR. CURTIS. nences should be made iu the succeeding plates, and to call out .the same lor my guidance. During the two minutes, also, covering respectively the times of the first and last contacts, it was suggested by Professor Harkuess to take negatives as fast as they could be run through the camera, and accordingly the same plan as for totality was adopted for these occasions, with the addition that Professor Harkness, being then at leisure from his own duties, should assist by attending to the adjustment of the telescope, leaving me nothing to do but to shift the plate-holders in the camera and make the exposures. V. THE ECLIPSE. For three weeks before the 7th of August the weather had been magnificent, day following day with the sun unobscured from rising to setting, and the atmosphere beautifully clear. But at sun- set on the 4th the west was streaked with ominous "mare's tails,'' and for the following forty-eight hours the sky was overcast with rain-clouds, the air loaded with moisture, and the wind strong from the northeast. The morning of the 7th dawned upon a similar day. but before eight o'clock the wind shifted to the southeast and the clouds rapidly broke up and cleared away, leaving, however, to my sorrow, a dense ha/e in the air that foretold of long photographic exposures and thin negatives. Our preparations were complete. I had a rope stretched around the observatory at a distance of a hundred yards, and by the kindness of Mayor Hatch, of Des Monies, we were furnished with two special policemen, who performed most thoroughly their duty of keeping beyond this barrier the crowd that nocked to the place in the afternoon. In the photographic line one hundred and fifty plates had been cleaned and carefully inspected, so that all used might be faultless. During the morning the baths were freshly filtered and tested by taking some stereoscopic views; four gallons of developer mixed iu a large jar, and the collodion decanted from the large stock bottles in which it had been ripening into eleven wide-lipped vials of about eight ounces capacity. These were filled about three-quarters full, and were to be nsed in turn till half empty. The dark-room and camera- box were thoroughly sponged out, the plate-holders tried to see if the slides ran free, and all the sur- faces rubbed with paraffine. The paper on which to record the exposures was tacked down to the shelf between the dumb-waiters, and before the commencement of the eclipse two lanterns were lighted and hung so as to illuminate this shelf and my chronometer. Against the wall, near by, were hung memoranda of the exact time of commencement and termination of the several phases of the eclipse, calculated for the chronometer I was to use, by Professor Safford, of the Chicago Obser- vatory, and also of the proportions of the areas of the different diaphragm apertures to be nsed over the object-glass of the telescope, to guide me iu estimating the exposures. As soon as the sun crossed the ridge-pole of the observatory Professor Harkness and I adjusted the eye-piece of the telescope so that the position wires should be approximately at 4f> to a parallel of declination, and clamped it immovably. Then to determine the 1 exact position of the wires, the Professor observed on the ground-glass screen three transits of the sun across each wire. These observations were also repeated immediately after the eclipse was over. As soon as the position wires were set we commenced taking solar negatives, in order to test the amount of exposure that the hazy atmosphere would necessitate, and to be sure of the condition of the chemicals. Every- think worked perfectly at first, but about half an hour before the time for commencement of the eclipse, to our dismay, jet-black spots, such as none of us had ever seen before, suddenly appeared on every plate. These did not come up during development, but only after the water was turned on to icash off the developer. Suspicion at once attached to the well-water with which the barrel was filled, although we had been using it for washing negatives for two weeks with perfect success, and it had worked well that very morning on some stereoscopic plates. A plate was accordingly rapidly exposed, developed, and washed with (Unfilled water. It came up perfectly clean, thus proving the trouble to be in the water. Fortunately, in order to provide against every contingency, I had pre- viously had hauled to the observatory a large cask of cistern water; so we rapidly emptied our barrel of the well-water and filled it from the cask, while Mr. Breunan started off at a run to engage a man to bring more water from the nearest cistern in the neighborhood during the progress of the eclipse, so that there might be no danger of our running short. In the mean time Mr. Ward was coating the batch of plates for the first rapid exposures. Taught by the preliminary practice we had just had, I arranged the telescope with the slit in the instantaneous-plate at its widest half an OBSERVATIONS OF THE ECLIPSE OP AUGUST 7, 1869. 133 inch and with six inches aperture to the object-glass. At 9 h 59"' 57 N by my chronometer I made the first exposure, and passed seven plates through the camera in rapid succession, as had been arranged. An interval of about four minutes then elapsed while Mr. Ward refilled the baths, after which we settled down to our steady work of one plate a minute. At the thirty-ninth plate, Mr. Le Merle calling for more exposure, I removed the diaphragm cap from the object-glass, and from that time on worked with the full aperture, of the lens. As the eclipse advanced and the sun's disk narrowed to a crescent the light became very gloomy, and the air growing suddenly damp and chilly, I was glad to don a coat to prevent shivering. At the same time the image from the finder on the ground-glass became so faint that I was obliged to slip up the white card-board screen that had been prepared for use, during totality. At exactly two minutes before the calculated time for the commencement of that phase I gave the prearranged signal to the operators in the dark-room. The four plate-holders were then quickly filled, and Brennan came out to assist me. A holder was placed in the camera and the telescope was adjusted as well as possible by the fine crescent image of the sun. With my back to the heavens and my eye riveted upon this little image on the white card-board, I watched it shrink to a mere line, and then suddenly melt away in all directions like an icicle thrown into boiling water. With its fading came a solid, rushing darkness, that seemed to grow in the very air and close upon me from all sides, producing a strange sensation as of positive eugulfment by something black and material, whose embrace was all the more thrilling from being- swift, noiseless, and impalpable. Out went the last twinkle of sunlight, and out flashed the light in the lantern swinging by my chronometer, as suddenly as the blaze from a match struck in the dark. The totality had come, and the "Oh! Oh! Oh!" of the distant crowd which had followed the rapid fading of the sunlight changed to one shout of admiration, and was then suddenly hushed. But to me the moment was one of dismay, for, with the vanishing of the sun's image from the card- board screen, a most unexpected difficulty presented itself, which threatened to destroy all chance of making but one exposure during the totality. This was that the image of the corona thrown by the finder was so excessively taint that at first I could see absolutely nothing upon the screen when the sun disappeared. But, as previously mentioned, the telescope required readjusting after each change of plate-holders in the camera, no matter how carefully that operation was performed, and it instantly flashed through my mind, how will it be possible to effect this readjustment after the present plate is removed, if the image from the finder is too faint to be seen ? Fearing, then, that everything would have to be staked upon the single plate already in the instrument, 1 shrank from making the exposure until I could be absolutely sure that in this case, at least, the rather uncertain preliminary adjustment by the fast dwindling crescent of sunlight, was correct. I therefore strained my eyes to the utmost, and at last, by putting my face close to the screen, was able to make out a faint halo of light, defining the disk of the dark moon. Seeing, then, that the centering of the image was very nearly exact as the telescope stood, I wasted no time attempting to better it, but at once threw open the shield to make the exposure. This difficulty of the faintness of the image of the corona was totally unexpected, and the more provoking because, to make sure, as I thought, that I was secure against just this mishap, and that the plan of receiving the image from the finder upon white card-board was safe for use during totality, 1 had previously carefully tested the arrange- ment upon the moon, whose light that of the corona was universally held to equal, and had found that I could see the image of that luminary upon the screen with perfect distinctness when standing so as to command the adjusting-screws of the telescope. Whether it was that the real amount of light of the corona has been overestimated, or whether its feebleness on this occasion was entirely due to the prevailing haze, I cannot, of course, positively say, but am inclined to think that most of the trouble was from the latter cause. After starting the exposure and calling the time by the, chronometer for Brennau to record, I turned to gaze at the heavens. My first feeling, I confess, was one of slight disappointment at the appearance of the corona, which did not look as bright or extensive as I had been led to expect from the various drawings of previous eclipses. It seemed to extend to a distance equal only to one-fifth or one-quarter of the moon's diameter. But the magnificence of the red prominences, and the dis- tinctness with which they could be seen by the naked eye, filled me with astonishment, for I had supposed they would scarcely be visible without a glass, especially to slightly near-sighted eyes like mine. They were, however, readily to be seen, and, instead of being a "pink" or "rose" color, they 134 REPORT OF DR. CURTIS. looked to me of a pure, rick carmine tint, and .seemed to glow and sparkle as if the moon were a disk of jet studded ou its eastern side with rubies or garnets flashing in the sun. Glancing at the surrounding sky, I observed two stars, probably Venus and Mercury, though I made no note of their position. The appearance of the sky was different from what I had expected, the color being rather a leaden bluish-gray than the deep indigo generally observed where the atmosphere has been clear. Of the degree of darkness I can form no estimate; I never once thought of it; and have only a- vague remembrance that after the effect of the first rush of the shadow had subsided it was not really dark. Indeed, I was so intensely absorbed in my work, and so dreadfully anxious for the success of the plate, in the camera, upon which 1 then believed that the only chance of securing a photograph of the totality was staked, that I really paid no attention to anything but the chronom- eter beats, and my impression of the appearance of the phenomena already described is only as of some dimly-remembered dream. Of the landscape and horizon I saw nothing, being shut in by the walls of the observatory. As to the length of exposure to be given to the plate in the camera, the unfortunate weather had, of course, upset my predetermined estimate, and I was obliged, during the progress of the eclipse, to make the following rapid calculation of the additional time that the hazy atmosphere would necessitate. At the thirty-ninth plate, Mr. Le Merle calling for more exposure, 1 was forced to work with the full aperture of the object-glass; that is, I was using an aperture of seven and three-fourths inches in diameter, when two and one-half or three ordinarily sufficed; or, in other words, taking the proportions of the squares of these diameters, I was giving at the time of the fortieth negative from six to ten times the usual exposure. At this rate, then, allowing for the pro- gressive diminution of actinic force as the sun and moon sank lower in the heavens, the totality ex- posures should be at least ten times the original estimates; or, my shortest exposure for the prom- inences should be a minute and forty seconds, and the longer timing intended especially for the "corona would be, of course, impossible. But, from the effect of the progressive motion of the moon in successively covering up the eastern and bringing into view the western prominences, I consid- ered one minute as, imder any circumstances, the longest available time, for an exposure. This amount, therefore, I determined to give the negative, and so notified Mr. Le Merle, warning him, however, that the plate would probably be under-exposed, and that he must do his best by a pro- longed development. As a matter of fact, I ran the exposure six seconds over the minute. After removal of the first a second plate-holder was slid into the camera, though with grave doubts in my mind if it could be used, on account of the difficulty of seeing the image from the finder, by which to adjust the telescope. Again I strained my eyes to the utmost to catch the faint glimmer of light on the screen. At first, as before, the card-board was an absolute blank, but gradu- ally, as the pupils of my eyes dilated, I could see a faint image, and, by dint of turning the adjust ment screws by guess, and then stooping over the screen to see what effect was produced, 1 managed at last to bring the image into tolerable centering, when, without waiting to make the adjustment perfect, I whirled open the shield to make the exposure. But thirty-seven precious seconds had been consumed in this annoying method of adjusting; we were in the last minute of totality; and I listened in great anxiety for word from the dark-room to regulate the length of exposure. Fifteen more seconds passed, when Mr. Le Merle called out, "Double the time," and my heart sank as the inexorable chronometer showed that, instead of double the exposure, this plate must have even less than the first. I believed that the totality pictures would be failures, but, to secure all the effect possible, I ran the exposure of the second plate to within one second of the calculated time for the reappearance of the sun. This calculation, however, proving not to be accurate, the last nine seconds of totality were lost, and I was putting the third holder into the camera when a spark of sunlight reappeared. Kapidly shifting the slider to bring the instantaneous apparatus iuto play again, and adjusting as quickly as possible, I touched off the trigger and secured a negative (No. 64) showing a fine crescent of the sun not over a thirtieth of an inch in thickness at the middle. And now I was cheered by hearing from the dark-room that tinder a prolonged development the totality pictures, which at first seemed to be hopelessly under-exposed, had come up well and showed beautiful detail in the prominences, with a very fair indication of the corona. We now returned to the routine work of one plate each minute, except a break after the ninety-second plate of two minutes, when, OM'ing to the flexure of the long telescope-tube as it swung more and more hori- 1869. 135 zoiital, \ve were forced to stop and readjust the centering of the finder. Near the time of last con- tact, also, the rate was changed, and seven plates were run through the camera as fast as we could shift them, in the same manner as at the commencement of the eclipse. Finally, immediately after the last exposure had been made, Professor Harkness took another set of transit observations on the ground glass screen of the camera, to determine the exact position of the wires in the eye-piece. VI. THE PHOTOGRAPHS AND THEIR TEACHINGS. 1. Photographs of the partial phases. These negatives, one hundred and thirteen in number, (counting out four exposures that prove to have been made immediately before and after the times of the external contacts and three negatives that were spoiled,) were taken solely for astronomical purposes, and form an invaluable series of accurate observations upon the eclipse. Their measure- ment and astronomical discussion belong, of course, to the United States Naval Observatory, and the work, I understand, will be immediately taken in hand by Professor Harkness. The instants of exposure of the negatives were timed touching the trigger of the instantaneous apparatus always at a predetermined even second by an excellent mean-time chronometer, Negus 1275, which was compared daily by Professor Eastman with the standard Negus 1300, whose error and rate in turn Professor Harkness determined by frequent sextant observations. The record of these negatives, as well as of those of the sun taken on other days, is given in Schedule A. As regards the appearance of the negatives from a purely photographic point of view, I cannot but feel some regret that the unfortunate weather should have somewhat marred their beauty. In the first place, the haze required the whole diameter of the object-glass of the telescope to be used, and with this aperture the photographic definition of the instrument was under any circumstances inferior to that afforded with the usual two or three-inch diaphragm cap. Moreover, the haze inter- fered directly with the sharpness of the pictures, the negatives showing a great and interesting difference in appearance, according as the haze was lighter or denser at the times of the various exposures. And the suddenness of the changes in the density of the mist as thus recorded is quite remarkable, two consecutive negatives, taken at minute intervals only, sometimes exhibiting extremes of contrast from this cause. At one time, indeed, the haze was so strong that the atmo- sphere, for some little extent around the solar crescent, was sufficiently luminous to imprint itself on the negative even during the fraction of a second that the latter was exposed. In a large number of the plates the lower portion of the sun is partially obscured, and the sharpness of the limb lost by the effect of a photographically dense belt of haze that hung tenaciously over that portion of the solar disk. These negatives, therefore, cannot be read by the plan of measuring the distance apart of the cusps. But since the effect of lack of perfectly sharp definition upon the main por- tion of the limbs of the sun and moon has been merely to smooth somewhat their naturally rough and uneven outline, the centers of the two disks can be found with as great accuracy as if the defi- nition were absolutely perfect, and by following therefore the method of reading by determining the distance apart and position of the centers, the value of the negatives for astronomical purposes will probably be found not to be in the least impaired by the effects of the hazy weather. These partial-phase photographs exhibit very well a physical phenomenon that has been often noticed before, namely, an apparent increased brightness of that portion of the solar disk imme- diately bordering the projection of the dark limb of the moon. The cause of this easily-explained appearance has, so far as I know, been invariably misconceived by such astronomers as have dis- cussed the matter, its occurrence having been even adduced, most erroneously, as evidence in favor of the existence of a lunar atmosphere.* On account, therefore, of the very important bearings which this simple little glow of light has been made to assume, a thorough understanding of its true explanation becomes quite necessary. The phenomenon, first observed by Professor Stephen Alexander, in 1831, was specially looked for and again found by him in his expedition to Labrador on the occasion of the eclipse of 1860. In his report on that expeditionf he states that it was seen by himself and three other observers, was plainly depicted on the photographs, anil also " is unquestionably pictured in the copies of daguer- '"On the Indications by Phenomena of Atmospheres to the Sun, Moon, and Planets." By Professor Challis. Monthly Notices of the Royal Astronomical Society, Vol. XXIII, page 231. t In the " Report of the Superintendent of the United States Coast Survey for the year 1860." 136 REPORT OF DR. CURTIS. reotypcs of the eclipsed sun taken at Mr. Campbell's observatory in Xew York, under the supervi- sion of Mr. Campbell and Professor Looinis, in May, 1854." The Professor, in his report, offers no explanation of the appearance. The same "bright band" occurred also in Mr. ])e La E lie's photo- graphs of the I860 eclipse in Spain, and was explained by the English astronomer royal, Mr. Airy, after proving that a lunar atmosphere could not produce the effect in question, as being purely a subjective phenomenon, due to the effect of contrast.* This suggestion Mr. De La Eue submitted to experiment t by cutting out half the solar crescent in one of his prints and slipping under the flap thus raised a white background to take the place of the previous black one. Immediately, he states, the bright baud disappeared. Again, upon pasting a black disk partially over the sun's image in an ordinary photograph of that body, he asserts that the bright band instantly sprang up along the line of the artificial moon. He therefore holds with Mr. Airy that the phenomenon is purely an optical illusion. Now it is rather singular, to say the least, that this appearance, if at all as well marked in the 1860 photographs as in those obtained during the eclipse of last August, should have been so sum- marily dismissed from existence and upon the strength of such loose tests as those applied by Mr. De La Eue.f Convinced by the aspect of my photographs that the bright band was not an optical illusion, I re-read De La Rue's account of his experiments in the matter, when it became evident at once that these were not conducted with sufficient precision to be decisive. Thus considering the effect to be wholly one of contrast, De La Euc substituted a background of pure white in place of one of pure black, and found that the brightening disappeared. But here is an important source of error in this method of testing the matter; by using a pure white background a contrast the other way is established, for the white paper is now a bright surface and the gray disk of the solar image a comparatively dark one, so that by the amount of reversed contrast, as it might be termed, the judgment is blinded as to whether the original bright bordering has totally disappeared or merely been so dimmed in effect by the superior brightness of the brilliant white background as to be no longer appreciable by the eye. To make the experiment fair a background should be used of the same tint as the surface upon which the brightening occurs, when, if the latter is wholly subjective, the tint should be uniform across the cut edge. Such a background can be best obtained by cutting off a piece, in the very print to be tested, from the opposite non-eclipsed side of the sun itself and slipping it under the eclipsed edge, previously, of course, cut out from the original black background, so as to exactly complete and fill up the gap in the solar disk originally occupied by the dark moon. With the experiment performed in this way it will be found that the bright band does not disappear, but looks, if anything, more brilliant than before, since now the eye appreciates that there can be no deception and is able to judge absolutely of the true degree of brightness of the little ribbon of light. In a similar manner De La Rue's second experiment is also wanting in thoroughness. To show, as he thought, that the effect could be produced at will by contrasting a bright and dark- surface together, he pasted a black disk so as to partially cover the solar image in an ordinary pho- tograph of the sun when not eclipsed, and states that the print then " showed the brightening very distinctly." But this experiment totally fails to show that the apparent brightening thus pro- duced is as brilliant as that seen in a genuine eclipse picture, and therefore does not prove that the latter phenomenon is wholly of the same nature as the former. To make this experiment also accurate it should be performed by pasting the black-paper disk on the image of the sun in the eclipse picture itself, taking care to cover the same extent of the solar disk on the one side as that actually eclipsed oh the other. If this be done it will be found that the appearance of the faint brightening, produced by contrast along the line of the black disk, (visible to some persons, but which I confess I have never been able to see at all myself,) is altogether inferior in brilliancy and extent to that bordering the line produced by the genuine eclipse. This phenomenon, then, so frequently seen and photographed during a solar eclipse, is, beyond all question, real. To account for its appearance, my first step was to ascertain if it was * Monthly Notices of the Royal Astronomical Society. Vol. XXIV, pp. 13 and 188. t Philosophical Transactions, 1862, page 368. t At the time of writing I had not seen Professor Challis's subsequent papers, (Monthly Notices MI' tin- l.'nval Astro - nomical Society, Vol. XXIV, page 49, and Vol. XXV, page 18,) in which he also calls in question Messrs. De La Rue and Airy's assertion that the phenomenon is purely subjective, though finally assenting to Airy's conclusion llmt the exist- ence of a lunar atmosphere would not account for the appearance. OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 137 peculiar to an eclipse, or would occur, as I rather anticipated, whenever the same optical conditions were reproduced. To answer this question, experiments were made with a miniature artificial eclipse, which I prepared in my optical room at the Army Medical Museum after my return from the West, in the following way : For the sun I used the disk of ground glass that serves as the source of illumination for photographing certain characters of microscopic objects. This disk, set in a cir- cular brass mounting', is fixed at the end of a short tube projecting horizontally into the room from the window shutter, and is illuminated evenly and steadily by a beam of sunlight reflected from the mirror of a heliostat outside the window. Exactly in line with the axis of the tube, and therefore with the direction of the light, a camera was mounted, armed with a Dallmeyer triplet lens. Rep- resenting the moon by a disk of black paper, my first experiment was to paste this disk directly upon the ground glass, adjust the focus for the two together, and then take an instantaneous picture. As was expected, a print from this negative showed not the slightest trace of a bright border to the line of the dark disk. I next placed the artificial moon three -inch en or so in front of the sunlit ground glass, so that its image in the camera should appear to eclipse about one-third of the ground- glass disk, then changed the focus to correspond with the altered distance of the " moon," so as to preserve the image of its edge sharp, and again exposed instantaneously. The photograph thus obtained bore an astonishingly close resemblance to a picture of the sun partially eclipsed ; so close indeed, as, at the first glance, to completely deceive Professor Ilarkness, who happened in shortly after the negative was taken, and to whom I merely showed it without comment. The ground glass being, of course, somewhat out of focus, appears most strongly illuminated in the center, with a gradual and uniform diminution of brightness toward the edges, precisely like the appearance of the sun itself, while the grain of the glass represents very well the mottling of the solar surface. But most striking of all is the riritl bonier of increased brightness adjoining the edge of the imitation moon. This appearance, identical in all respects with that shown by the eclipse pictures, is even more unmistakably marked. But to submit the question of its actual existence to a rigid test, 1 cut out a second disk of blackened photographic paper and pasted it on one of the prints over the opposite side of the artificial sun from that eclipsed, being careful that it should cover the same extent of the solar disk as the amount eclipsed by the mock moon. The print was then strongly rolled and shown independently to four different persons, who were totally ignorant of what it was intended to represent, or of what they were expected to see. Each was merely asked if he observed any difference, without a hint as to the /./<? of difference, between the two concave edges presented by the picture of the " sun." Three replied instantly and unhesitatingly, yes ; that one border was brighter than the other, all designating for the edge possessing this bright border that of the arti- ficial moon. The fourth answered equally promptly that one looked " sharper" than the other; and being asked to define what he meant by " sharper," replied that one edge appeared to standout more vividly sharp and clear cut, because the gray background iras lighter immediately along its bor tier than on the opposite x'lc. lie also, of course, pointed out the "eclipse" edge as that adjoining which the brightening occurred. To make sure that the appearance was not a chance eftect on thai particular negative, owing to some unnoticed error in the, method of conducting the experiment, I repeated the hitter on another day, taking a second negative with a flat disk for the moon, and a third with the bowl of a hemispherical porcelain capsule substituted for the disk. The effect was I lie same an increased brightness along the line of the imitation eclipse. A final test was made with one of the negatives itself, placing beneath it a piece of paper on which was a line of printed dots. Holding the negative, then, to the light the dots could be plainly seen even through the cen- ter of the image of the ground glass, but close to the concave edge of the artificial moon they dis- appeared, nor could any amount of straining of the eyes make them visible; showing that for a narrow space bordering this edge the silver deposit in the negative was actually denser than on the rest of the image of the mock sun. These artificial eclipse photographs, thus proving conclusively that the phenomenon in ques tion could be made manifest at will by photographing any opaque body seen projected against a distant luminous surface, suggested at once that the appearance ought to be one of common occur- rence in photographs, since, of course, these optical conditions are constantly present. Remember- ing, then, that 1 had indeed often seen a faint appearance of some such brightening along the edge 18* 138 REPORT OF DR. CURTIS. of opaque bodies in my photographs of microscopic objects taken through the, microscope by trans- mitted light, where, of course, the required conditions were present, I turned first to my volumes of these photographs and found, as expected, constant indications of this increased brilliancy of the field of view as the edges of opaque objects were approached. But the appearance was always faint, since in the prints the field of view itself was generally but faintly tinted. To make certain, therefore, of the actual presence of the phenomenon,! selected a negative of unusual intensity, which 1 judged should, on that account, show the brightening very strongly, and caused to be taken from it a very deep print, sodeep that in thefinished picture the main portion of the Held should be of a pretty dark shade. And the result fairly astonished me in the brilliancy and extent of the glow of light represented as bordering all the irregular outlines of the opaque object. Upon the strength of this experiment I next selected, quite at random, two ordinary stereoscopic negatives, the subject being our temporary observatory at lies Moiues as seen relieved against the bright sky, and had similar deep prints taken from them also. As confidently expected, the result was the same ; the hidden shading in the impression of the sky upon the negative was. liy the dec]* printing, forced to show itself, and the building in the center of the pictures appeared bordered by the same glow of light manifest in the photomicrographs and the eclipse photographs. And knowing how to appreciate the faint manifestation of this interesting phenomenon afforded by photographic prints of the ordi- nary intensity, I constantly find indications of its presence in photographs of every description where a dark body is shown against a distant luminous background. The phenomenon, then, so far as I know, unsuspectingly supposed, by those astronomers who have allowed it an actual existence at all, to be peculiar to a solar eclipse, is thus shown, on the con- trary, to be of invariable occurrence where the same optical conditions obtain, and to be constantly recording itself upon photographic negatives of ordinary terrestrial objects. That it is not as con- stantly noticed is not surprising, when it is remembered that the eye alone can rarely sec the phe- nomenon, since the actual increase in brilliancy of the luminous background is too slight to lie appreciated by vision in the presence of the positive brightness of the surface upon which such increase occurs. The occurrence of the brightening in photographs, also, though 1 tind it has been frequently noticed by photographers beside myself, yet does not arrest serious attention, both because, as ordinarily printed, the luminous background upon which the brightening occurs appears itself almost colorless, and because, as thus shown, the increase of brilliancy is generally more gradual and diffused than in the case of an eclipse, where there appears .almost a well -defined " baud" of bright light immediately bordering the limb of the moon. The phenomenon, in its terrestrial manifestations, therefore, can only be shown by means of a very delicate photometer, or by the sim- pler method adopted above of taking very deep photographic prints from rather under-exposed and strongly intensified negatives, which, by greatly exaggerating all contrasts of light and shade in the original object, will make plainly visible a slight increase of luminosity in the background which might otherwise escape detection. The phenomenon being thus found to be one of general occurrence, requiring as conditions only the projection of an opaque body against a distant luminous background, it was evident to me that the explanation must be sought in the general laws of optics, and diffract ion at once suggested itself as the only possible cause of the appearance. Upon analyzing, then, what would be the effect produced by diffraction where, instead of a single spherical wave of light from a radiant point fall- ing upon the diffracting body, an infinite number of such waves from an extended radiant xvrface were suffered to impinge upon it, it became at once manifest that not only miyltt the phenomenon in question be explained as an effect of diffraction, but that under the conditions named just such an appearance must occur as an inevitable consequence of optical laws. If we place in the path of a cone of diverging rays of monochromatic light, emanating practically from a single point, a solid obstruction and receive its shadow upon a screen, we have the well-known effect of diffraction the line of shadow is bordered by a stripe of increased brightness, that followed by a dark stripe. and that succeeded by another bright one, and so on, the stripes gradually fading in intensity. l!ut this point must be remembered : if we take as a mean the degree of brightness produced on the screen by the unobstructed ray, it is a consequence of optical laws that when, by the interposition of an obstruction, these alternate bright and dark stripes are produced, the positive elfect of 181)9. 139 increase of brightness above the mean in the bright stripe is always greater than the negative effect of diminution of brightness in the succeeding dark one. That is, the sum of the gain of light in all the bright stripes produced by diffraction is greater than the sum of the loss of light in the dark ones; so (hat could \ve blend the bright and dark stripes together, we should have, as the resultant of the dillVaction effect, a general increase of brilliancy upon the screen bordering the shadow of the diffract ing body, and diminishing in intensity in the direction outwards from the line of the shadow. Now this blending of the stripes is exactly what must occur when, instead of receiving light from a radiant point emitting a single diverging cone of rays, the illumination is obtained from a radiant mirfdrc, emitting of course an infinite number of such diverging pencils from points differently situated. Each of these pencils will produce its own system of stripes by impinging upon the obstruction in its path, and each of these systems will have a different locus according to the position of the individual radiant point to which each owes its origin. And there- fore, since I lie radiant points of the illuminating surface are infinitely close, the systems of stripes must be indistiiiguishably blended, and must, in accordance with the above mentioned law of dif- fraction, produce as a resultant the, effect of a general accession of light upon the screen. But now, since the light comes from an extended surface, the diffracting body has no sharp line of shadow, and the accession of light, produced by the diffraction, being distributed over the whole extent of the penumbra, cannot be demonstrated by the method of receiving the rays of light npou an extended screen. But if a lens be employed and a sharp image of the diffracting body formed in a camera, it seemed to me that the action of the lens in referring each individual ray from the radi- ant surface to the same position in the image as the position of the original point of emission in the surface itself, should confine the uppnrent diffraction effect upon the image to a comparatively narrow strip of the radiant surface adjoining the edge of the diffracting body, and thus cause to appear on the screen of the camera just such an apparent smooth increase of brilliancy to the lumin- ous background immediately adjoining the line of projection of the opaque body as lias been shown to occur in photographs both of celestial and terrestial objects taken under the above conditions. Desirous, however, that these general ideas should be critically analyzed by competent author- ity, I placed a set of the various photographs showing the phenomenon in question, together with the above hypothetical explanation of its occurrence, into the hands of Dr. F. A. P. Barnard, Pres- ident of Columbia College, Xew York. That eminent physicist, admitting at once the objective reality of the phenomenon as shown by the photographs, as indeed it is impossible not to do, was disposed to regard my explanation as the only possible one, and kindly interesting himself in the matter, undertook to study the subject critically, especially with reference to what would be tne manifestation of diffraction phenomena in case an image of the obstructing body were formed in a camera by a lens. The results of his analysis, fully confirming the hypothesis advanced as the true explanation of the phenomenon of the "brightening," Dr. Barnard has communicated to me in the following letter, which I am happy to have his permission to quote here in full: "COLUMBIA COLLEGE, NEW YOHK, " President's Room, November 2, 1869. "My I>KAI; Sn; : Pressing occupations, since I had the pleasure of seeing you here, must be my apology for not having more, promptly attended to the matter on which you desired my opinion. I feel quite satisfied that you have hit upon the correct explanation of the phenomenon to which you drew my attention, vi/: the reinforcement in a photographic picture of the lights along the margins of opaque objects relieved against a uniformly illuminated background. This effect I think to be evidently due to the same causes which, under circumstances easily realized, produce what are called diffraction fringes. To illustrate this take the following figure, in which SS' repre- sents the visible disk of the sun, M.M' that of the moon, and XY an indefinite plane. 140 REPORT OF DR. CURTIS. n QP (L3. "Drawing S M E, S' M 13, the limit of the dark shadow will be M E, and that of the penumbra M D. To any observer situated between D and E the sun will be par- tially obscured. Let Abe the obser\er's place, join A M and produce' it to P. Since every point of the sun's luminous surface may be taken as the origin of a spherical wave, and the actual luminous effect which reaches any point as A is the resultant of all these waves, we may first suppose no other luminous origin but 1' to exist. Then, as is well known, there will be formed on the plane X V, and near to A, a series of fringes alternately bright and dark, as B, B', B", &c., (these letter* being supposed to occupy the places of the bright fringes.) At A itself the illumination will be reduced to one half that which the unobstructed wave would have produced. "From A set off A C equal to A B, join (' 31 and produce it to Q. If Q be taken as the origin of a second spherical wave, it will produce a series of fringes, of which the first bright one will fall on A. Further Y on, as at E, may be taken the origin of a third wave, of which the first ~dark fringe will fall on A: then another of which the second bright one D u BBBAC JE ~ may fall on A, and so on. "If we take unity to represent the total illumination produced at A by an unobstructed wave, then the resultant effect of all the component impulses above supposed to affect that point will be positive; that is, will exceed the effect which the same number of independent waves reaching A without interference could produce. To show this, let m, m', m", &c., express the values of the abnormal excesses of light in the successive bright fringes, and , n', n", &<., the quantities of light extinguished in each of the dark fringes, n itself being the amount, suppressed at A of the light of the wave P, which, as we have seen, is one-half. Now, the values of m, m', &c., are all greater than one-half, and those of n, n', &c., are all less than one-half, except that of n itself. Hence the total illumination I at A will be expressed by the equation 1=1-1- (m n) + (m'n 1 ) + (m"n") + (m"'n'") .... in which all the terms inclosed by parentheses are positive. As the fringes diminish toward B in intensity, it is obvious that the illumination of the surface XY will similarly diminish in brightness in the same direction. And because the points taken in the sun's disk in the direction PR may be innumerable and indefinitely near together, the decrease of brightness will be uniform, and the fringes as such will disappear. The curve ab may represent this decrease. In looking upon any such extended surface exposed to the sun's light we shall, however, perceive no such inequality, because the great flood of light from the portions ot the disk too remote from P to be affected by diffraction, as for instance V, drowns out the comparatively feeble effect produced by the small number of rays which graze the moon's limb. But if a very small perforation be made in the plane XY, supposed opaque, and the rays passing through be allowed to form an inverted image of the sun and moon upon a screen behind XY, then each portion of the disk will contribute to make up only its own part of the picture, and the differences of illuminating power in the several points will become sensible. This is what the camera obscura does; for though the objective lens is not a point, yet its effect is to confine all the rays which proceed from any point of the object to t he same point of the image; and hence it will increase, by its whole optical power, the actual inequality of bright- ness produced by diffraction. "That it may appear how the unequal illumination ab on the plane XV is transferred, in the image, to the margin of the moon, join Q A, Q being the center of the wave which throws its first bright fringe on A. To an eye at A, this fringe will appear to be at F. In a similar manner other fringes would be formed at F' F", &c., by other waves. And the same causes which obliterate the boundaries of the fringes B, B', B", will also cause those of F, F', F", to disappear. "The fact that the excess of brightness between A and I." is not perceptible on the indefinite surface XY, is not owing simply to the cause above assigned for it, viz: the great light from the large portion of the sun's disk which is uncovered; but, further to the fact that the point A being arbitrarily taken, a similar effect might be argued at every other point within the penumbra between OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 141 D and E, as is illustrated for the point I", by the curve u! //. Such au effect would, therefore, be practically uniform throughout I>K, mid would not interfere with the gradually decreasing bright- ness along XY between D and E, due to the increasing obscuration of the sun in the direction Y. "But when we suppose the sun's light to be transmitted through the minute aperture A or through a lens, the excess of illumination produced by diffraction is confined to the rays which come from the points of the sun's disk directly iu line with the moon's limb, and hence their superi- ority of illuminating effect becomes manifest. "Your suggestion that the diffraction of the sun's light ought to produce sensible, fringes in the few moments just preceding total obscuration by the moon is just; and your question as to whether these may not be large enough to admit of being directly observed is one which may lie answered by computing the distances at which the successive bright fringes ought to be formed from the margin of the shadow. This may be done by means of the formula in which r is the distance from the source of light to the diffracting body; n the distance from this body to the screen on which the fringes are formed ; A the mean length of the luminous undulations, and ? the distance sought. This formula gives the distance of the first bright fringe. Those of the succeeding fringes will be obtained by multiplying the result by V3, V, -/7, &c. "Putting r + s (the sun's distance from the earth) at 92,500,000 miles; s (the moon's mean distance from the earth) at 240,000 miles, and / = ;r(T J U5 of au inch, we shall have, for the distances from the margin of the shadow of the first four fringes, Ki feet, SO feet, 103 feet, and 122 feet respectively. Though these alternations of light and shade will travel with great velocity, yet to an observer situated above the earth's surface at a moderate distance, it would seem that they might be perceptible. " In the experiment on an artificial eclipse described by you .is conducted in your chamber, the fringes must be much smaller. Taking conjecturally =! foot and s=10 feet, the value of 3 becomes one-sixth of an inch; and the series of fringes will occupy the points distant 0.10 inch, 0.28 inch, 0.36 inch, and 0.43 inch from the border of the image of the eclipsing body. "Please pardon my delay in attending to your questions, and believe me to be, "Very sincerely, yours, "F. A. P. BAKNARD. "Dr. EDWARD CURTIS, "Brevet Major United Matrx Army." The above clear exposition of the general fact that an appearance similar to the solar-eclipse phenomenon under discussion must theoretically occur wherever an image of an opaque body, viewed against.a distant evenly illuminated background, is formed by a lens, will, it is believed, when taken in conjunction with the experimental proof shown to be afforded by photographs of all descriptions, completely set at rest the question of the cause of the "bright band" seen to border the eclipsing limb of the moon during the transit of the latter over the solar disk. And with the explanation of the phenomenon as simple diffraction light, the last prop that could even be sup- posed to support the theory of the existence of an appreciable atmosphere to the moon falls to the ground.* "The question discussed by Dr. Barnard as to the size and consequent visibility of the distinct fringes that must theoretically border the shadow of the moon occurred to me from noticing that Professor Alexander, in his f/ahrador expedition to observe the eclipse of July, 1860, directed the seamen on his vessel to watch for the possible appearance of sueli fringes, and that the men reported that they did indeed sec sonic ' Hying shadows" and a " slight quivering of the last beams of the sun." (Report of the Superintendent of the United States Coast Survey for 1860, pp. SMr> and '-'(iT. ) Dr. Barnard shows that the diffract ion Cringes in question will lie litnir enough to be observed, but there must still remain as dilh'eulties in the way of the observation the tremendous velocity with which the moon's .shadow travels over the earth and a certain amount of confusion in the fringes themselves, since a slight overlapping of independent sys- tems of fringes must still persist. The difficulty of the swiftness of the llight of the moon's shadow might, to a certain extent, be avoided by observing from a point upon the exact nxtryin of the belt of totality, instead of upon its central line, since at such a station the fringes will rush past the observer in the general direction of their length instead of their breadth, and will thus be more readily detected. 142 REPORT OF DR. CURTIS. -'. Photographs of the totality. It is a matter of very great s;ilisl';i<-tii>ii tliiit, despite all the difficulties experienced on account of the Lazy weather, two such exquisite negatives of the total pliase of tLe eclipse were secured negatives that are of value not only as affording pictures per- fect in every detail of some unusually remarkable groups of solar protuberances, but also, it is believed, as marking an era in eclipse photography, proving, as they do, that by a proper selection of chemicals and with a siitliciently short exposure to the plates, the photographic art is capable of yielding pictures of the red prominences of a beauty and delicacy of detail never approached before. These negatives show that even the most massive and dense of these gaseous mountains possess many interesting points of structure, which can, and therefore in future ought to, be perfectly pre- served on the photographic plate; while they prove that it is only by a very accurate timing of the exposure that the true form and appearance of the more; delicate flame-like prominences can hope to be shown at all. Finally, they teach that, by a judicious choice of the proper photographic formula? and processes for this special work, an impression of the corona sufficiently decided to indicate its general features can be obtained with an exposure that is still not too great for any but the very brightest of the prominences, thus rendering it possible to secure in future on one plate, even during a totality of very short duration, a valuable record of all the phenomena of that phase of an eclipse. In printing from these negatives much of their detail is lost, since they stand just as they cauie from the fixing bath, having been neither redeveloped, intensified, nor retouched; and, as a consequence, the impression of the fainter portions, especially of the corona, is not what a photo- grapher would call of "printing strength." But believing that the relative intensity of the images of the various prominences and of the corona was itself a point of practical interest, I preferred not to produce any falsification by after-intensifying of the plates, but to preserve the original nega- tives as exact records of all those phenomena of totality which it is possible for photography to show. There are but two points to be regretted in connection with these negatives. One is. that the first and last few seconds of totality were lost from the exposures-, and consequently the narrow, continuous line of the main layer of the chromosphere immediately surrounding the photosphere does not appear at all in the first plate, and only as a mere trace in the second. As will be recol- lected, the first twenty seconds of totality were spent in struggling to see the all lint invisible image from the finder in order to be sure of the adjustment of the telescope, and the last nine were also lost because the calculated time for the reappearance of the sun, as given me by Professor Haf- ford, was between nine and ten seconds too early, reckoning by Professor Eastman's rendering of the actual time of the third contact. The first plate, then, according to the latter astronomer's observations, represents the appearance of the phenomena for sixty -'six seconds following the twen- tieth second of duration of totality, and the second for forty-five seconds immediately preceding the ninth second before the termination of that phase. The other slight cause for regret is that, owing to the same difficulty in seeing the image whereby to adjust the telescope for the second plate, the centering on that occasion proves to have been faulty, and the image, of the moon in the second negative is a little off' the field on one side. But since the portion so cut off' is the south- eastern limb, where at the time the negative was taken the prominences were all covered by the advancing moon, the mischance is of no consequence, except in eclipsing the image of the south- eastern position wire and marring the symmetry of the picture by the moon's lunb, as defined by the corona, being lost for a quarter of its extent. In this negative but two of the extremities of the position wires are shown, namely, the north and southwestern ones, while on the first plate all four are clearly visible. Plates X and XI are lithographic fac-similes of these two totality pictures. The drawing on the stone was done under my personal supervision, and great pains were taken that it should be in all respects an accurate copy of the originals. But it is impossible to reproduce upon stone all t In- delicate detail of these negatives, and the description that follows is intended to apply to Un- original photographs rather than to these lithographic plates. The latter represent the sun and moon in the position they assumed to the naked e\e at DCS Moines, the upper position wire being thus northeast, the right-hand one northwest, the lower southwest, and that on the left southeast. In studying the phenomena of the total phase of the eclipse these photographs are, of course, of great assistance. And though, so far as the red protuberances are concerned, the genius of OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 143 Lockyer, Janiiseu, and lluggins lias rendered it 110 longer necessary to wait for a solar eclipse in order to study their form, structure, and constitution, yet accurate photographs of the phenomena of totality are still of interest, if not value, as affording a faithful representation of the peculiar features of the corona and of the appearance at a given time of large groups of protuberances, whose mutual relations can thus be more readily recognized than by the plan of viewing the indi- vidual prominences in succession by means of the spectroscope. And such a comprehensive survey of the combined appearance of the corona and of groups of protuberances is of especial interest at this time in connection with the important subject of an outer solar atmosphere beyond the layer of the chromosphere a subject upon which the views formerly entertained have of late been necessarily greatly modified by the results of spectroscopic observations. This means of research has now quite conclusively shown that the compound gaseous atmosphere formerly imagined to extend to an im- mense distance from the surface of the sun, and to be the seat of the absorptive action producing the dark lines in the continuous spectrum of the photosphere, does not exist as supposed, but that this action takes place beneath the chromosphere. Moreover, from the known excessive tenuity of the gas in the summits of the red protuberances, and from its comparatively moderate density even in the main substance of the chromosphere,* it follows that whatever gaseous matter exists beyond this envelope must be in a state of extraordinary rarefaction. Xow difficult and perplexing though it may be to conceive of an atmosphere that will exist above a layer of extremely rarefied hydrogen gas, yet the evidence afforded by these photographs that the corona is such an atmosphere seems incontestable. In the lirst place, that this strange halo cannot belong to the moon might be considered sufficiently certain from the numerous considera- tions that render impossible Hie existence of any appreciable lunar atmosphere. But positive proof is afforded by the two photographs, which, when compared together, show unmistakably that in August last the corona -was progressively eclipsed by the ad vaneing moon precisely as were the protuberances. In the second place, the notion that the corona may be the luminosity of our own sun-lit atmosphere beyond the belt of totality is also both theoretically impossible and practically proven false by the testimony of the photographs. As to the theoretical considerations, it is suffi- cient to point out that with the diameter of the moon's shadow upon the earth twice or three times as great as the vertical extent of our own atmosphere, it is geometrically impossible for an observer near the center of that shadow to see any portions of our atmosphere which lie beyond the cone of darkness which portions alone, of course, could under the circumstances be illuminated in appa- rent contiguity with the moon's limb. This illumination of the earth's atmosphere, could it take the form of a distinct halo, resembling the corona at all, would necessarily appear as an immense ring of light in the heavens, altering its apparent relative position with respect to the moon, as the latter body advanced in its transit over the sun. Theory alone, then, would force us to the conviction that the corona must belong to the sun ; but, as previously stated, positive evidence pointing in the same direction seems to be afforded by the photographs, in the fact that they show an unmistakable relationship bctirrcn i-orona anil protuberances, the corona being markedly deficient immediately over those prominences where the substance of the chromosphere has been heaped up into apparent solid nodules, and markedly brilliant in and among the closely grouped protuberances composed of long waving tongues and small detached masses of gaseous matter.t These peculiarities of the corona were quite generally noticed by the eye-observers also at DCS Moines, where the brilliancy of the corona light was dimmed by the haze; but I can readily conceive that in a clearer atmosphere they would not be so apparent, since from the great depth of corona looked through, the total visual luminosity along a given line of sight might be so great that a considerable excess or deficiency of brilliancy for a space of but limited extent along this line might be relatively too slight to be detected upon viewing the corona as a whole. In the photograph, however, where the total effect is * Frankliiml and Lockyer. Proceedings of the Royal Society, Vol. XVII, No. 109, pp. 289, 290. t The lithographic fac-simile of the first totality picture (I'l ate X) while giving a faithful representation of the intensity and general extent of the corona, us shown by the photograph, I am sorry to find fails, in printing, to show the irregularities of its outline. The corona should appear almost alisent in a direction towards the right-hand upper corner of the plate, and should show a marked converging burst of light exactly towards the right-hand side of the picture. In and among the group of protuberances embracing Hie " T," the corona light should also appear much stronger than the lithograph represents it. Plate XI (fac-simile of the second totality photograph) is, however, very faithful in its representation of (he corona. 144 REPORT OF DR. CURTIS. but faiut, these variations iu the coronal brightness in the plane of the great circle of the solar sphere normal to the line of sight become readily manifest. Other irregularities in the features of the corona, incompatible with the notion of its being a phenomenon of our own atmosphere, are shown by the photographs, namely, a converging bundle of rays stretching out to the northwest, and, what especially points to the corona's being an envelope of the sun, a well marked deficiency of the halo in the neighborhood of the solar poles.* And still more conclusive than any of these photo- * Since writing the above, I have read with considerable surprise an extract from a letter of Dr. B. A. Gould to Professor Henry Morton, of the Franklin Institute of Philadelphia, published in t he current .October number of the journal of that institute, (page 222) in which Dr. Gould says : " An examination of the beautiful photographs made at Burlington and Ottnmwa by the sections of your party in charge of Professors Mayer and Hiiues. and a comparison of them with my sketches of the corona, have led me to the conviction that the radiance around the moon, in the pictures made during totality, is not the corona at all, but is actually the image of what Lockyer has called the chromosphere." Dr. Gould proceeds to specify the points at variance between the corona as photographed and the same object as seen and sketched b\ him, and because the two representations do not correspond in feature he infers that the objects depicted cannot be identical. This same argument would apply equally well to the ' radiance" shown in my own photo- graphs, since in them the phenomenon, though faint, agrees in outline with the' similar object on the Burlington and Ottnmwa pictures. Now I cannot but believe that Dr. Gould is in error in imagining this aureole not to be simply the image of the more intense portion of the corona near the surface of the sun. In the first place the experience of this very eclipse has shown how guardedly all sketches and drawings of the appearances of totality should be receh ed as a Hording an accurate record of either the shape, size, or position of the various objects. This is evident upon comparing the various sketches made by eye observers of the protuberances and corona, both with each other and with the photographs, and observing the very great discrepancies manifest. Of course it is not meant that accurate measurements made by a micrometer eye-piece in the telescope or similar determinations of position angle cannot be relied upon, but, on the con- trary, the argument is that only such are to be received as trustworthy, and that all yi-wraJ sketches and drawings made hastily during the few exciting minutes of totality, or from memory afterward, form but a weak ground upon which to base an important scientific hypothesis. But positive proof in the question a I issue is atlbrded by the very perfect photo- graphs of the corona taken at Shelbyville, Kentucky, by Mr. AYhipple, of the Cambridge expedition. Here we have a series of several negatives obtained by receiving the focal image of a six-inch object-glass directly upon the sensitive plate, and taken with a wide range of exposures from five to forty seconds. Of these the one exposed the longest yields a splendid and unmistakable picture of the corona, representing it. where the converging rays occurred, of a depth equal to a quarter of the moon's diameter. Surely Dr. Gould c: of imagine the aureole of thi* photograph to be the chro- mosphere and not the corona, and yet all of these pictures of Mr. Whipplc's, ami nil of the Philadelphia expedition, and my own agree perfectly in the features and position of the \ arions irregularities in the outline of the corona, the differ- ence in the representation of that object in the several photographs being solely one of extent and brilliancy. Dr. Gould adduces as an additional argument in favor of his assumption the observation that the long coronal beams, appeared to him to be "variable." while the " aureole" photographed was evidently " constant" during t he time of totality. This argument, however, loses some of its force when it is remembered thai to other observers the corona appeared to the eye absolutely unchangeable, both in form and position, during the whole period of the total obscuration. Perhaps Dr. (Jould, since he based hisbypothesis upon an examination of the photographs taken by the Philadelphia expedition, was influenced in forming the opinion he has advanced by the fact that upon these photographs the "aureole," while falling far short of the height above the moon's limb attained liy the corona, as seen by the eye, yet appears of very great brilliancy, rivaling the protuberances in that respect, and comes to almost an abrupt termination a short distance above the solar surface. Comparing, therefore, 1>riUiiiii<-// with rjrteut, Dr. Gould may have taken the disagreement in these respects between the corona as photographed and as seen, to afford an additional argument in favor of the idea that in the former case the aureole represented could not be the corona at all. lint as a fact this great and rather undue brilliancy of the corona, considering its extent, in the photographs described, is probably altogether a pho tographic effect, such prints of the Burlington andOttumwa pictures as I have seen giving every indication that the nega lives from which they were taken were strongly intensified after fixing. This Operation, practiced to give additional den- sity to weak negatives, would have, in this case, precisely the effect of increasing on the photograph the apparent brilliancy of the corona, without adding to its extent. Moreover, that this excessive photographic brilliancy of the under portion of the corona should not be taken as a proof of any physical or chemical peculiarity in the actual object is quite con- clusively proved by my own photographs, which, while showing about the same extent of corona as those pictures of the Philadelphia, party that received the least exposure, yet represent it as a very feeble luminosity, fading gradually anil imperceptibly into complete darkness, and this while the same photographs show the protuberances of great brilliancy. If this peculiarity of the Burlington and Ottumwa photographs had indeed any influence in leading Dr. Gould into the misconception into which I cannot but believe lie has fallen, the circumstance affords but another example among many that I have seen, of the necessity that a critic, before attempting to draw scientific inferences from photographic representations, should himself become something of a photographer, else hi- will be very apt to fall into this natural error of ascribing effects wholly produced in the dark-room to physical characteristics of the object portrayed. And, by B singular coincidence, evidence that Or. Gould has not a practical acquaintance with the art would seem to be afforded iu this same published letter by his total misinterpretation of another purely photographic effect, viz: the apparent encroachment of the prominences upon the disk of the moon as seen in the photographs. This curious appearance, instead of being due to " specular reflection," is wholly a dark-room phenomenon, as will be explained in the text. 1869. 145 graphic indications is the testimony of the spectroscope, which in the hands of Professor Harkness gave for the corona a continuous spectrum with no indication of the Fraunhofer lines, and in addi- tion one bright line. In view of the above adduced evidence, then, we seem warranted in considering it quite cer- tain that the corona belongs to the sun, and there appears at present no escape but to assume it to represent an extremely rarifted atmosphere above the hydrogen envelope of the chromosphere. Pending, then, the results of future researches upon this mysterious and almost impalpable gaseous atmosphere, it is well to search for such circumstantial evidence as to its existence and its physical conditions as may be afforded by the aspect of the underlying solar prominences ; for it is evident that these by their appearance should indicate whether the gaseous medium that surrounds them is of such extreme tenuity and subject to such sluggish motions only as to be practically powerless to affect by its pressure and currents their rapidly changing forms, or whether, on the other hand, this atmosphere, rare as it must be, is yet of sufficient density and the seat of sufficiently violent winds to palpably blow the light matter composing the chromosphere before it, and to be thus one of the agencies in producing the peculiar and phantastic shapes which the protuberances from the surface of this gaseous envelope frequently assume. Now in studying the aspect of the prominences, as shown by the photographs, with this object in view, it is impossible not to be struck with the fact now quite generally noticed in obser- vations of the protuberances, that these bodies are unquestionably produced at the outset by the action of forces from within or beneath the gaseous envelope of the chromosphere itself that they are upheavals, in other words, and not in any respect waves upon the gaseous sea blown into exist- ence by winds of an outer atmosphere. This appearance of upheaval is perhaps most strikingly manifest in the magnificent prominence seen at the under southwestern border of the moon, which, from its size and splendor, has been universally called the "great protuberance." On examining this in the second totality photograph, holding the plate so that the prominence shall be uppermost, it will be seen to closely resemble in character a bubbling spring, or a fountain whose discharge pipe terminates a little below the surface of the water. There is the same appear- ance of vast volumes of matter tossed up into an irregular heap by the ejecting force and sinking back again on all sides in long vertical rolls. Four such down-pouring streams of gas are visible in this fiery fountain, two of apparently greater density, because viewed directly from the front, flowing toward the observer, and the others, one to each side, leaving a clear space between their under surfaces and the main layer of the chromosphere, which, reaching right and left from the central streams, is just visible as a narrow lino above the limb of the dark moon. It would seem that in this case the upheaving force was directed obliquely to the right, (the photograph being still held upside down,) and was also advancing in the direction of its slant, since the middle streams roll down with a little inclination to the left, the right-hand one is sharply bent as if by the main mass of the protuberance pressing against it from behind, and that on the left is trailed off into a beautiful long streamer of considerable tenuity, which, finally breaking up into little detached masses, sinks down until lost behind the body of the moon, the appearance being not unlike the long trail of smoke from a locomotive. Xorth. of this great fountain protuberance is a group aptly named by some one the antelope horns, which exhibits no less markedly their formation by ejection from the gaseous stratum below. Here, ho\vevcr, the matter would seem to have been forced up in a double narrow column, of which one at least was possessed also of a spiral motion, since the north "horn" still shows a distinct spiral twist, perfectly visible in the photograph. These two columns, falling apart, are seen sinking back to the surface of the sun in opposite direc- tions. Beyond this group again, still in the second photograph, is a bright prominence strongly suggestive of the action of a sudden and, as it were, explosive force, the gas flaming out in all directions from one point of greater intensity close down to the border of the moon, the whole looking like the bursting upward of a bombshell. On the first totality plate there are visible, beside the great fountain protuberance, two others of massive character, one of them, surmounted by two short tails or streamers, bearing a rude resemblance to the head of some of the long-eared varieties of owls. The appearance of this prominence suggests the idea that it is rotating on a vertical axis. Xeither of these protuber- ances presents any striking features, so we may pass at once to the main object of interest in this 19* 146 REPORT OF DR. CURTIS. picture, namely, a group of delicate, phantastic name-like prominences, extending along the eastern limb of the sun for a distance of 35, and shown in the photograph with exquisite beauty. The most southerly of these bears a striking resemblance to a capital T, the cross-piece being entirely detached from the main shaft and curved with the concavity toward the sun. This prominence looks precisely as if it were the eifect of a sudden spirting of gas ejected directly upwards from the surface of the chromosphere, of which the top of the column, its force being spent, is rolled into a huge ring, like the rings of smoke from a locomotive, and is slowly settling back. It is very like many of those figured by Professor Zollner, as seen by him in his spectroscope.* Immediately beyond this prominence is another long, narrow wisp of gaseous matter curling to the north and ending in three detached masses, which, having apparently floated oft' from the end of the wisp, seem to be falling back to the sun. The whole suggests the appearance of a rocket just burst, when the stars and the long curved tail are both slowly sinking to the earth. Next to this rocket occurs a confused mass of rolling flames of gradually decreasing height, which look as if they too had been previously waving in long tongues, but were now bowed down and rolled into a heap together. Beyond them, in the middle of a space almost devoid of corona, stands the most inter- esting of all the protuberances seen during the eclipse. It is composed of a narrow tapering body inclined to the sun's surface at an angle of 45 toward the north, and terminating in three long, widely divergent streamers. The body tapers to the finest point, where it apparently touches the lunar disk, and contains four nodules of greater density symmetrically arranged. Of the stream- ers, one starting from the upper surface of the body as it stands inclined, passes vertically upward a short distance and then, bending sharply down almost at a right angle, sweeps off to the south. The two others, the middle and brightest one of the three being a continuation of the main body, follow the general direction of the latter toward the north while curving gradually downward. All three in their final course are very nearly parallel to each other, and would, if prolonged north- ward, meet the surface of the sun at a very acute angle. From the striking resemblance which this curious protuberance bears to an ear of Indian corn as seen growing iipon the stalk with the long points of the husks waving in the wind, I have given it that name. Beyond it are two long curved tongues of gas arching sharply to the south. Now, on viewing as a whole the extraordinary group of prominences just described, it would seem that here, in exception to the indications from the other protuberances studied, there is afforded circumstantial evidence, such as it is, of the action of a local current of some gaseous medium of sufficient density to be able to bear down the substance of the prominences before it. The current thus indicated is in the form of a gigantic whirlwind upon the surface of the chromo- sphere, with, a sweep over two hundred thousand miles in diameter around the corn-ear protuber- ance as an axis. The indications, which are numerous, striking, and concordant, are as follows: In the first place, with reference to the corn ear itself, it is difficult not to believe that this prominence as represented in the photograph is, from whatever cause, rapidly rotating, since the supposition of such a motion is by far the most natural and simple way of accounting for the fusiform shape of the body and the coexistence of the widely divergent streamers, which' have precisely the aspect of being whirled off from the main mass by the action of centrifugal force. As a cause for this axial rotation, the first conjecture would naturally be that the prominence, like all that have been already studied, is a mass of glowing gas that has been projected upward from the surface of the chromosphere, only here with unusual violence, and with an accessory screwing motion, which has imparted to the mass a rotation visible at its summit, where the force of propulsion has ceased, by the whirling off of portions of gaseous matter. This supposition, however, which would hold good were the prominence isolated upon the surface of the sun, does not account so well for the aspect of the rest of the group, of which it is the central figure, as the hypothesis that the mass owes its present form and spinning motion to its being a passive victim in the vortex of a mighty tornado. The indications of the whirlwind afforded by the other members of the group are to be found, first, in the appearance of the two long wisps of gas north of the corn ear, which unmistakably owe their form and position to the same force that is acting upon that prominence; secondly, in the aspect of the rolling masses of flame to the south, which appear to be borne down by some force whose action extends obliquely outward in a straight line from the base of the corn ear, and very nearly * Astrouomische Nacliricbten, Bd. 74, No. 1769. OBSERVATIONS OF THE ECLIPSE OP AUGUST 7, 18G9. 147 parallel to the direction of the long southerly streamer from the same. Finally, evidence is afforded by the total absence of any loose wisps of gas in the bare spot upon which the latter protuberance is reared. STow, in order to understand exactly the value. of the indications thus pointed out, let us assume a whirlwind, and deducing what would be its natural effects, observe how they correspond with the actual appearances manifest in the photograph. In the first place, .it is not unnatural to imag- ine that the violent bubbling action in the chromosphere, producing the group of flames containing the "T" and tho rocket, extended originally along the whole arc between those protuberances and the wisps beyond the corn ear. Let us then assume the generation, .in the center of this troubled mass, of a whirlwind, shallow in depth but of great lateral extent. Such a tornado would naturally catch up all the flickering tongues of gas within its grasp, suck them into its vortex, and there mold them into precisely such a tapering and whirling mass as the body of the corn ear presents. The top of this gaseous column then being finally carried above the level of the whirlwind, its outer layer would be swung off by centrifugal force into just such long trailing streamers as are actu- ally found to diverge from the summit of this prominence. Beneath the whirlwind we should expect everything not sucked into its vortex to be blown flat, and we accordingly find the surface of the chromosphere for a wide extent around the base of the corn ear absolutely level, while the flaring flames to the south are bowed down into a confused heap, where they impinge upon the under surface of the tornado. And this surface, as thus sharply defined, by the line bounding the summit of the mass of rolling flames, will, when the real position of the hidden sun on the photograph is taken into account, be found to be almost exactly tangential to the solar surface at a point a little north of the corn ear, and very nearly parallel with the upper surface of the whirlwind, whose direction is clearly indicated by means of the streamers from the above-mentioned prominence. The upper and lower surfaces of the eddy, however, converge slightly toward the north, and if we assume the limit of the tornado in that direction to be reached while its sweep is yet within the tumultuous hearings of the chromosphere, we. should again anticipate precisely the appearance actually shown in the photograph. We should expect, that is, that the loose bodies of gas near the border of the storm would be caught by the gigantic eddy, and whirling around upon its outer sur- face, would be drawn out into long, curved, trailing streamers, densest at the base where still cling- ing to the surface of the chromosphere, most tenuous at the tips where spun out into a condition of extreme rarefaction by the sweeping current. And nothing could be more perfect than the realiza- tion of these anticipated effects in the two long tongues of gas seen in the photograph north of the corn ear. The curve of their sweep is probably foreshortened by perspective, but it will be at once observed that their tips point exactly toward the tips of the two northerly streamers from the above-mentioned prominence, clearly indicating that all are borne upon the surface of the same mighty current. Here, then, we luive the case of a group of striking phenomena, and a hypothesis that seems to fully and naturally account for them all. But even if we assume upon the strength of these indications that a whirlwind actually existed as imagined, the question of what was the substance that composed the wind is still an open one. Two suppositions are possible: one, that the tornado was a current in the gaseous atmosphere of the corona, and the other that it was an eddy composed of the matter of the chromosphere itself cooled below the point of luminosity. Such an eddy might readily be accounted for as follows: We have evidence in the "T," the rocket, and the corn ear prominences that the chromosphere was in this region before the time of the eclipse, in a state of unusually violent agitation, the gases being ejected upward in vast volumes and to great heights. Such masses, after the ejecting force is spent and they become cooled by radiation, must contract and gravitate back to the surface of the parent layer in currents of considerable strength. In the present case, then, where the outpouring of the glowing hydrogen had been unusually violent and extensive, it is not unnatural to suppose that the subsequent tumultuous downrush of the cooling gas should, from local causes, have taken on an eddying motion, thus giving rise to the appearance of a whirlwind of which the main substance could not be seen because cooled below the point of luminosity, but the heart, retaining as yet its heat, remained visible as the singular corn ear pro- tuberance. Whichever supposition as to the constitution of the imaginary whirlwind may be correct, it is 148 REPORT OF DR. CURTIS. important to observe that at the limits of its supposed sweep the photographs show the luminous corona to conie to an abrupt termination, although immediately beyond, in the groups of flaring prominences adjoining, the light of this phenomenon is brighter than at any other point. This fact, which gives additional strength to the hypothesis of the existence within those limits of a violent wind, shows what would a priori be expected, that the gaseous substance of this wind was com- paratively cool. Another point of interest is that the corn ear protuberance, and therefore the vortex of the supposed whirlwind, were quite close to the sun's equator, and were also in the neigh borhood of a large sun-spot and group of bright facula>. Photographs of the sun were taken for two days succeeding the eclipse, to see if any additional sun-spots would appear whose position might have been nearer that of the corn-ear prominence; none such, however, were to be found, although a second group of facula> was brought into view, whose position on the day of the eclipse must have been coincident with that of the group of protuberances containing the "T" and the rocket. Our analysis of the appearance of the red protuberances as exhibited in the photographs, results, therefore, in the finding that at only one point is there any marked indication of these bodies being acted upon by atmospheric currents, and that here, from the fact that the supposed aerial move- ment was a local eddy occurring in the heart of an unusually tumultuous outpouring of the gas of the chromosphere, it is possible that the current should be interpreted as an eddying motion of cooled masses of this substance itself, and not of the rarefied atmosphere supposed to be represented by the corona. But, however all this may be, it is evident from the striking character of the pro- tuberances shown in the photographs that much may be learned from systematic observations of the form and manner of growth and dissolution of groups of these bodies, and it is to be hoped that, following the proposal of Zollner, those having such observations in charge will make use of photography to record the fleeting forms. This could easily be done, and photographs of interesting prominences taken at short intervals during their ephemeral existence by attaching a small camera to the spectroscope, widening the slit of the latter, and receiving upon the sensitive plate the image formed by the rays of the blue hydrogen line in the spectrum of those gaseous bodies. The question of whether during this eclipse, as on the occasion of that of I860, there were any protuberances whose light Avas of so much greater photographic than visual intensity that they would impress themselves on a negative while invisible to the eye, it is premature to attempt to answer in this place. This, with the converse question, whether any protuberances were seen which do not appear upon the photographs, must be settled by the eye-observers themselves upon an inspection of the plates. It is well, however, to give the caution that in considering the photo- graphs due allowance must be made for the facts that the exposures did not include the first twenty nor the last nine seconds of totality, and that the observatory at DCS Moines was some distance southwest of the central line of the shadow. An examination of the solar negatives taken on days previous and subsequent to the day of the eclipse fails to show any immediate connection between sun-spots and protuberances. Of all the sun-spots visible on the 4th, 7th, 8th, and 9th of August none could have been in the neigh borhood of any of the prominences visible during the eclipse, except the large spot previously men- tioned as being quite near the corn ear protuberance. There is merely the coincidence to note that all the large sun-spots visible between the 26th of July and the 9th of August, (the period over which the solar negatives extend,) were, with a single exception, on the southern hemisphere of the sun ; and that during the eclipse the majority of the protuberances, according to the photographs, were upon the same hemisphere. Here again, however, allowance must be made for the position of the post of observation south of the central line of shadow. Of faculce the solar negatives show an abundance, and prove that there must have been almost a continuous line of these objects along that portion of the circumference of a great circle of the solar sphere occupied by the protuber- ances during the total phase of the eclipse. On the question of whether there was any perceptible motion in the prominences during the three minutes of totality, the photographs, on account of the excessively long exposures that had to be given the plates, unfortunately cannot speak. The great fountain protuberance and the extreme tips of the uppermost streamers from the corn ear are the only two of these bodies depicted on both of the plates, and it can merely be said that they show no signs of any perceptible motion having taken place during the time of the total obscuration at Ues Moines. 1869. 149 A point of considerable interest and practical importance in connection with the totality pic- tures yet remains to be discussed. In the photographs obtained by l)e La Eue in I860, and by Vogel iu 18GS, there is noticeable a marked irregular rounding of the contour of all the prominences, even on the side adjoining the sun, giving them a more or less beaded and sausage-like aspect, Combined with this there is also an apparent encroachment of their under edges upon the disk of the moon, apart from the spurious effect of this nature produced by the progressive motion of the moon during the exposure of the plates in the telescope. These curious appearances have been variously commented upon from time to time; some even imagining the rounding of the under edges of the protuberances to indicate that these'bodies are all separated by a narrow space from the solar surface beneath, and that they must therefore be considered as cloud-like masses floating free in the solar atmosphere. Such a supposition, however, fails to account for the encroachment of the image of the prominences upon the lunar disk, and is totally at variance with the positive knowledge we now possess that the chromosphere forms a continuous envelope around the sun, and that the red protuberances are merely irregular upheavings of its gaseous substance, which only exceptionally become detached in any large mass from the parent layer. Being satisfied that the true explanation of the appearances described was yet to be found, I inspected my own negatives after the eclipse was over, with considerable curiosity, to see what light they would throw on the subject, and was at once struck with the totally different aspect of the prominences which they afforded from the appearance of the same objects in the above-mentioned photographs of previous eclipses. Instead of dense, structureless, shapeless patches, which, with uniformly rounded out- lines, seemed to overlap the rim of the dark moon along their entire extent, I found that even the most massive of the protuberances, the " great " protuberance, presented gradations of shade, exhibiting thus interesting details of structure, and was bounded by a very irregular outline, many feathery offshoots of gas being seen to spring from the parent mass. The encroachment upon the disk of the moon, also, instead of being manifest all along the under border of the prominences, occurred only at isolated points where the light from those objects had been evidently very intense. Moreover, there were depicted many delicate, grotesquely-shaped prominences, resembling long Hickeriug flames, and of comparatively feeble intensity, whose contorted and fantastic outlines were beautifully defined, and exhibited not a trace of the patchy, beaded appearance referred to, nor the slightest indication of encroachment upon the limb of the dark moon. From the evidence thus afforded by my negatives, which, be it remembered, were under- exposed, I was at once convinced that the peculiar appearance of the protuberances in the pictures of De La Rue and Vogel was entirely a photograph ic effect due to excessive over-exposure of the plates, combined with want of perfectly sharp photographic definition in the telescope. Now, it is a familiar fact with practical photographers, or with those who are accustomed to study photo- graphic effects critically, that the image of a brilliantly illuminated white object entering into any ordinary view or portrait, where, of course, it is over-timed in exposure, is always slightly larger upon the negative than it should be, lacks the sharp outline of the original, and has all angles and irregular surfaces unnaturally rounded. Thus, a white dress in the sunlight, a flash of light from a diamond, a crack in a board projected against a bright sky, are all exaggerated in size, and blunted in outline in a photograph. There is, in other words, in the case of very bright objects a photo- graphic irradiation upon the sensitive plate, precisely analogous, though much less in extent, to the phenomenon of irradiation in the eye. In the same way as a portion of the retina, though itself receiving no rays, will yet convey the perception of light if the part immediately adjacent be very strongly impressed, so the sensitive iodide and bromide of silver in the collodion film directly adjoining a portion that has been subjected to a prolonged exposure to a brilliant light, will itself take up the action, although iu reality receiving no part of the optical image of the bright object, and be capable under the developer of attracting to itself the falling silver.* Though convinced, as previously stated, that herein was the true explanation of the phenomena under discussion, yet to put the existence of this not generally recognized fact of " photographic irradiation" beyond a doubt, and at the same time to show that it will produce precisely those curious effects observable in over-exposed totality negatives, I made upon my return to Washing- * Since writing the above I have been informed by Mr. Le Merle, who, in the course of his photographic experience, has worked with dry plates, that this action occurs with them to a much less extent. 150 REPORT OF DR. CURTIS. ton some photographic experiments with an artificial total" eclipse, devised so as to reproduce exactly the optical conditions of the genuine phenomenon. The contrivance was as follows : In a piece of ordinary writing paper a few irregular holes were cut around the circumference of a small circle. A disk of black paper of about the same size as this circle was then pasted upon the writing paper over it, so that the cut-out spaces should in every instance seem to project directly from the edge of the black disk, in the same way as the solar prominences appear to rise directly from the moon's limb in a total eclipse. The scrap of writing paper so arranged was then pasted over tin- disk of sunlit ground glass mentioned in the description of the artificial partial eclipse experiment- There were thus a moon, represented by the disk of black paper; bright prominences, produced by the intense light from the ground glass passing unobstructed through the holes in the writing paper and appearing, of course, as in a genuine eclipse, contiguous to the " moon's" limb ; and, finally, a .corona, consisting of the feeble light that filtered through the tissue of the white paper upon which the black disk was pasted. This little " eclipse" was then photographed with the Dallmeyer triplet, an excessive exposure of several seconds being given the negative. The plate was developed with a weak developer, that the action might be slow and carefully watched. At first, of course, up cam e the mock prominences alone, the edges being clear and sharp; but as the action of the developer continued and the little patches grew densely black, it was apparent even to the naked eye that the deposit of silver was overstepping the limits of the true optical image of the prominences, and that the edges were becoming blurred and the corners rounded. Finally, the faint " corona" flashed out, defining sharply the true position of the edge of the artificial moon, and it was then found that in all cases the images of the "prominences" overlapped the edge of the ' ; moon" along their whole extent, precisely as in an over-exposed negative of a real total eclipse. A second negative was then taken with double the exposure of the first, and all these effects occurred again, even more strongly marked than before, the under edge of the shorter prominences becoming now convex instead of concave and bulging far into the lunar disk. Nothing could be more striking than the exact resemblance of these mock prominences to the beaded and sausage-like appearance which the real protuberances assume in an over-exposed negative of totality. Were any further proof necessary that these appearances are purely photographic effects, it can be found by comparing with my pictures photographs of the same eclipse taken by other parties where a relatively longer exposure was given. Such a comparison will show that in the latter pictures the rounding and blurring of the edges of the prominences and their encroachment upon the lunar disk, occur strongly marked in cases where the same prominences in my own show not the slightest trace of these appearances. Now, that the blurring and rounding upon the over-exposed genuine eclipse pictures are some- what greater than on the artificial plates described, is unquestionable, but it is probable that in the former case some of the effect must be attributed to want of perfect photographic definition in the telescopes, the instruments used being ordinary achromatic refractors, employed during totality with tliefull aperture of the object-glass. And since it is likely that telescopes of this kind will often have to be used for eclipse photography, it is important to appreciate fully the fatal effects of over-exposure upon the impression of the prominences produced by the combined action described, and to know therefore that these effects may not be merely confined to a slight blurring and enlargement of the photographic image of those bodies, but- may extend so far as to totally obliterate all detail of structure and to render the true outlines and characteristic features of the protuberances wholly unrecognizable. Having thus reviewed the photographs both of the total and partial phases, we may sum up their teachings in solar and lunar physics as follows : First. They prove that the corona cannot belong to the moon, by showing that it was pro- gressively eclipsed by the latter body in its transit over the solar disk. Second. They render it almost equally certain that the corona does belong to the sun, by exhib- iting a marked relationship between corona and protuberances, and showing what would a priori be expected in an extensive solar atmosphere, that the corona, at the time of the eclipse at least, was comparatively deficient in the neighborhood of the solar poles. Third. Considering the corona as necessarily a gaseous atmosphere, they tend to confirm the deductions from theory that the gas of its composition must be of exceedingly low specific gravity, 1869. 151 and in a state of extraordinary rarefaction, by showing that the underlying red prominences on the occasion of the eclipse exhibited traces of being acted upon by atmospheric currents only at one spot, where, from the character of the supposed current, the interpretation that this was a local eddy, originating in the chromospheric matter itself, is as probable as the aswunption that it was a whirlwind of the corona. Fourth. They show that the protuberances are, certainly in the great majority of instances, if not invariably, produced by an upheaving or ejecting force operating from within or beneath the envelope of the chromosphere. Fifth. They exhibit phenomena of which one interpretation may be that the down-rush of cooled gas following an unusually tumultuous and extensive upheaving of the matter of the chromo- sphere may take the form of an eddy or cyclone of unprecedentedly vast dimensions. Sixth. They fail to show any marked connection between sun-spots and protuberances; one stm-spot only of those visible on days preceding and following the eclipse being even in proximity to any of the prominences seen during the total obscuration. Seventh. Their evidence on the question of whether there was any appreciable motion to the protuberances during the duration of totality at Des Moines is, so far as it goes, opposed to the assumption of any such actual motion. Eighth. The evidence they aftbrd that the corona cannot belong to the moon, taken in con- junction with the experimental proof adduced that the glow of light bordering the moon's limb as projected upon the sun during the partial phase is purely an effect of diffraction, and that the encroachment of the protuberances upon the lunar disk in the photographs of totality is a pbe- . nomenon of the dark-room alone, shows that none of the varied phenomena of a solar eclipse can be assumed to afford the least evidence of the existence of an appreciable atmosphere to the moon. VII. CONCLUDING SUGGESTIONS. Since total eclipses occur so seldom in any given country that it rarely falls to the lot of a single individual to observe more than one or two, the practical lessons as to methods of observation taught by the experience of each eclipse assume considerable importance. Especially is this the case with respect to photographic observations, both because, in general, photography more than almost any other art depends for success upon the absolute perfectness of each and every step in the numerous operations required in its practice, and because, as will be the case until the use of the art shall be generally adopted at observatories, the attempt to apply it off-hand to record the varied phenomena of an eclipse must necessarily be made under the very great disadvantage of the work having to be the joint labor of an astronomer ignorant of photography, and a photographer equally unlearned in astronomy. For photography can never be learned by rote, nor practiced by rule: it is an art that requires in practice special management and adaptation to suit the peculiar features of the different objects it is called upon to picture. Its best resources can thus only be fully brought out for any special work when the operators are as thoroughly conversant with the peculiar nature and characteristics of the objects to be photographed, and the photographic capa- bilities and actual manipulation of the optical instrument to be used, as with the more familiar operations of the dark-room. In order to contribute, therefore, to this desirable general informa- tion on the subject of the various requirements of eclipse photography, all the practical hints sug- gested by our late experience will be given in detail, unimportant and frivolous though many may seem to the unprofessional reader. With respect first to the telescope: if a refractor is used it is almost needless to refer to the im- mense advantage that would be gained were the optical portion specially constructed for photography both in the matter of having the lenses corrected for violet instead of mean white light, and also of having the "secondary magnifier" constructed so as to insure a flatter field than is given by an ordinary Huyghenian eye-piece. As to whether to use any such magnifier or to receive the focal image of the object-glass directly upon the sensitive plate, the arguments in favor of the former plan are given on page 124, but it may be well here, on account of the general misapprehension of the subject by such as are not practical photographers, to say a word on the matter of photo- graphic enlargements. Now it might appear to many at first sight far the better way during totality to use the focal image alone to produce the negative, and trust to subsequent enlargement 152 REPORT OF DR. CURTIS. to render visible the hidden detail of the diminutive picture. This plan, however, if the object be <i detailed representation of the red protuberances, is a fatal mistake. In the first place it cannot be too strongly insisted upon that the secondary enlargement of an image once impressed upon a wet collodion plate can never, even under the best circumstances, rival a negative obtained by receiving at once upon the sensitive plate an equally good optical enlargement of the original image formed directly in the camera; for not only does the size of the grains of silver forming the pho- tographic image put a definite limit to the minuteness of detail that can be recorded by the negative, but it is a well-known law in photography that even- in the best copies a certain amount of the details and "half-tones" of the original picture is infallibly lost in the copying process. Secondary enlargements, then, are at best but poor substitutes for negatives of the same size obtained by direct amplification in the camera, where the character, (especially in the matter ot'JIatncsx,) the dimensions, and photographic brilliancy of the object to be depicted render this possible. Moreover it must be remembered that to produce even moderately good enlargements, such as they are, the original negative must be unusually excellent. The adjustment of the focus must be absolutely accurate, the length of exposure just right, and the chemicals exactly suited to the character of the object to be photographed, so that even the most brilliant lights may appear of very moderate density in the negative. And there must be no chance flaw in the collodion film : any accidental speck, bubble, or microscopic shred of linen or cotton falling on the plate from the air might, from the smallness of the image, totally obliterate some really large and important object. Now where there is oppor- tunity for repeated experiments, as in lunar or planetary photography, trial after trial can be made until a perfect negative fit for enlargement is obtained; but during the total phase of an eclipse, when all has to be staked upon half a dozen plates at most, and when the length of exposure even for them is necessarily to a great extent a matter of conjecture, the chances of securing a negative sufficiently good to bear enlargement well are very few indeed. From these considerations, therefore, and in view of the fact now abundantly proven that the light -of the solar prominences exerts suffi- cient chemical power to enable these bodies to be photographed of a large size at once, the plan of using the focal image alone for their representation should in my opinion be wholly abandoned. Indeed I consider the indications to be to photograph the protuberances on even a larger scale than that used by me, with a view of bringing out finer details of their structure. But to do this satis- factorily the optical part of the telescope should be corrected, chromatically, for violet light, though, from the peculiar character of the image to be depicted, no special trouble need be taken to secure flatness of field; for the protuberances, it will be remembered, form a comparatively narrow ring only, the area which they inclose the moon's disk being an absolute blank. If the focus is adjusted for this ring, therefore, and the photographic definition of the instrument is good, a beautiful picture, of the prominences of large size might be obtained with a telescope which under the same circum- stances would yield nothing but a blurred, worthless photograph of an object having any great extent of surface, such as the disk of the sun or full moon. For the delineation of the corona, the results obtained by Mr. Whipple prove that the use of the focal image alone is the only means by which a picture of that phenomenon to its full extent can be obtained during the short duration of totality. And since the object to be represented in this case is a mere uniform glow of light, without any detail, the arguments used above against this method of photographing as a means of showing the solar protuberances do not apply here. The flexure of the tube of the telescope was a thing that gave me a great deal of annoyance, and one that it seems to me could be in great part obviated. In the instrument used, if the finder was adjusted so that its axis was parallel with that of the main tube when the latter was standing vertical, this parallelism no longer held good if the telescope was swung horizontal. During the progress of the eclipse, therefore, the negatives had to be watched with great care to detect the commencement of the inevitable shifting of the image from the center of the plate, and when this was found to occur, it was necessary to suspend the exposure of plates until the finder could be readjusted. In view of this annoyance, therefore, it would be well to see that the tube of an equa- torial intended for eclipse photography possess sufficient rigidity not to bend to any appreciable amount, if, as was the case in August last, the eclipse is to extend over an interval during which the sun is rapidly changing its altitude. My plan of using a trigger to release the slotted plate making the instantaneous exposures for OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, ]869. 153 tbe partial phases, I cannot but regard as a vast improvement over De La Eue's method of having the plate held by a loop of thread, which is burnt off by a lighted taper when it is desired to make the. exposure. That the trigger arrangement is quicker to set and less troublesome to work with, are perhaps minor advantages, but that its use admits of so much greater accuracy in the timing of the exposures is certainly a very important consideration. Indeed, the method I employed left nothing to be desired in the matter of accuracy in noting the exact instant of exposure. My plan was, with eye and ear upon the chronometer, and thumb resting lightly against the under surface of the projecting portion of the wooden slider carrying the apparatus for the exposures, to tap gently on the trigger with my forefinger synchronously with the chronometer beats for several seconds before exposing, so as to get the rhythm of the time-piece Avell fixed in my mind, and theii at a predetermined even second, by a slight increase in the strength of the tap upon the trigger, to release the slotted plate and effect the exposure. And such was the accuracy obtainable by this method that my ear, though delicate enough to readily appreciate the interval, minute as it was, between the click of the trigger itself and the click of the slotted plate striking home at the end of its short course, was yet unable to detect the slightest want of synchronism between the click of the trigger and the beat of the chronometer. The only possible argument against the use of the trigger, that it involves touching the telescope and so risks jarring the same, is entirely specious, for the exposure, being practically instantaneous, is necessarily of shorter duration than the quickest jar that can be communicated to the instrument. It is, therefore, really impossible to produce any blurring or doubling of the photographic image even by quite rough handling of the trigger, a fact that I took care to prove by actual trial. This method of timing the exposures I therefore consider as far the best that can be adopted. The employment of a chronograph was at one time thought of, but a very little reflection showed that such an instrument would, under the circumstances, be worse than useless ; for to have even a theoretical advantage over the method of timing described above, it would be necessary to have the seconds registered automatically, a requirement that, to be carried out in the field, would involve the construction and care of special and troublesome apparatus. And even then the advantage of the chronograph would be more specious than real, for in the method of springing a trigger synchronously with a chronometer beat, the probable error in timing the tap is actually less than the probable error of the correction of the chronometer, whose reading must in any method serve as the basis for calculating the actual instant of exposure. And icithout an automatic registration of the seconds, the use of a chronograph would evidently be only a clumsy, troublesome, and round- about way of doing precisely what is effected by my simple plan ; that is, instead of making the exposure directly by tapping a trigger synchronously with the beat of a chronometer, the chrono- graph would require that the seconds should be registered on the instrument in precisely this way by one operator, while the exposure of the plate, made by another operator, recorded itself. This chronographic method of timing would thus depend, after all, for its exactness upon the accuracy with which a tap can be made with the finger synchronous with the beat of a chronometer. It is therefore infinitely the simpler and better plan to have this tap make the exposure itself, and thus avoid both the disadvantage of the transportation and care of an additional and complicated piece of apparatus that is extremely liable to get out of order, and the very serious drawback of the necessity of an additional trained operator to attend exclusively to the marking of the seconds by the face of the chronometer. In the construction of the camera -box for my telescope a mistake was committed that could not be foreseen at the time, but which, having proved a source of annoyance on the day of the eclipse by reason of the hazy sky, should in future be avoided. This was that the wooden slider carrying the apparatus for the exposures was placed too far from the eye-piece. The effect of this position of the slider was that instead of ordinarily using, as I had anticipated, the slit in the instantaneous plate about one-twentieth of an inch in width, I found that for the sun at the altitude it would occupy during the eclipse, the whole width of the slot half an inch which had been provided to meet the emergency of unfavorable weather, was necessary even with a clear sky, if the usual two- inch diaphragm cap was used over the object-glass. Still, from the uniform clear atmosphere that prevailed at Des Moiues. I anticipated no trouble from this source, not appreciating how very much a ha/.e would cut down the chemical intensity of the sunlight, and therefore imagining that a three 20* 154 REPORT OF DR. CURTIS. aud four incli diaphragm cap, by using which four times the usual amount of light could be obtained, afforded an ample resource against the contingency of bad weather. This calculation, however, experience showed to be a mistake; and thus, when the haze on the critical day reduced the sun's actinic force, as the eclipse advanced and the sun sank lower in the west, to a tenth and a twentieth part only of the usual amount, there was no means of allowing in the exposures for this excessive diminution in the chemical power of the light, but by the very objectionable method of using the full aperture of the object-glass ; objectionable, because, as previously mentioned, the photographic definition of the telescope fell off very considerably in sharpness when more than three or four inches aperture was allowed to the object-glass. Since, therefore, experience shows that the sun can be photographed through a haze that will diminish its actinic force to a small fraction of that exhibited when the sky is clear, it is important to see that the arrangement of the instantaneous plate shall allow of an increase of exposure to thirty or forty limes the amount found necessary under the circumstances of a clear sky. Another point in the arrangement of the telescope from which an unexpected, and, in this case, very serious 'difficulty was experienced was the plan I had adopted for viewing the image from the finder by allowing it to fall upon a screen of white cardboard. This plan, which I had con- sidered the best that could be adopted, because it allowed the operator at the telescope to see the image from the finder while handling the screws that adjusted the instrument for right ascension and declination, should yet neA*er be trusted again for use during totality, my experience having shown that the image of the corona may readily be rendered so faint by the passage of its rays through a hazy atmosphere as to be totally invisible when viewed in this way. In attempting to improve upon this plan, however, the idea of having the image from the finder visible to the operator who adjusts the telescope should still be carried out; since it is impossible to adjust rapidly where one person observes the image and another handles the screws. I would therefore suggest that the finder be mounted well up on the tube of the telescope, and the image received upon a screen of ground glass, which shall then be in such a position that the operator can view the image by looking through and not tipon the screen, when standing so as to command the adjust- ing screws of the telescope. And care should be taken that the lantern -to light the face of the chronometer during totality shall not shine upon this screen. To provide against the excessive brilliancy of the image of the sun itself during the partial phases, colored glasses would have to be interposed somewhere in the path of the solar ray ; or, better still, perhaps, a flap of paper sub- stituted for the ground glass, through which the daz/ling image of the sun would not appear too bright. In the important matter of the proper length of exposure to be given the plates during totality for the purpose of showing the detail of the red protuberances, it is greatly to be regretted that though my negatives are so satisfactory in this respect, yet on account of the exceptional condition of the atmosphere through which they were taken, the exposures actually given cannot be relied upon as a basis for calculation in the future. For the sake, however, of an approximate idea upon the subject, the following analysis of the exposures is given for what it is worth. In the first place it must be remembered that the negatives, despite their present beautiful appearance, were really considerably under-exposed, the impression of the faint flame-like prominences, and of the corona, being only brought out by a dangerous forcing of the development ; that operation having been pushed, as the plates show, to the very verge of fogging. Mr. Le Merle, who managed the devel- opment, estimated at the time, and still maintains, that the, proper exposure would have been twice that actually given ; and it is probable he is right, for with a fuller exposure and a quick develop- ment the contrast between the intensity of the massive protuberances and that of the fainter and more delicate forms would not have been so violent. Starting, then, with double the exposure actually given the first totality negative as the proper time it should have had under the circum- stances that is, two minutes and twelve seconds we know, from the aperture of the object-glass used in photographing the sun during the partial phase immediately before totality, that the effect of the haze at that time was to require an increase of all exposures to an amount at the very least ten times as great as the proper allowance for a fair day. But from the fact that the partial phase negatives, even with the exposure given, are thin and weak, it is probable that the absorptive action of the haze should be taken as considerably greater, even double, the above estimate. We thus OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 155 obtain for the exposure that the totality plates should have received, had the sky been clear, a range of from six and a half to thirteen seconds, the first number probably being nearest the truth. These figures, however, it is all-important to remember, are correct only for an eclipse occurring at the same time of year, and hour of day, as that of last August ; for a station agreeing pretty closely in latitude and climate with the city of Des Moines ; for a telescope corresponding in dimension and optical arrangement with the Annapolis equatorial ; for a photographic image of the same size as that borne upon my negatives ; and last, but not least, for the same bath and collodion as those used by Mr. Ward in the dark-room of our observatory. Now, in view of the great number of considerations thus detailed as bearing upon the question of length of exposure, it is very desirable to determine accurately what Do La Eue attempted to estimate, namely, the comparative photographic intensity of the light from the solar prominences and full moon. For when this is accomplished, the would-be eclipse photographer can calculate very closely the proper totality exposure for a special eclipse, station, telescope, and chemicals, by transporting telescope and chemicals to the station in time to photograph on the spot the last full moon before the eclipse, being careful to take the moon at as nearly as possible* the same altitude that the sun is to occupy during totality. On this question of the relative chemical intensity of these two kinds of light, it is again unfortunate that our experience cannot speak decisively, since the proper exposure for us, both for the prominences during the eclipse and for the full moon, is a matter of so much uncertainty. But such as it is, the result is as follows: The probable correct exposure for the prominences, in the case of a clear sky, we have found to be six and a half seconds; and the probable correct exposure for the full moon at the same altitude my preliminary experiments showed to be twenty minutes. These figures would give as the relative chemical intensity of the light of the solar prominences and the full moon, the ratio of 184 to 1, a proportion almost identical with that deduced by De La Eue from his experiments. The corroborative evidence thus adduced points strongly to the accuracy of that astronomer's estimate, and it is therefore safe to say that the plan of experiment- ing upon the full moon, and then calculating the totality exposure according to the above ratio, is probably the most reliable way of attacking the question. But still, the first exposure during totality must .be to a great degree conjectural ; and the timing of the subsequent plates must be regulated by the result of development of the first. The operator at the developing tank has thus the vitally-important duty to perform of estimating quickly, but coolly and accurately, from the manner in which the image " comes up," what modi- fication should be made in the exposure for the succeeding plates. It is needless to say, therefore, that this post, the most responsible of all during totality, should be intrusted only to a most accomplished photographer, who understands thoroughly the nature of the object pliotographed, and the exact effect which it is desired to produce. And in future this operator will find a valuable auxiliary guide to a correct estimation of the proper exposure, in those peculiar eifects on the impression of the prominences which I have pointed out as due to over-exposure. (See page 149.) That is, if on developing a totality negative the prominences come up with their base markedly convex towards the body of the sun, there is no necessity of waiting for the completion of the development, and a careful inspection of the amount of detail obtained ; but the operator at the telescope may be at once notified that the exposure must be reduced. By this means time can be saved an all-important consideration during the few precious minutes of totality. As to the proper exposure for the corona, my negatives of course are silent, since this object is but very faintly impressed upon them ; but it may not be amiss to state that a most accurate basis for calculation on this subject is afforded by the splendid photographs of the corona already alluded to as obtained by Mr. Whipplc, at Shelbyville, Kentucky. The best of these which shows the corona very nearly if not quite as extensive and brilliant as it appeared to the eye we learn was exposed for forty seconds ; the focal image of a six-inch object-glass being received directly upon the sensitive plate. Mr. Whipple also writes :* " The day was splendid ; not a cloud to be seen." But allowance should still be made in a calculation upon this exposure for the low altitude of the sun at Shelbyville at the time of totality. With respect to the nature of the photographic chemicals best suited for negatives of the phe- * Philadelphia Photographer, September, 1869, page 291. 156 REPORT OF DR. CURTIS. noiuena of totality, the bountiful results obtained by us speak loudly in favor of the formula- em- ployed, and prove the correctness of our reasoning that for this peculiar subject a well-bromized collodion yielding soft thin negatives full of detail, is infinitely superior to one giving the brilliant dense negatives abounding in striking contrasts, which so many photographers are accustomed to use. It may also be added that since, as a general rule, the difficulty in exposing for the solar prom- inences is not to get a long enough, but a sufficiently short exposure, the supposed necessity for a neutral bath in order to obtain the greatest possible sensitiveness, does not exist ; and it is better, therefore, to use the ordinary acid bath than incur the danger of fogging, which is always to be apprehended when the neutral silver solution is employed. In the matter of the arrangement of the dark-room and apportionment of labor during the eclipse, I can suggest no improvement. The trough of water to hold the negative baths we found absolutely indispensable on account of the excessive heat of the dark room on sunny afternoons. Without the troughs the temperature of the baths was found to rise as high as 83 Fahrenheit, with fogging of the plates as an inevitable result. The plan of having the reservoir of water outside the building borrowed from De La Hue proved a great convenience in the matter of keeping the barrel filled ; and the large fixiug-trough and dumb-waiters for passing the plateholders in and out were not only conveniences, but really did the part of two additional operators. The division of labor among the four of us on the occasion of the eclipse itself, was so even that the operations per- formed by each took almost exactly the same amount of time, so that we were enabled to all work together and accomplish the greatest amount of work in the shortest possible time. In conclusion, to serve as some guide to future expeditions of this kind, I have thought it well to give a list (see Schedule C) of the articles taken by us as our photographic equipment, with the remark that of the extensive and somewhat heterogeneous assortment of materials and implements there given, there, was scarcely a thing that did not come into play. The list was made thus com plete, in the first place, because at the time of our starting on the expedition we thought it likely that we might take our station at Mitchellville instead of Des Moines; and the former being a very small country village, I considered it necessary to go thoroughly equipped in every particular, even to the being prepared to build the observatory with our own hands and tools. I am, General, -very respectfully, your obedient servant, EDWA14D OUKTIS, Assistant Surgeon and Brevet Major U. 8. Army. Brevet Major General J. K. BARNES, Surgeon General United States Army. OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. SCHEDULE A.i:;ii'il of .Yr;/(fJi><. 157 Date. Designat'u of neg- ative. rr ^ X , V ft 5* pi H Instant of expos- ure by local mean time p.m. Diameter of aper- ture of object glass used. Widthofslitinin- stantau'us slide used. Remarks. 1889. /I. HI. . /I. HI. a. in. I'H. July 26 A 11 3 25 4 46 7.9 2i A Chronometer fast 6 1 ' 17 m 17 s . 1. 28 B 11 14 55 4 57 37.5 2| ft Chronometer fast 6 h 17 m 17 s . 5. 29 C 8 49 55 2 32 38. 4 2 4 Chronometer fast 6 1 ' 17 m 16 s . 6. 30 D 8 52 15 2 34 59. 1 2| I Chronometer fast 6 h 17 m 15.9. 31 E 10 37 30 4 20 13.5 3 A Chronometer fast 6 h 17 m 16'. 5. August 2 F 12 G 55 5 49 38.6 4 i Chronometer fast 6 h 17 m 16 s . 4. 3 G 10 1 45 3 44 29. 5 2 i Chronometer fast 6 h 17<" 15 s . 5. 4 H 7 41 15 1 23 59.6 2i i Chronometer fast 6 h 17 15". 4. 7 I 8 59 45 2 42 29. 3 n Iti Chrono-jieter fast 6 h 17 m 16". 0. 1 9 59 57 3 42 41. 6 i 8 10 14 3 42 58. 6 1 3 10 46 3 43 30. 6 i First plate showing contact. 4 10 1 7 3 43 51.0 6 . 4 5 10 1 23 3 44 7.0 6 1 6 10 1 40 3 44 24. 6 i 7 10 1 54 3 44 38.0 6 i 8 10 (i 15 3 48 59. 6 i 9 It) 7 15 3 49 59. 6 i 10 10 8 15 3 50 59. 6 * 11 10 9 15 3 51 59.0 6 }' 12 10 10 15 3 52 59. 6 J 13 10 11 15 3 53 59. 6 4 14 10 12 20 3 55 4. 6 4 15 10 13 20 3 56 4.0 6 4 16 10 14 15 3 56 59. 6 4 17 10 15 15 3 57 59. 6 4 18 10 16 15 3 58 59. 6 i 19 10 17 15 :i 59 59. 6 4 20 10 18 15 4 59. 6 1 21 10 19 15 4 1 59.0 6 4 22 10 20 25 4 3 9.0 6 i 23 10 21 15 4 3 59. 6 4 24 10 22 15 4 4 59. 6 i 25 10 23 15 4 5 59. 6 1 26 10 24 15 4 6 59. 6 i 27 10 25 20 4 8 4.0 6 | 28 29 10 26 15 10 37 20 4 8 59. 4 10 4.0 6 6 } | Large sun-spot on southwestern portion of SHU'S disk bisected by moon's limb. 30 10 28 15 4 10 59. 6 i 31 10 29 15 4 11 59.0 6 i 32 10 30 15 4 12 59. 6 | 33 10 31 15 4 13 59.0 6 i 34 10 32 15 4 14 59.0 6 i 35 10 33 15 4 15 59. 6 1 36 10 34 15 4 16 59. 6 A 158 REPORT OF DR. CURTIS. SCHEDULE A.Scconl o/Ai#r<- Continued. Date. tt> 9 a Is I 1 8 3 M c X K-. <u & = fe. 4- ' S LC s ss i-H Instant of expos- ure by local mean time p. in. Diameter of aper- ture of object glass used. Width of slit inin- stantan'us slide used. Remarks. 1869. /I. JM. . 7l. Ml. *. in. in. August 7 37 10 35 15 4 17 59.0 6 i 38 10 36 15 4 18 59. 6 4 38 10 37 15 4 19 59. 6 i 40 10 38 15 4 20 59. 74 i 41 10 39 15 4 21 59.0 74 i 42 10 40 15 4 22 59. 7f i 43 10 41 15 4 23 59. 74 i 44 10 42 15 4 24 59.0 7f a 45 10 43 15 4 25 59. 74 4 46 10 44 15 4 26 59. 74 i 47 10 45 15 4 27 59. 74 4 48 10 46 15 4 28 59. 7} 4 49 10 47 25 4 30 9.0 7f 4 50 10 48 20 4 31 4.0 7i '4 51 10 49 15 4 31 59.0 7* 4 5-2 . . . 74 4 Trigger liunj; tire; time not noted. 53 10 51 15 4 33 59.0 7f i 54 10 52 15 4 34 59.0 74 4 55 10 53 15 4 35 59. 74 4 56 10 54 20 4 37 4. 74 A 57 10 55 15 4 37 59. 74 4 58 10 56 15 4 38 59. 7f 4 59 10 57 15 4 39 59. 7f n 60 10 58 15 4 40 59. 7* | 61 10 59 20 4 42 4.0 74 4 . (11 3 4 4 45 48. 0^) 03 to to 7J Totality. Exposed (K5 seconds. 111 4 10 4 46 54. oj fll 4 47 4 47 31.0^1 63 to to 7J Totality. Exposed 45 seconds. 111 5 32 4 48 16. OJ 64 11 6 5 4 48 49. 74 . i <>5 11 7 20 4 50 4. 7f . 4 06 11 8 35 4 51 19. 74 4 67 11 9 15 4 51 59. 7f 4 68 11 10 15 4 52 59. 74 4 69 11 11 15 4 53 59. 7* 4 70 11 12 20 4 55 4. 74 } 71 11 13 15 4 55 59. 74 } 72 11 14 15 4 56 59. 74 Y 73 11 15 25 4 58 9.0 74 4 74 11 16 15 4 58 59. 74 i , 75 11 17 25 5 9.0 . 7f 4 76 11 18 20 5 14.0 74 4 [port inn of sun's disk. 77 11 19 35 5 2 19. 7J 4 Reappearance of large sun-spot on southwestern 78 11 20 15 5 2 59. 7J 4 Trigger hung lire slightly ; timing not accurate. OBSERVATIONS OP THE ECLIPSE OF AUGUST 7, 1869. 159 SCHEDULE A. Record of Xeyatiees Continued. Date. if a ?l a tc 1 i! ^ tC a v _i2 h-H a . -H -*3 ~- fl O 3 C3 ^ Qj a " " M Diarneterof aper- ture of object glass used. AVidthofslitinin- stantan'us slide used. Remarks. 1869. /I. III. S. It. ill. S. i in. August 7 79 11 21 15 5 3 59. 7} i 80 11 22 20 5 5 4. 71 1 81 11 23 15 5 5 59.0 71 1 82 11 24 15 5 6 59.0 7J 1 83 11 25 15 5 7 59.0 7f 4 84 11 26 25 5 9 9.0 71 i 85 11 27 15 5 9 59.0 71 i . 86 11 28 25 5 11 9.0 71 | 87 11 29 15 5 11 59.0 71 i 88 11 30 15 5 12 59. 71 4 89 11 31 15 5 13 59. 7J i 90 11 32 20 5 15 4.0 71 91 11 33 15 5 15 59.0 71 4 92 11 34 15 5 16 59. 71 i 93 11 37 15 5 19 59. 71 j 94 11 38 20 5 21 4. 71 4 95 11 39 20 5 22 4. 71 4 96 11 40 15 5 22 59. 71 j 97 11 41 15 5 23 59. 71 i 98 11 42 15 5 24 59. 71 4 99 11 43 15 5 25 59. 7J + 100 11 44 15 5 26 59. 71 1 101 11 45 15 5 27 59. 71 I 102 11 46 15 5 28 59. 7* i 103 11 47 15 5 29 59. 71 i Fogged and spoiled.* 104 11 48 15 5 30 59.0 71 i 105 11 49 15 5 31 59. 71 4 106 11 50 40 5 33 24. 71 i Fogged and spoiled.* 107 11 51 15 5 33 59. 7J 1 108 11 52 15 5 34 59. 71 4 109 11 53 15 5 35 59.0 7} I 110 11 54 20 5 37 4. 7} ^ 111 11 55 15 5 37 59. 71 1 112 11 56 15 5 38 59. 71 4 Fogged and spoiled.* 113 11 57 15 5 39 59. 7J 1 2 114 11 58 15 5 40 59. 71 4 Reappearance of large sun-spot on eastern por- 115 11 59 5 41 44.0 7f 4 tion of sun's disk. 116 12 1 15 5 43 59. 71 4 117 12 1 28 5 44 12. 71 4 . 118 12 1 42 5 44 26. 71 4 119 12 1 58 5 44 42.0 71 J, 120 12 2 17 5 45 1. 71 4 Last plate showing contact. 121 12 2 43 5 45 27. 71 4 122 12 3 16 5 46 0. 7J 4 August 8 K 9 34 30 3 17 13.6 2 i Chronometer fast 6 1 ' 17 16M. 9 L 8 K) :,:, 1 53 38.4 2 4 Chronometer fast 6 h 17 m 16 S .C. *Fog#iDg due to a batch f cleaned plati-slwin^ s>t on a pad of lilottiinj. (i:t]M-r that was accidentally damp. As soon as the cause of the difficulty was discovered thin batch was discarded. 160 REPORT OP DR. CURTIS. SCHEDULE B. Table showing the relative actinic force of the sun at different altitudes, as determined by comparing shades of blackening of photographic paper produced by exposure to direct sunlight at different times of day for a series of definite intervals of time ranging from half a second to ten minutes.* , ' 4> r - <" ji (< a <0 <H <U ' c^ a) C s J3 ^ ~" ~ - *" "S ** * a * d PfRjt - ? W !- o o 'fl X t-t 9 A fi "3 = "8 ^ - r" no *> S 111* |J Date. Commencement lire. Local me Greatest duratioi lire of shade n comparison. Number of shade by different used in the co: Relative actinic i sunlight comp that exhibited noon of each standard. Altitude of the i time of comme exposure, give nearest degree. Keniarks. 1869. /I. HI. Ml. 8. o ' July 27 12 . . 1.000 67 Standard. Sky hazy. 2 45 p. m. 1 35 4 .105 49 Very hazy ; sun scarcely cast a shadn\v. 28 7 54a.m. 1 6 .568 31 8 54 1 15 .786 42 10 23 30 11 1.333 58 12 4p.m. - 1.000 07 Standard. 1 50 1 18 1.000 58 3 1 1 18 1.000 40 4 11 1 15 .786 34 5 6 50 8 .480 23 1 35 7 .096 13 29 5 13 a.m. 10 8 .035 2 30 5 28 8 20 9 .095 5 5 43 3 20 6 .145 7 30 5 58 1 5 .163 10 16 40 7 .263 15 6 28 40 9 .424 16 6 43 25 7 .433 18 30 6 58 50 9 .499 21 7 13 1 10 .568 24 7 28 50 10 .636 27 7 43 1 15 1.000 30 7 58 1 15 1.000 33 8 13 1 15 1.000 35 30 8 28 1 15 1.000 38 8 43 1 15. 1.000 41 9 13 1 15 1.000 46 30 9 45 1 15 1.000 52 30 10 16 1 15 1.000 57 30 11 1 15 1.000 03 12 . . 1.000 67 Standard. 1 3p.m. 1 15 1.000 04 2 1 15 1.000 56 30 3 1 9 .732 46 30 4 1 1 10 .677 34 30 4 13 1 10 .615 33 4 28 1 9 .518 30 4 43 1 10 .493 27 30 ' For an explanation. of the method by which these observations \\civ ni;nlt-. see page 130. OBSERVATIONS OP THE ECLIPSE OF AUGUST 7, 1869. 161 SCHEDULE B. Continued. I S S "35 g e S "o Jj 2 " v JH ?H ii pH 3 3 3 -B ^ S CS +s S .S '- S .2 o 3 J v P* a 1 1 3 J. " S OS a 2 PN M 9 X ^ "S S c3 " So a a V Q "~ <U 9 '^ ^ ^ .rt * <u * Date. "S ^ P jh* 3 2 2 2 a ^ ~ g s =5 s 3 * . <u - * Remarks. II 'J 'Sis -g S < "g JJ S aTiS '*- * a M *= Vt c3 p. -1 -H ^ bC * 4- i^ Q I 3 00 u O *" li! > . 'S , OJ 5 ^ Ifill $ i & I S .3 a v ^ '-*3 a O 25 's. w ^ 1869. /l. l. Ml. Jf. ' 4 58 1 10 .447 24 5 13 1 9 .342 21 30 5 28 2 30 10 .277 19 5 43 4 20 11 .164 16 5 58 4 20 9 .160 13 C 13 5 30 8 .081 10 30 6 28 8 20 7 .046 a 6 43 10 6 .022 5 6 57 5 30 1 .006 3 Taken during the setting of the sun. 30 9 Oa.m. 1 15 . 1.000 44 10 2 1 15 1.000 55 11 1 15 1.000 63 12 . 1.000 67 Standard. 3 8 p. m. 1 15 1.000 45 4 1 15 1.000 35 5 2 40 6 .313 23 6 4 20 7 .185 13 31 9 -8 a. m. 1 13 .808 45 10 21 1 15 1.000 58 11 9 1 15 1.000 64 12 . 1.000 67 2 7 p. m. 1 15 1.000 55 3 9 1 13 .808 45 5 1 50 6 .211 23 30 5 50 1 20 2 .055 15 August 2 1 2 p. m. - 1.000 63 Standard. 3 5 1 10 .714 45 3 59 1 12 .726 35 4 57 1 9 .364 24 5 59 4 20 5 .091 12 30 3 3 9 p. m. . . 1.000 44 Standard. 3 54 1 10 .730 35 5 1 1 10 .470 23 5 48 4 20 10 .178 14 4 9 2 a. m. 1 15 1.000 44 11 . . 1.000 62 Standard. 11 57 1 13 .808 66 Slightly hazy. 2 3 p. m. 1 10 .676 55 3 21 1 9 .612 42 4 43 1 8 .426 26 30 , 5 40 4 20 7 .159 16 Clondy at intervals during exposure. 21" 162 REPOET OF DR. CURTIS. SCHEDULE C. List of articles forming the equipment of the photographic I. CHEMICALS. Ammonia , . 8 ounces. Acetic acid 8 pounds. Alcohol, Atwood's 2 gallons. Bichloride of mercury 2 ounces. Bichromate of potassa 3 pounds. Bromide of cadmium 3 ounces. Cyanide of potassium 1 pound. Caustic potassa 8 ounces. Carbonate of soda 1 pound. Distilled water* 5 gallons. Ether 3 quarts. Hyposulphite of soda 15 pounds. Iodine Iodide of ammonium ' Iodide of cadmium Iodide of potassium Negative varnish Nitric acid Nitrate of silver (recrystallized) . Paraffine Permanganate of potassa Pyroxyline Sulphate of iron Sulphuric acid 12 4 1 ounce. 2 ounces. 2 ounces. 4 ounces. ounces, ounces. 3 pounds. 1 pound. 1 ounce. 4 ounces. 4 pounds. 3 pounds. II. PHOTOGRAPHIC INSTRUMENTS, MATERIAL, AND APPLIANCES. Actinometers. Balance and weights. Bottles, assorted. Beakers. Capsule tongs. Chamois skin. Corks, assorted. Corkscrew. Cork-squeezer. Crocks for cleaning solution for plates. Dipping-rods. Dumb-waiters for wall of dark-room. Dusting-brushes for negatives. Evaporating dishes. Filtering paper. Filtering stands. Funnels. Graduates. Ground glass for camera screens. Glass plates for solar negatives. Glass plates for stereoscopic negatives. Hard rubber photographic trays. Magnesium ribbon. Mortar and pestle. Photographic paper. Photographic ware baths for negatives. Precipitating glasses. Betort stands. Backs for negatives. Spirit lamps. Stereoscopic camera and stand. Stereoscopic and other lenses. Test paper. Beeswax. Black velvet. Candles. Candle-sticks. Carpenter's and other tools. Coal oil. Cardboard. Cotton-wool. Cotton-flannel. Copper still, 1 gallon capacity. Glue. Glue-pot. Glazier's diamond. Hinges, springs, and latches, for doors. Lamps. Lamp oil. Lanterns. Listing. Mathematical instruments. Matches. Mucilage. Muslin. Naphtha stove and naphtha. Nails, screws, and tacks, assorted. III. MISCELLANEOUS. Paper black, blotting, tissue, yellow. Photographic books. Pulleys and staples for hauling canvas roof. Pins. Perforated tin for guarding delivery and waste- pipes. Rope. Eubber bauds. Eubber cloth. Eubber tubing for water and waste-pipes. Sail-maker's thread, needles, and palm. Sheet tin. Soap. Sealing-wax. Sponges. Spigots. Stationery. Tent-flies for roof. Tape. Tape-line. Towels. Twine. Wax tapers. Writing diamond. Oil-can and machine oil. Buckets for carrying water, a wash-tub to make a sink of, and other bulky and common articles, were procured at Des Moines. * In addition a small still was taken, which was kept constantly in operation during our stay at Des Moines. REPORT MR. J. HO I EH LANE. REPORT OF MR. J. HOMER LANE. . WASHINGTON, D. C., Augwt 28, 1869. SIR: Having beeu attached to the party of Professor J. E. Hilgard, of the United States Coast Survey, for observing the recent eclipse of the sun, I am directed by him, in conformity with an arrangement approved by Professor Xewcomb, of the United States Naval Observatory, to report to you, in part, such observations as I made on that occasion. At the request of Professor Hilgard I joined his party, and proceeded to the city of Des Moines, in the State of Iowa, to meet him and the other members of his party there. I was expected to note the times of the first and fourth contacts of the moon's limb with the sun's limb. These observations were taken accordingly, and have been duly reported to Professor Hilgard. The times of second and third contacts were left to my own discretion, conditioned on their non- interference with the phenomena of totality. I therefore did not attempt them. Beyond the observation of the times of first and fourth contacts it was understood that my attentiou should be primarily given to the corona, but the particular point or points of inquiry were left mostly to my own discretion. As various physical considerations which have been pre- sented in published papers of Professor Helmholtz and Professor Newcomb, and in a paper of my own not yet published, but in part presented to the National Academy at its late session in Wash- ington, have left upon myself, as well as both the individuals just named, a strong impression of the extreme difficulty of realizing the existence above the sun's photosphere of an atmosphere in the ordinary sense of that term, having such a height as fifty or a hundred thousand miles, I proposed to make it the chief object of my own observation to watch for any indication that could bear on that question. More particularly I charged myself with the duty of watching for any possible very low atmospheric limit, marked by anything like a regular boundary and superior intensity of light very near the sun's limb. According to the original intention, I was to have used a Coast Survey reconnoitering tele- scope of only three inches clear aperture; but after my arrival in Des Moiues, which was not till 12 or 1 o'clock of the Thursday night immediately preceding the eclipse, Professor Newcomb, who, on the part of the Naval Observatory, had charge of the court-house square observatory in Des Moines, proposed to Professor Hilgard that I should observe with one of the much larger instru- ments which he had fitted up. One of these remained unappropriated, and was accordingly assigned to my use. The object-glass was that of the refraction circle of the United States Naval Observatory. Having beeu taken from its tube and conveyed to the station at Des Moines it was there fitted to a temporary wooden tube mounted in such a manner as to command the sun during the eclipse. This glass has a clear aperture of 5.9 inches in diameter, and a focal length of about eight feet seven inches, according to a rough measurement which I made since my return to this city. The eye-piece I employed, one of a set furnished also by the observatory, was a positive, or Eamsden, eye-piece, in the field of view of which 0.2G inch is found to sub- tend to the eye .an angle of about 13 36', which corresponds to a virtual or compound focal length of 1.1 inches. The magnifying power of the instrument was, therefore, not far from 94. The tem- porary wooden tube was square in cross-section, and the eye-piece was mounted on a square piece of board fitted to the interior of the tube. The focal adjustment could be made by sliding this piece of board a little to and fro in the tube, and a thin narrow wooden wedge introduced near the upper right-hand corner of the piece of board served effectually to secure it in its place. The square wooden tube was mounted so as to swing at its middle in a wooden gimbal constructed of four pieces of stout plank, and this gimbal turned on a nearly horizontal axis pointing not far from 166 KEPORT OF MR. J. HOMER LANE. north and south, being supported by a pair of heavy upright timbers or posts, set firmly in the ground. The tube was well counterpoised or balanced, and was steadied by means of a pair of braces extending from the tube to the posts. Each brace consisted of a long lath of soft pine wood. The connection of the lath to the post was made by a common wood screw, passed through a hole in the lath and set into the post. Another wood screw, having had its head rasped or filed down till the head of the shank was reduced to a blunt point, was driven into the square tube, by the pointed shank, not far from the eye end. The screw so set in the tube was embraced by a long longitudinal slot made in the lath. The slot, while wide enough to admit the screw bodily, was narrow enough to pinch it by a rather gentle pressure due to the elasticity of the lath alone. This arrangement was effective in preventing oscillations, aud allowed the telescope to be moved by hand with not much effort and not much, false motion. Screw nuts of wood were provided, by which the braces could be clamped at the slots, but these were not used any further than they may have served to guard against the lath working off from the screw. These dispositions were all made by Professor Newcomb, and were, in the main, executed before my arrival. On my way to Des Moines it occurred to me that, in looking after the space immediately con- tiguous to the sun's luminous surface or photosphere, something might possibly be gained by occupying part of the field of view of the telescope with a piece of colored glass or smoked mica, bounded by a straight edge. The crescent of the uncovered part of the sun could then be viewed through the colored glass, and on bringing the cusp near to the edge of the glass we would avail ourselves of the artifice by which Dawes made his discoveries in the solar spots, and Clark brought to light the companion of Sirius. A hasty review of the question satisfied me that before totality at Des Moines the cusps would be carried eastward across a line nearly parallel to the line joining them, in consequence of the moon's apparent motion, less rapidly than the sun would be carried westward across the same line by his diurnal motion. This is really the case, but, in the hurried judgment which alone there was any time to form, I somewhat overrated the difference. I will here give the comparison which I have made since the eclipse, at the same time making plain in what manner the screen glass was applied. In Fig 1, let C represent the center of the sun's disk, and about the same center let F B'N E be a circle described with a radius of 47".3, the quantity by which the apparent semi- diameter of the moon seen from Des Moines at totality exceeds that of the sun, aud let A B D E be the apparent track of the moon's center on the sun's disk, and N the north point. My own calculations from the American Nautical i Almanac, according to which the court-house square observa- tory in Des Moiues, at the nearest approach of centers, was about seven miles (.00176) from the axis of the shadow, meas- ured at right angles, give N C B=63 40', and N C E=100 44', and the figure is drawn to the true proportions. Now, suppose a circular arc, F A, whose radius is equal to the radius of the moon's disk, to be drawn through the moon's center at A, tangent to the circle F B N E at F. Then it is evi- deut that if the radius F C be prolonged through G it will meet the sun's limb at the cusp. The motion of F is, therefore, a reduced representation of that of the cusp reversed. Drop the perpen- dicular F L upon C B. B L differs very little, especially for the northern cusp, from A B, so long- as the crescent is less than 70 or 75, and the greatest velocity with which F approaches the tan- gent line H B K is very nearly the velocity of the moon's center along A B. Hence the greatest velocity with which the cusp crosses a line parallel to H B K is such a velocity as would traverse the diameter of the sun's disk in about the period of 178 8 , which it would take the moon's center to traverse the diameter of the circle F B N E. But the time occupied by the sun's disk in crossing the same line by its diurnal motion from contact to contact was only about 147 s . The two velocities are nearly in the ratio of six to five, and the cusp was, at the near approach of totality, still carried westward across a fixed line parallel to H B K with a velocity about one sixth that of the diurnal motion across the same line. The angle made by H B K at the time of totality, if my calculation is correct, with the sun's vertical diameter, was 24 51' from the vertex toward the right. The OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 167 Fi K . ' angle at which the straight edge of the colored glass was set, according to a measurement made after the eclipse, was 23. This nearness of coincidence was in part accidental. Moreover, the inclination of the glass was measured with the telescope horizontal, and wheu pointed to the sun (due west at the time of totality) the vertical diameter of the field of view was changed by nearly half whatever angle of azimuth existed between the meridian and the horizontal axis of the gimbal on which the telescope moved. This angle, however, was at least small, if it existed at all. My plan of observation before totality was to set the telescope with the cusp, seen through the colored glass, approximated as closely as might be to the edge of the glass, and then allow the cusp to approach still more closely to the edge by the excess of the diurnal motion across it over the opposed cusp motion. But this programme was not as closely realized as it might have been had I had more time for preparation, and for careful preliminary study of the conditions. The prepara- tion ought to have been so complete that the cusp could be continuously and accurately followed by the edge of the glass. With the telescope originally intended for my use there was hardly time to have made any preparation at all for this way of observing, there not being at hand a suitable instrument-maker. But the temporary arrangement which Professor Xewcomb placed in my hands, as already described, afforded great facility for carrying it hastily into effect with the aid merely of a carpen- ter. The colored glass, which I had not provided myself with for the reason that the method did not occur to me till after I was on my way, was fortunately at the disposal of Dr. Hilgard, of St. Louis, who also accompanied the expedition, and had an extra glass which he kindly loaned to me for the occasion. It was a piece of deep-blue plate-glass, about one-eighth of an inch thick, as near as I can judge, and showed the sun's disk very soft and easy to the eye. This glass is shown of half size at a b c d, Fig. 2. It was fastened in the manner there shown into a wooden slider e f half an inch thick, also shown of half size, as is likewise the slot g h I A- / m, with some enlargement of the latter on the side remote from the eye. The dotted circle q r shows the field of view of half its actual size, and by moving the slider along the line e f, the blue-f glass abed could be made to cover the entire field of view, or any desired part of the field, or could be thrown entirely out of the field on either side. The slider e f was applied to the surface of the before-mentioned square piece of board that was to carry the eye-piece, on the side, of course, next the eye, and was held in place by a wooden cleat laid across it in the manner shown in quarter size, Fig. 3. This cleat was three-fourths of an inch thick, and was screwed to the square piece of board after having been recessed half an inch deep so as to Fig. 3. embrace the slider without undue pressure, and the Kamsden eye- piece was then screwed into a hole cut through the cleat. Bearing in mind the inversion of the sun's image, the left-hand edge a 6, Fig. 2, of the blue glass, would come into use before totality. This edge was, therefore, ground straight and nearly smooth on the oil- stone. The blue glass was adjusted to the focus of the eye-piece, and the sun was afterwards brought into focus by moving the square piece of board a little to and fro in the tube. The blue glass was much thicker than it would have been desirable to employ for this purpose, since the plate displaces the focus of the cone of rays traversing it, by a space equal to one-third its thickness for glass, whose index of refraction is 1. Hence, in adjusting the solar focus some time before totality, the blue plate was slid entirely from the field of view, and the screen glass belonging to the eye- piece, a red glass, I believe, was used to protect the eye in the common manner by placing it between the eye and eye-lens. This was done with a view to leave the open part of the field of view after- wards in good focus, in preference to the part which would be covered by the blue glass for showing the sun's crescent. Yet, after removing the red glass and sliding in the blue glass, the definition of the details of the solar spots appeared equally as sharp and good as before, and my inference was that the eye readily accommodated itself to the difference of focus produced. Taking the change in the i li e k I/ (* '. r > S a. d m 168 REPORT OF MR. J. HOMER LANE. place of the focus at one twenty-fifth of au inch, I have found, by direct experiment with the same eye-piece since, that my eye does readily accommodate itself to that difference of focus. As the virtual focal distance of the eye-piece is about 1.1 inch, it is only the difference between the stellar focus of the reversed eye-piece, and the focus of the same for an object at twenty-nine inches, a range easily commanded by the eyes of most persons. These things being arranged, as the time of totality drew near, the blue glass entirely covering the field of view, I began by trying the skylight, with the crescent in the field, by a cautious side glance of the eye while moving the blue glass, by its slider e /, so as to open the edge of the field. The light was yet too bright for the eye to endure. Soon I used a very light red glass as a protec- tion to the eye in these trials. As soon as admissible more than half the field was uncovered. My attention was confined, up to the beginning of totality, to the region of the northern cusp, which, of course, as inverted, was at the lower side, the crescent on the right. At last the moon's limb was seen putting boldly out into the open field beyond the blue screen, in correspondence, of course, with the inner limb of the crescent. The time of this was 10 1 ' 57 m 19 s by chronometer Negus No. 1281, which, compared" with the time of second contact as noted by Professor Hilgard, gives l ra 13' before totality. Unluckily, I failed to recollect positively whether the light-red screen glass was then used. My impression is it was not, and it certainly was not afterwards. The moon's limb, as then seen, was not a barely percepible outline, but was abundantly palpable to the eye, and might evidently have been seen earlier. Having no assistant, I think I must have taken twelve or fifteen seconds of time in going four or five steps to the chronometer and noting the time with due care before I could resume my place at the telescope. There was, therefore, scarcely over a minute left before the beginning of totality, perhaps not quite that, and it may be as well that, in the anxiety of the moment, 1 did not know the time was so short. It was a somewhat hurried work to bring the cusp to close proximity to the edge of the blue screen with a view to secure a review of as much as possible of the moon's limb while least elevated above that of the sun. A tolerably good approximation was obtained, but some few degrees of the moon's limb intervened between the cusp and the edge of the screen. This remark will at least apply to the important period of the last say ten or twelve seconds before first internal contact, perhaps more. The excess of the sun's diurnal motion across the edge of the screen over the cusp motion across the same was so much smaller than my first rough estimate had led me to anticipate, that it came little, if any, into play for bringing the cusp up to the edge, but this same circumstance gave a useful permanency to such an approximation as I did obtain. Of course, to perfect the arrangement, the screen should have been provided with a slow motion for readier command of the adjustment. After the moon's limb had appeared and I had returned from noting the time, and had got the telescope tolerably readjusted, I looked carefully for the appearances next the moon's limb. The light of the corona remained almost quenched by the still superior light of the sky. It had been thought possible that this condition might afford an opportunity to see the regular circular, or level outline, of a low solar atmosphere, if such existed to be seen. But no impression of such an appear- ance was made upon my eye. . None of the light above, or exterior to, the moon's limb, that I no ticed, prevailed largely over the light of the sky, until within some five to eight seconds, as near as I can judge, before internal contact of the limbs ; and when it did begin to prevail it blazed up quite rapidly and to a considerable height at once, say from 10" to 20", yet not, as it struck me, with a regular outline. The general impression upon me of this first outburst for it was only a general impression was more as if it was built up of tongues of flame. The brightness, though by no means dazzling, was such as to make it not impossible that some kind of colored screen glass might have favored the observation of appearances which I did not see. The color appeared mainly white. The estimate of 10" or 20" for the height could not be made at the time, as I was not accustomed to the power employed. I have tried to form a rough judgment in regard to it since, by using the same eye-piece with the objective of a small spy-glass, to view a circle drawn on paper, and placed at the distance where it gave to the eye-piece an image of the same size that the moon's outline gave in the telescope, and then cutting a slit in the paper through which to view a gas-light. In these observations no part of the crescent of true sunlight got beyond the blue screen into the open field. In the last second or two before totality, the length of arc of the moon's limb included between the cusp and the edge of the screen increased very rapidly ; and to this may OBSERVATIONS OP THE ECLIPSE OP AUGUST 7, 1869. 169 have been due the impression produced upon me that the cusp ran away from the edge of the screen, which I concluded was impossible, if the edge of the screen was really set parallel to the tangent at contact of limbs. At the instant of contact some 20, perhaps, of the moon's limb (10 on each side the point of contact) remained behind the screen, which was then instantly slid entirely from the field of view. [Nothing was now seen at this part of the limb to modify what had been seen before- Satisfied of this I swept the circuit of the wonderful spectacles presented in the corona, but returned immediately to the very peculiarly formed and comparatively small red clouds first seen in the im- mediate region of the point of first internal contact. Leaving to others the sketching of the general features of the phenomenon, I selected a very small number of points on which to concentrate my attention with a view to watch for any visible changes. In this I was partly prompted by a query which had rested on my mind for two or three months previous whether the coronal light might not be of the nature of our auroras, only on an immensely grander scale. One or two of these smaller red clouds were scrutinized very closely for some time, but not the slightest point of change was detected. The several clouds at this part of the limb had a peculiarity of conformation of their own which seemed to distinguish them from all the others which met my eye in sweeping the coro- na. The somewhat slender elongated body curved or bent, will no doubt be seen in the photographs, in one of which in fact, seen on the following day, I recognized these bodies. The boundary of the cloud seemed to be quite sharp and well defined, or at least with no notable shading off. This I state from recollection, and not from any note purposely taken of it at the time. Becoming convinced that the red clouds I was scrutinizing were to be an apparent fixture for the period of totality, I turned my attention to the agglomerations of white light in the corona, and fixed upon two of these which were remarkable for their small size and the comparatively dense accumulation of light in them. These were situated about 80 from the vertex toward the right, as seen inverted in the telescope. In appearance they might well be compared to small telescopic comets with tails of some length, but without a head, and with no distinct indication of a head at one end rather than the other. They were not far from radial in direction relatively to the sun's center whether exactly so I did not remark at the time but appeared completely isolated, and had their origin far above the limb of the moon ; so far, at least, that though that part of the limb must have been approaching them, if their height above the sun's limb remained constant, the ap- proach did not attract my attention. I referred them two or three times to the profile of neighbor- ing lunar mountains, so far as to make it evident there was no such relative motion as must have been expected had they been anything floating in our atmosphere. They manifestly belonged to the heavens, and I made no doubt were to be classed with the other parts or aggregations of white light in the corona. These two bodies I scrutinized closely for some time, and, as I suppose, to the end of totality. The form, dimensions, and appearance of each, and their distance apart, were in constant review ; but not the least change in either respect was seen. It would be in vain for me to try to estimate the length of time occupied either with these objects or with the red clouds particularly watched. As to the distance apart of these two white comet-like objects, I judged, after the largest solar spot had been uncovered, that they would have included between their centers the nucleus of that spot, but not the penumbra. I had no means of taking any measures, nor would it have been easy to take measures without sacrificing the watch for the presence or absence of changes. In order, however, to reproduce as near as practicable what I saw, I have laid down upon paper a circle of the same size that the moon's outline had in the focus of the object-glass almost an inch and holding this up to the light in the field of view of the same eye-piece used in the telescope, have tried to lay down with a pencil the dimensions and situations of the two objects. The following is the result I got in this way: Length of each cometoid light, 130". Height of its origin above moon's limb, 100" to 80". Distance from center to center of the two, 50" to 40". Perhaps the height above the moon's limb should be taken at about half a minute before the end of totality. The estimate of 50" to 40" here made for the distance apart of the two objects may be considered entirely independent of the one first given referring to the solar spot. In that case the 22* 170 REPORT OF MR. J. HOMER LANE. judgment comparing with tbe spot AN as checked by selecting a pair of scratches on the blue screen glass in the field of view, before the eclipse was over, whose interval was judged not far from equal to that of the two objects, and then bringing the solar spot between them. The end of totality having arrived, I thought it well to ascertain how long the eastern, or far limb, of the moon could be seen. With this view I continued to watch that part of tbe limb coin prising most of the lower right-hand quadrant, and some adjoining part, perhaps, of the upper right-hand quadrant, as seen inverted in the telescope. For some little time it continued to be strongly marked ; for a considerable length of time it was easily seen ; and for a still longer time it could be unmistakably followed by the aid of a little motion given to the telescope. As the last faint traces were being obliterated I noted the time by Negus No. 1281, 11" 3 m 30. Comparing this with the time of third contact as noted by Professor Hilgard, I And it to have been 2 5" after the end of totality. This time is so considerable that unless the observation has been confirmed by others, I would not wonder if it should be thought liable to the uncertainty that I might have made a mistake in noting the minute. I can only say that I tried to take good care in noting the minute, and that I have no reason to doubt the time is as 1 have given it. Respectfully submitted. J. HOSIER LANE. Commodore B. F. SANDS, U. S. N., Superintendent U. S. Naval Observatory, Waxhington, D. C. OF MR. . S. GILMAI, JR. REPORT OF MR. W. S. GIL MAN, JR. Sioux CITY, IOWA, August 10, 1869. DEAR SIR : I Laud you herewith a report of the total eclipse of the sun on the 7th instant, as observed by myself and eight others at St. Paul Junction, Plymouth County, Iowa, twenty-five miles northeast of this place. I took up niy position on the 4th instant, on the northeast quarter of section 16, township 92 north, range 45 west, and estimated my longitude to be 19 5' 45" west of Washington, assuming 16 34' 1".4 to be the longitude of Des Moines. My latitude I estimated at 42 47' 30" north. In arriving at these values I used the new map of Iowa, issued the present summer by Colton, of New York. My telescope was set upon the west side of the house of Mr. N. E. Farrell, at a point twelve feet south of the north line of section 16, and seventy-five feet east of the west line of the same section. DESCRIPTION OF INSTRUMENTS. There were in the party three small telescopes, of apertures varying from 1 to 1.2 inches and magnifying from eight to ten times. I had brought with me my 4-inch telescope, made by Alvan Clark, of Cambridgeport. Beside these instruments we had a good binocular field-glass. All the instruments were substantially mounted on tripods or steady rests, in such a manner as to allow of easy movement in any desired direction, and their eye-pieces were slightly smoked. Neutral tinted shades and deeply smoked glass were also used during the earlier and later portions of the eclipse. By means of a good thermometer, of B. Pike's make, I took record of temperatures for several days preceding and following the eclipse, as will be found on reference to Schedule A. The ther- mometer was exposed to the weather on the north side of Mr. FarrelFs house, and screened only from direct light of sun. Its height above the ground was five feet six inches. When noting contacts I used S. Hammond's mean time gold chronometer, No. 300, which lost 1 8 .86 per diem. The instruments were distributed as follows: I observed with my admirably defining 4-inch achromatic of five feet two inches focal length, charged with a power of fifty, and carrying a ruled micrometer of glass, giving angles of position for every 45, and measuring arcs of 15" when used in connection with my instrument. My mount- ing was Mr. Clark's usual portable equatorial, without circles or clock work. The power I employed gave a field of view of about 43' of arc. My principal aim was to get observations of (1) the times of contact; (2) the size and positions of red flames; (3) the outline and general extent of the corona, and (4) the colors of both the flames and the corona. Daniel T. Oilman confined himself to noting time by the chronometer, for which he had been qualified by previous practice with me. N. E. Farrell, a member of the Powell Colorado exploring expedition of 1868, kept the record of the thermometer. He used a field-glass at various times, to which instrument he was well accustomed, having employed it constantly during the expedition referred to. Leon Vincent, of the civil engineer corps of the Iowa Falls and Sioux City railroad, employed a telescope, with which he was well acquainted, having an aperture of 1.1 inches, and a focal length of 10 inches. It gave a direct image, and magnified about ten times. Lucius C. Phelps, associated with the above in the engineer corps, used a telescope of J-iiich aperture, having a focal length of 10 inches, and magnifying about ten times. This instrument gave an inverted image. Vincent Wood used a telescope of 1.2 inches aperture and 20 inches focal length, which gave a direct image. The power of this telescope was a little, though not much, above the two just mentioned. 174 REPORT OF MR. W. S. OILMAN, JR. Eugene Lockliii and Seymour Ball observed without instruments for flames, extent of corona, stars, and planets. Mrs. N. E. Farrell observed especially for the approach of the dark shadow in the air, for stars and planets, and assisted in keeping the thermometrical record. Specific duties were assigned to each of the above by written schedules, which were carefully studied a day or two previously. WEATHEB DURING THE ECLIPSE. At 2 p. in. the sky cleared overhead, and at 3 p. m. there were no clouds. A slight haze remained, which assisted the definition of our instruments. On the southeast horizon the hnze was thick and resembled a fog-bank. THE ECLIPSE FIRST CONTACT. At 4 h 57 m 9 s by my chronometer, (see Schedule B,) I observed with my telescope a small black speck on the preceding limb of the sun's disk, at the precise point to which I had been for some minutes directing my attention. At first I took it to be the result of a slight tremor of the sun's limb produced by an atmospheric cause, though at the time the atmosphere was steady and the definition all that could be desired. s. w. E. W. N. I. FIRST CONTACT, 4*1. 57m. 95. N. Y. M. T. At 4 h 57 m 12 s .o, or 3.5 seconds later than the above time, the impinging limb of the moon rendered the nature of the black point apparent. The appearance of this small point is given in the above sketch, No. 1, in which is also shown the moon's limb, visible away from the sun's disk a few minutes from the point of contact on either side. Though I had looked with great care for the approaching moon some minutes previous to contact, I N. 2. APPEARANCE OF THE SUN'S DISC AT 5(1. 5m. N. Y. M. T., SHOWING FOUR PROJECTIONS ON THE MOON'S LIMB. saw nothing of it until after 1 had seized the black excrescence represented in the sketch, (No. 1.) Mr. Farrell noted the time of first contact independently, by means of his field-glass, at 4 1 ' 57 m 18 s chronometer time, or 9 seconds later than myself. As the moon advanced on the sun's disk, it was apparent that its limb was very rough. I made a sketch of its appearance at 5 h 5 m chronometer time, which I append herewith, (No. 2.) There were distinctly visible at this time near the center of the dark limb of the moon four projections of unequal altitude and varying extent. The second prominence from the north Avas the highest, and measured about three seconds of arc, as nearly as I could estimate. It was this OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 175 poiut which first touched the sun's disk, as shown in sketch No. 1. I suppose these elevations to have been the Montos d'Alembert of Beer & Mueller's large map of the moon. I roughly estimated that the distance from I) to A was about 1', from C to B 1'.25, while the two sets of prominences appeared to be separated by an interval of 1'.75. The ridge at B was of greater extent and more jagged than the others, though not so high in relief above the moon's surface as that marked A. These ridges were witnessed by several persons at various times, all agreeing both as regards their number and relative distances. They were seen during the entire transit of the moon's following limb. SPOTS ON THE SUN. There were, during the eclipse, four groups of spots upon located on a diagram during the hour pre- ceding the first contact, with the intention of recording their exact times of disappear- ance and reappearance. Sketch No. 3 is a copy of this diagram. 1 have numbered the groups from 1 to 4, and reckoned the times of disappearance and reappearance from those portions of the groups indicated by a cross, (x). In group No. 1 I reckoned the disap- pearance from the minute bright point in the penumbra of the large spot on the following side of the phenomenon. This point of bright matter was an interesting object. The details of the spot are given in the corner of Sketch No. 3. In estimating the disappearance and reappearance of group No. 3, 1 reckoned from the larger of the two following spots on this triple group. In group No. 2 1 took the largest spot on the following side of the group. In group No. 4 a remarkable object, by the way, of which more anon I selected the southern edge of the umbra of the great spot. The times will be found in Schedule B. the sun's disk, all of which I s had DIAGRAM SHOWING SPOTS ON THE SUN DURING THE ECLIPSE, .AS SKETCHED ONE HOUR PREVIOUS TO THE FIRST CONTACT. APPEARANCE OF THE SOLAR SURFACE. Many times during the progress of the eclipse was my attention arrested by the striking appear- ance of the surface of the sun. The pores of the photosphere were visible, with unusual distinctness, to within a few seconds of the edges of the penumbrae surrounding the larger spots. This phenom- enon was more striking as the eclipse progressed. The facula? clustering around the large spot numbered 4 in the diagram were very prominent, and suggested the comparison to lumps of plastic white clay, or plaster of Paris, scattered around its borders, or to the little lunar peaks in the vicinity of Plato and < 'assini, as they appear when just within the illuminated portion of the moon's disk, at the first quarter. The encircling ridges of facuhe seemed to stand out in bold relief from the sun's general surface. APPROACH OF THE TOTAL PHASE. At o h 40 1 " chronometer time, which was twenty minutes previous to totality, cocks were heard to crow, and chickens prepared for the night. A herd of cattle also came in from the prairies, where they had been feeding all day, and went into the barn-yard near by. At 5 11 48 m chronometer time, the gloom deepened rapidly, and the sudden coolness of the atmosphere struck me with surprise. The feeling was as if one was about to enter a cavern. 176 REPORT OF MR. W. S. OILMAN, JR. A few minutes previous to totality the horizon changed color, as it is frequently seen to do on the approach of a storm. To the south the sky became of a rose-violet hue at 30 from the horizon. At the same elevation in the northwest a grayish-violet tint prevailed. Perfect silence reigned during the remaining moments of sunlight, and continued even for some instants after the subsequent captivating scene of beauty burst upon our sight. During this still- ness Mrs. Farrell distinctly saw the moon's shadow rapidly approach- ing in the air. It appeared to go upwards from the western horizon like the lifting of a dark curtain. As the thin solar crescent was about to vanish I watched care- fully for the phenomenon of Baily's Beads. The atmosphere was very steady, and the limbs of both sun and moon were admirably defined. The roughness of the moon's limb produced an approach to the phenomenon as the several projections closed in upon the remnant of the solar disk, but no appearance of beads was noticed. With a less favoring atmosphere I doubt not the sight would have been witnessed. Mr. Farrell, however, using a field-glass, noticed the beads, and compared them to drops of water running together and quickly disappearing. He made the annexed sketch of the PARALLEL TO phenomenon in my note-book soon after the ending of the eclipse. 4 MINUTE CRESCENT NEAR THE SUN. About half a minute preceding totality, possibly somewhat less, Mr. Vincent left his position and came to me exclaiming that he saw a miniature crescent-shaped star under the moon, and that 1 must come and verify his observation. So interested was I in my own work that I paid little attention to Mr. Vincent's announcement, but on his returning a second time, more urgent than ever to have me look at the object, I did so in a hurried manner, using his glass. I detected nothing in the few seconds I gave to the search. According to Mr. Vincent's drawing, made soon after the eclipse, the little moon was located one and a half times the moon's diameter from its limb, and to the left of a line drawn perpendicu larly down to the horizon. I do not think I searched the sky as far away from the moon as the distance given. During totality the object was forgotten, but shortly after the third contact lie readily picked it up in the same locality. TOTALITY. The second contact, which was well observed, took plack at 6 1 ' O m 45 S .5 chronometer time. Owing to an unfortunate error in my not removing the dark shade instantly on the extinction of the sun, I saw nothing of the formation of the corona. The gradual appearance of this beautiful feature of the eclipse was observed by Messrs. Farrell and Vincent. An anvil-shaped rose-colored flame or protuberance and a large portion of the corona 'if ere seen several seconds previous to the xcronil contact. As soon as I had removed my dark shade the view presented to my eye in the telescope was one of indescribable beauty. My attention was chiefly attracted to the large anvil-shaped protuber- ance, which I at once recognized as occupying that portion of the sun's limb in the region of which I had previously seen the brightest double facuia, indicated in Sketch 3 by the letter B. It appeared like a monstrous glowing coal, dotted here and there, particularly on the southern side, with minute flakes of brilliant deep crimson. It was my expectation that the rich masses of facuia! visible in the sun's southern hemisphere, near the eastern limb, on the 26th of July last, and indicated by the let- ter A in Sketches 5 and G, would be near the western limb on the day of the solar eclipse. The appearance of striking rose-colored flames in this vicinity would, it seemed to me, render plausible the theory of a connection between these objects and portions of the sun's surface that have the OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1809. 177 appearance of being unusually agitated. It was, therefore, with considerable interest that I noticed on tlie 5th, Cth, and 7th of August, in the southwestern quadrant of the sun, intensely bright, white ridges approaching the limb, as represented in Sketches 7, 8, and 3. s. JULY j6<J 6>>. W. M.T. TWO SPOTS AT A SURROUNDED BY FACULAE. NO FACULAE DETECTED ELSEWHERE. OBSERVATION MADE THROUGH CLOUDS BEAUTIFUL LINE OF SMALL BLACK POINTS AT B. W. THREE SPOTS WELL SEEN THROUGH CLOUDS. FACULAE SURROUNDING A AND FOLLOWING. FACULAE DISTINCT AT B. AUG. . W. M.T. AUG. 6d 4 h. W. M.T FACULAE FROM 235- TO 270'. AND VERY MARKED AT 245-. TWO BRIGHT MASSES AT LATTER POINT. SPOTS AT B. C. & D. AT C, SPOT OF CONSIDERABLE SIZE AND INTEREST. NO FA- CULAE SEEN IN NORTHERN HEMISPHERE. 7 TWO BRILLIANT FACULAE AT 250" (?) DIFFICULT OBSERVATION OWING TO CLOUDS. N. So deep was my interest in the subject that I had made the condition of the solar disk a study from the middle of June to the first week of August, and especially on the 24th, 25th, and 2Gth of July and the 5th of August, with a view of forecasting the, positions of protuberances during the 23* 178 REPORT OF MR. W. S. OILMAN, JR. eclipse, which forecast I made on the after- noon of the 5th, as given in Sketch 9, herewith- The impression upon my mind has, for a long- time, been that the rose protuberances are in the nature of exhalations from portions of the surface in a high state of agitation, such as witnessed in the vicinity of faculous ridges and spots. Having made the forecast referred to, I indicated with. a cross (x) two prominences w which, I expected, might be unusually large. The eastern one of these would, as I thought, be produced through the medium ot the agi- tated ridges at D, pictured in Sketches 10 and 11, which, on the afternoon of the 7th of Au- gust, would, if sufficiently persistent, occupy, by virtue of the sun's revolution, a position on the eastern limb, say near 25 north latitude. The western flame, which I marked in the same manner, was located in south latitude 10, for the reason that the large spot at B, Sketch 7, would, from the same cause, during the eclipse, occupy this portion of the sun's limb, and from it tions that would be readilv visible. N. ROSE PROTUBERANCES AS FORECASTED AUGUST 5, .869. I surmised there would be exhala- W JULY ?4<i W. M. T. TWO SPOTS AT A FOLLOWED BY BRIGHT FACULAE. FACULAE VERY BRIGHT AT C, D & E, ESPECIALLY AT D. AT p. 2' FROM LIMB, TWO BRIGHT MASSES OF FACULAE. VERY MUCH CONDENSED. IO JULY 2 5 <<. ih. W. M. T. NlP A BRIGHT RIDGE OF FACULAE HAS JUST APPEARED UNDER THE EQUATOR ON EASTERN LIMB AT G. BRIGHT RIDGE ALSO AT H. FOLLOWING A, FACULAE MORE BRIL LIANT. ATMOSPHERE HAZY N. The first of these marked flames I failed to verify, though it may have been seen by others. 1 have, the more hope that this will prove the case since out of six protuberances seen by me I noted the positions of but four from want of time. In regard to the second marked flame, this also was not seen, and doubtless had no existence, as the locality was carefully studied by me, and but one flame (A) appeared in this, the southwest- ern quadrant of the sun. The protuberance, however, located over the bright double facula further south, was the great anvil-shaped flame already noticed. . The fact of the utter absence of rosy mat- ter in the vicinity of the spot may indicate an imcard current in the case of spot openings in oppo- OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 179 sitiou to aii out tea rd or upward OIK- iu the case of factilous agitations. The pointing of the anvil toward the equator may in this connection possess some significance, indicating, possibly, a mon- ster current toward the large spot 13, under the Equator. I have reason for believing that the protuberances forecasted at B, (', and D had their true counterparts in those observed during the. eclipse, as represented in Sketches 1^2. 13, and 14. I s. i? B ROSY PROMINENCES AI 6h. im.45s N. Y. M. T TREMULOUS LIGHT AT A. ROSY PROMINENCES AT 6h. am. 15,. N. Y. M. T. NORTHERN END OF A COM- POSED OF FIBROUS LINES OF FLAME. West. ROSY PROMINENCES AT h. am. 455. N. Y. M. T. NEW FLAME AT D. East. N. should here remark, that having made my forecast, I laid it away in my portfolio, where it was not disturbed until the morning of the 9th, when I first became aware of the coincidences referred to. The protuberances were uniformly of an orange color, and, as It seemed to me, of the precise tint of the glowing coals in an anthracite grate. There was, however, in the case of the three north- ern protuberances, at least, the remarkable addition of small crimson scales or flakes of astonishing richness of color. These scales seemed to have no connection with the protuberances, though they were projected upon them. They were not seen, however, disconnected from the flames, and their separate character may have been more apparent than real. I was deeply interested in them, and have no doubt that the phenomenon of crimson flakes was truly witnessed, and that my eyes were not deceived. 180 REPORT OF MR. W S. GILMAN, JR. At the bases of the flames sulphurous lines were discernible, as also at the tapering, " wispy' 7 eud of the anvil-shaped mass pointing to the equator. I saw no changes in any of the llames, except an apparent wavy motion in the pointed end of the large one. Though I have called them inter- changeably flame* and protuberances, they did not appear like names, but possessed a clear, unchang- ing, almost harsh outline, as if cut out of some solid substance. 1 noticed a llaky structure in the large protuberance, and was strongly impressed with its resemblance to glowing embers, dotted over with minute crimson spots, as stated. I was not prepared for such stability on the part of the protuberances as was witnessed. I made the positions of the four protuberances by estimation as follows, vi/. : A, anvil-shaped mass, 230 235 B, 140 Q, 120 D, 320 THE COKONA. The general outline of the corona was a trapezium, with the widest side to the southeast. (See Plate XII.) There were also lesser projections on the four sides, as well as several small indentations. The longest masses of light coincided very nearly with the north and east points, at the middle of totality. Mr. Farrell also noted the same peculiarity. The corona was composed of an infinitude of fine violet, mauve-colored, white, and yellowish white rays, issuing from behind the moon. I detected no clouds in it. The exterior edge was very jagged in appearance, but did not possess a harsh outline, having, on the contrary, a soft blurred look. This was quite contrary to my expectations, as, from all the drawings of eclipses 1 had ever seen, I was led to expect a well-defined and truly circular halo of light, extending to an equal dis tance on all sides. Mr. Farrell described the appearance of the corona verbally, as follows: "It was a silvery-gray crown of light, and looked as if it was the product of countless fine jets of steam, issuing from be- hind a dark globe. Near the moon's disk, the light seemed almost phosphorescent." During totality the seconds on our watch faces could not be read without the assistance of the lamps placed in the windows of the house to aid us at this juncture. The time could with difficulty be told by the larger hands. MINUTE OBJECT SEEN NEAR THE SUN. A few moments after the formation of the corona, a minute object was noted independently by four of the party, and should be here mentioned. A small but exceedingly bright point, like a star, was witnessed by Messrs. Farrell, Phelps. and Locklin, and Mrs. Farrell, during the period of totality. It appeared near the limits of the corona, below the moon's disk direct vision and in the region of the anvil-shaped protuberance. Mr. Farrel judged it to be about one-sixth some say one-tenth the size of Mercury ; which latter star was almost directly to the right of it, on a line parallel to the horizon. With the exception of Mrs. Farrell, all located the star a little to the right of the red promi- nence, or at about 230 from the north point, reckoning by the east. Each of the observers men tioned feels very positive that what he saw was truly a star. I cannot connect Mr. Vincent's miniature crescent with the small star of Messrs. Farrell, Phelps, and others, though, owing to Mr. Vincent's peculiar position, he may have located his object too far to the left. He was leaning on his left arm which may have led him to form in his mind a horizon inclining considerably to the true one. This would cause the location of a star below the sun to be too far to the left in his diagram. He estimated the object seen by him as three times as far re- moved from the moon's limb as the star noted by Messrs. Farrell, Phelps, ami others. The report of each observer was given to me shortly after the termination of the eclipse, and not iu the hearing of others. OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 181 PLANETS AND STARS VISIBLE. Of the planets and stars 1 saw but Venus. Regains, and Mercury. At no time during the eclipse did it occur to me to look for intra-niercurial planets. I saw Regulus with difficulty as a glimpse star, with the unaided eye. The reports show that seven stars were witnessed by our party, if we include the little brilliant below the snn. The gloom of totality did not impress me as being at all like that of moonlight, but rather like the somber light of an approaching thunder-storm, with this remarkable addition : an indescribably delicate mauve or violet-tinted glow in the portion of the heavens occupied by the eclipsed sun. Of the effect of color on the landscape I made no note. A sulphurous glow in the northeastern part of the sky drew my attention in that direction while I was arranging my screens, shortly after the second contact. It rose a few degrees above the horizon here, but not so high elsewhere. It pre- sented the appearance of a sunset after a heavy thunder-storm with the sun already below the hori- zon, and illuminating the under edge of the low hanging clouds. The phenomenon was generally observetl, and produced a great impression on all. THE THIRD CONTACT. By an unfortunate substitution of. a deep red for my ordinary neutral-tinted screen, 1 lost the third contact by about ten seconds, supposing I was witnessing the sun's hydrogen atmosphere, when I was observing his limb. Ascertaining my mistake I called time, and was given G h 3 m 45 K chronometer time ; my cousin remarking that he could now see to read the second-hand without the assistance of (lie lights in the window. I estimate 12* to have elapsed from time of third contact. The receding limb of the moon was less rough than the eastern one. Had it given any appear- ance like ' Baily's Beads" on revealing the first line of light from the sun's disk, I should certainly have detected it, so intently was I watching the point at which the sun's limb was to appear. A reference to the tliermometrical record kept by Mr. Farrell reveals the fact that the temper- ature of the air fell_from 7(i at first contact to C8 at eleven minutes after the reappearance of the snn. This latter temperature was the lowest reached during the eclipse. One hour later the ther- mometer marked 71, and at 7 p. in. it read C4.5. THE LAST CONTACT. The last contact occurred at 7 1 ' I" 1 36 s . W. S. OILMAN, JK. Commodore B. F. SANDS, IT. S. N., United States Naval Observatory, Wnxhinyton. 182 REPORT OF MR. W. S. OILMAN, JR. A. METEOROLOGICAL KECOKD. IN LOCAL TIME. AUGUST 5, 1869. Hour. Therm. Sky. Wind. Clouds. Remarks. 11 A.M. o 79.5 Overcast 8 NE. Dark Niuib. Shower. 12 M. 1 P.M. 2 P. M. 70.5 73. 75.7 Overcast HI Overcast 10 Overcast 9 E.NE. E. SE. Lighter Niuib. Lighter Niiul). Stratified. Wind blowing in gusts. 3 P.M. 78.5 Clear SE. Stratified. 4 P. M. 77. Clouds 3 E. Stratified. 5 P.M. 74. 5 Clouds 1 E. Stratified. 6 P.M. 71. Clouds 5 E. Stratified. 7 P.M. ee.7 Clouds 9 E. Stratified. 8 P.M. 68. Overcast 10 E. by S. AUGUST (i, 18(>9. 6 A. M. 64. Overcast 10 NE. Stratified. 7 A. M. 63. Overcast 10 NE. Stratified. Misty rain. 8 A. M. 64. . Overcast 10 N. NE. Stratified. Misty rain. A. M. 6-2. Overcast 10 NE. i Stratified. Misty rain. 10 A. M. 62. Overcast 10 NE. Stratified. Misty. 11 A. M. 64. Overcast 10 NE. Clouds higher. Misty. 12 M. 66. Overcast 10 NE. Still higher. Misty. 1 P. M. 68. Overcast 10 NE. Clouds higher. Misty. 2 P.M. 71.5 Overcast 9 NE. Clouds higher. Sun at intervals. 3 P.M. 72.25 Overcast 9 NE. Clouds thin. 4 P.M. 68.5 Overcast 10 NE. Clouds thicker. 5 P. M. 66. 5 Overcast 10 NE. Softer edgi'il. 6 P.M. 65.5 Overcast 10 NE. Softer edged. 7 P. M. 65. Overcast 10 NE. Softer edged. 8 P. M. 64. Overcoat 10 E. Softer edged. AUGUST 7, 1869. 6 A.M. 58.5 Overcast 10 E. 7 A. M. 60.5 Overcast 10 E. Thin overhead and in SE. moving N. 8 A.M. 64. Overcast 8 SE. Clouds thin moving rapidly to NW. S) A. M. 68.5 Overcast 10 SE. Clouds thicker. 10 A.M. 67. Overcast 10 E. by S. Clouds thicker. 11 A. M. 71. Overcast 10 SE. Clouds thinner. 12 M. 73. 75 Thinly " 9 SE. Sun visible at intervals. 1 P. M. 77. Thinly " 8 SE. Sun visible at intervals. 2 P. M. 75.5 Thinly " 5 SE. Snu visible at intervals. OBSERVATIONS OF THE ECLIPSE OP AUGUST 7, 1869. 183 Hour. Therm. Sky. Hour. Therm. Sky. c o 2 30 1'. M. 78. Clear 4 35 P. M. 68.5 C'lciir :! r. M. 7.">. r> Clear 4 40 P. JL 68.25 Clear 3 15 P. M. 70. Clear 4 45 P. M. 68. Clear 3 30 P. M. 7(5. Clear 4 50 P. M. 68. Clear 3 45 P. M. 76. Clear 4 55 P. M. 68.5 Clear 4 P. M. 74. 25 Clear 5 P.M. 69. Clear 4 05 P.M. 73. 5 Clear 5 15 P. M. 70. Clear 4 10 P. M. 73. Clear 5 30 P. M. 71. Clear 4 15 P. M. 72. Clear 5 45 P. M. 4 20 P. M. 71. 5 Clear 6 P. M. 4 25 P. M. 70. 75 Clear 6 15 P. M. 68. 5 4 30 P. M. 69. 75 Clear 6 30 P. M. 67. 4 31 P. M. 69. Clear 7 P. M. 64. 5 4 32 P. M. 69. -j & Clear 4 33 P. M. 68.5 | Clear 4 34 P. M. 68. 5 J Clear AUGUST 8, 1869. Hour. ITier. Sky. Wind. Clouds. Remarks. r 6 A. M. 59. Hazy to \. SE. 7 A. M. 04. Hazy SE. 8 A. JI. 68. 5 Hazy S. Clouds low on horizon. 9 A. M. 71.5 Ila/.y S.SE. Few faint milky clouds in N. 10 A. M. 75. 5 Cloudy 10 S. Few faint milky clouds in N. 11 A.M. 76.5 Cloudy 9 s. Few faint milky clouds iu N. 12 M. 80.7 Cloudy 8 s. Cum. all over sky. 1 P. M. 81.5 Cloudy 8 S.SE. Cum. all over sky. 2 P. JI. 81. 25 Clear 10 S.SE. Few Cum. in W. 3 P. JI. 81.2! Clear 10 S.SE. Few Cum. in SE. and SW. 4 P.M. 80. 5 Clear 10 S.SE. Few Cum. on horizon W. & NW. 5 P. M. 77. 5 Cloudy 6 SE. Very dark. 6 P.M. 75. Cloudy 8 SE. Dark iu W. 7 20 P. JI. 7:1. Clondy S. SE. Dark in W. 8 P.M. 73. Cloudy 8 S. SE. Clouds thinner iu W. i B. Comparisons for time. Times of contact and of disappearance and reappearance of sun spots. By the courtesy of Professors Newcomb and Harkness I was able to make accurate comparisons for time, both before and after the eclipse, at the temporary observatory on Third street, Des Moines. I had a similar opportunity at the Dearborn Observatory, Chicago, on the IGth, and finally at the Naval Observatory, Washington, on the occasion of presenting the foregoing report on the 20th of August last, when I was assisted by yourself and Professor Yarnall. Of these comparisons I give below those which I consider the most reliable. 184 REPORT OF MR. W. S. OILMAN', JR. Des Moines, July 31, 1860. Hammond No. 300. Negus No. 131! A. MI. . '< ' . 4 36 14.2p.m. 36 Negus fast of Des Moines mean time 6 18 13. 7 Des Homes mean time 3 17 46. 3 Longitude of temporary observatory 1 6 16. 09 Washington mean time -1 2-4 2. 39 Hammond fast of Washington mean time 12 11. 81 4 36 14. 20 Des Moines, August 12, 1869. Hammond No. 300. NY-jus No. 1319. //. Ml. 8. /'. W. x. 4 18 46. 1p.m. 9 19 Negus fast of Des Moines mean time 6 18 19.5 Des Moines mean time 3 40. 5 Longitude of temporary observatory 1 6 16. 09 Washington mean time 1 6 56. 59 Hammond fast of Washington mean time 11 49.51 4 18 46. 1 [3.] Dearborn Obserratory, Chiecif/o, August 16, 1869. Hammond No. 300. Observatory mi'iin lime dock. A. m. s. ti. MI. s. 4 39 35p.m. 3 45 30 Longitude west of Washington 42 14.26 Washington mean time 4 27 53. 26 Hammond fast of Washington mean time 11 41. 74 4 39 35 In this comparison the longitudes, from Greenwich, of Chicago and Washington, are taken respectively at 5 b 50" 1 26 S .65 and 5 1 ' 8 12 S .39. These values I obtained from Professor Safford and Professor Yarnall. United 8t<itex Xarul Obsei-ratory, WHxliiiiytnn, August 20, 1869. Hammond No. 300. Mi-:in ti ..... clock. A. m. s. I'- MI. s. . 3 23 34.5 3 12 Hammond fast of Washington mean time 11 34. 5 3 23 34.5 OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1369. 185 From the above I reach the following conclusions : Loss of chronometer Xo. 300, July 31 to August 12 = Loss of chronometer Xo. 300, August 12 to August 16 = (1.) 22.3 (2.) 7.77 (3.) 7.24 Loss of chronometer Xo. 300, August 16 to August 20 = From the first interval (1.) we obtain 22 9 .3 H- 12 days^= P.858 loss per diem. From the second interval (2.) we obtain 7*.77 4- 4 days = 1 9 .942 loss per diem. From the third interval (3.) 'we. obtain 7 S .24 4- 3 a .95 = l s .832 loss per diem. Taking 1 s . 86 as the daily rate at time of eclipse, and reckoning backward from August 12 to August 7, I find that my chronometer lost 9".5 between these dates, and therefore ll m 59 s is the amount to be deducted from all the times given in my report to reduce them to Washington mean time. Times of Conlaci. 1st contact 2d contact 3d contact 4th contact - Probable duration of totality at St. Paul Junction 2 47 s . Timed of disappearance and reappearance of sun spots. Chronometer. Washington moan time. k. in. s. ft. in. s. 4 57 9 ]>. in. 4 45 10 p. in. 6 45. 5 5 48 46.5 6 3 33 (!) 5 51 34 (?) 7 1 36 6 49 37 Disappearance. Group Xo 1. Group Xo. 2. Group Xo.3. Group Xo- 4. Reappearance. Group Xo. 1. Group Xo. 3. Group Xo. 2. Group Xo. 4. 24* Chronometer. 5 24 10 5 43 25.5 5 45 23. 5 5 58 35 6 17 58 6 40 12. 5 6 44 46 6 57 4.5 Washington mean time. 5 12 11 5 31 26. 5 5 33 24. 5 5 46 36 6 5 59 6 28 13. 5 6 32 47 6 45 5. 5 REPORT OF Mil. F. W. B A ED WELL, REPORT OF MR. F. W. BARDWELL. UNITED STATES NAVAL OBSERVATORY, Washington, D. C., September 20, 1869. SIR : I have the honor to submit the following statement, from notes made at the time, of the results of my observations of the total eclipse of the sim on the seventh of August last, in Bristol, Tennessee, near the central line of totality. Accompanied by Mr. Thomas Davidson, naval constructor United States ]$avy, I arrived in Bristol on tin- day of the eclipse, at an early hour in the morning, with an interval of time suffi- cient to select a suitable point for making observations. I found stationed near there a Coast Survey party with General Cutts, who kindly furnished me with the latitude and longitude of their station, which they had determined with every facility for accuracy. 1 also obtained from them a correction for clock error, fully answering every desired purpose. The point finally selected lor the purpose of observing the eclipse was on the brow of a hill moderately elevated above the surrounding country, with an extended view of the western horizon, at a distance from the stations of other parties, and far enough from the public highway to be free from the intrusion of idle visitors. The elevation above tide-water was about sixteen hundred and eighty feet, and thus favorable for a clear state of the atmosphere. I intended to give special attention during the time of total obscuration to the search for an intra-mercurial planet, and at other times to note any phenomena which would be useful for com- parison with the observations of others. For the purpose of detecting the appearance of any stranger planet, 1 had prepared a star- chart or map showing the relative positions of the line of the ecliptic, the apparent horizon, the Sun, Mercury, Venus, and the neighboring stars of not less than the fifth magnitude, within four degrees on either side of the ecliptic, and within ten degrees of the sun. I was also provided with a glass of magnifying power sufficient to show distinctly the spots on the sun's disk. In using this instrument it was merely strapped to a stake firmly driven into the ground, so as to secure steadiness of motion in directing it to different portions of the field to be examined. During the early part of the day the sky was partially overcast, and much anxiety was felt lest the grand event should be shorn of much of its interest; to observers by the obscuration of clouds; but about noon the sky became much brighter, and as the critical hour approached it seemed in the most favorable condition. Everything being in readiness, I was prepared to observe the first contact of the edge of the moon upon the sun's disk. It was arranged that I should observe the instant of contact and call time, while Mr. Davidson, observing the watch and counting seconds, should mark the time called. The record showed the time of first contact, corrected for clock error, to be 5 h 4 m 12 s , mean Washington time, which was sensibly later than was anticipated. The total obscuration of the sun commenced at 6 h l m 16 s , continued 2 m 30 s , and ended at 6 h 2 m 46 8 . During the progress of the eclipse numerous notes of the phenomena were recorded, some of which are here transcribed with the corresponding dates: "5 h 20 m . The edge of the moon seems slightly serrated or rough.. The disk of the sun is well defined, and shows eight spots in four groups. " 5 h 29 m . Visible diminution of light, "5 h 41 m . Light dimmed still more. The line between the shadows of clouds and the sunshine in the valley below is quite faint. "5 h 55 m . Light nearly the same as when the sun is hid behind a high hill just before setting." 190 REPORT OF MR. F. W. BARDWELL. During the time of totality the positions of Venus, the Moon, and Mercury appeared near enough in a direct line to guide me in the brief search for new planets, but none appeared in view. Mercury seemed to shine with the full light of a star of the first magnitude, and Venus very much brighter, while Regulus, which is classed as nearly of the first magnitude, appeared scarcely as bright as one of the second class, but it remained visible several seconds after the reappearance of the sun's rays. Almost immediately after the disappearance of the sun's disk a prominence, which I described at the time as " a rosette of bright purple," appeared at the edge of the moon Avhere the sun had disappeared ; then another on the lower limb of the moon that is, on the edge seen nearest the western horizon ; and lastly appeared still another at the point where the sun was about to reappear, while that first seen had nearly or quite disappeared. The order in which these appeared successively and disappeared showed that they belonged to the sun and not the moon a point perhaps well enough established already. The disappearance of the first of these before the reappearance of the suu, and the sensible interval of time before the third one made its appear- ance, showed that the apparent height of these prominences (first and third of those above described) was less than the difference between the apparent diameters of the suu and moon. With regard to the second of these prominences that is, the one seen below the lower limb of the moon if it was visible to observers near the northern limit of the path of totality, the inference would be fair that its apparent height was equal to or greater than the difference between the apparent diameters of the sun and moon. If, on the other hand, it was invisible at such point, then it would be fair to infer that its apparent height was less than the difference of tin- apparent diameters of the sun and moon. Whether it was indeed visible at any such point, I am not informed. At my station, no prominences \vciv seen above any portion of the moon's upper limb, while such prominences were visible at other stations, which fact indicated that my station was nearer the southern limit of the path of totality. There were several indications that the central line ol' totality was further north than the predicted place. So far as I have been able to compare, it would seem that the position of these prominences relatively to the sun's equator is within the same limits of distance as the spots on the sun's disk; and it is possible that some relation may be found to exist between the two classes of phenomena. With regard to the search for an intra-mercurial planet, the evidence so far seems merely neg- ative, and, considering all the difficulties necessarily attendant on the search, is by no means con- clusive against its existence. It is quite possible that this interesting question will yet be defi- nitely settled by new methods which were suggested while prosecuting the recent search. The clear atmosphere free from haziness gave the corona a well-defined, brilliant appearance, and altogether the circumstances were extremely favorable for witnessing this spectacle of beauty. The elevation of my station above tide-water, sixteen hundred and eighty feet, was estimated from the records of the survey of the Virginia and Tennessee Railway. Estimates of the latitude and longitude, as already stated, were based on those of the Coast Survey station : Latitude 36 35' 30" N. Longitude 5 9 W. Nothing further of importance is suggested by the memoranda of my observations. Very respectfully, your obedient servant, F. W. BAKDWELL, Aid. Commodore B. F. SANDS, U. S. N., Superintendent U. S. Naval Observatory, Washington, I), C. REPORT BREVET BRHI. GEN. ALBERT J. IYER, CHIEF SIGNAL OFFICER U. S. A. REPORT OF BREVET BRIG. GEN. ALBERT J. MYER, CHIEF SIGNAL OFFICER U. S. A. OFFICE OF THE CHIEF SIGNAL OFFICER, Washington. D. C., November 2, I860. COMMODORE: I avail myself with pleasure of the invitation extended iu your courteous note of the 1st instant to communicate to yon the details of observations made by me, in company with Colonel W. Wintlirop, also of the army, of the total eclipse of the sun on August 7, 1809, from the summit of White Top Mountain, near Abingdon, Virginia. Yon will please understand the word " observations" in its simplest colloquial sense, our expedition having been of the most informal and impromptu character ; and our only instruments two telescopes (not reversing) of a magnifying power (measured) of about forty-eight and four-tenths (48.4) diameters. With these we used, for solar observation, obscuring glasses or screens of plain red glass, thicknesses of which were added or taken away as occasion required greater or less obscuration. The point of observation, a mount- ain top, was sought with a view of placing ourselves as far as possible above the lower and denser strata of the atmosphere and the smoke, ha/e, and obstacles to vision with which they are charged. The extensive field of view was also desirable. The ascent of the mountain, which lies in the midst of a wilderness at the junction of the State lines of Virginia, Tennessee, and North Carolina, having been effected after a night's encampment in the woods and a somewhat severe inarch, early in the day an excellent position was selected, and the instruments were placed upon a flat rock on the open summit, from which was had a comprehensive view for fifty (50) miles, over billows of mount- ains, in near and distant ranges, and across the valley of the Holston to the westward. During all the morning, and until afternoon, the sky was wholly overcast witli thin white clouds, through which the sun's disk was dimly visible. At about 3 o'clock, however, a breeze sprang up from the northward, which, in the course of an hour, nearly cleared the western sky of clouds, so that a perfectly unobstructed view of the eclipse was had from the beginning to the end of the obscuration, and with the advantage that the effect of the changing light upon the masses of cloud near the apparent place of the sun, and elsewhere above the horizon, could be noted. Upon first turning the telescopes upon the sun, the spots upon its surface were noticed located as appears in the various photographs taken by other observers, which have doubtless been under your observation. The spot near the lower (southern) limb was the larger, and exhibited, as it seemed to us, a remarkably distinct penumbra. The first exterior contact was readily perceived, but no record of time was made. During the progress of the eclipse it was endeavored to observe whether there was change in the appearance of the spots on the sun as they were approached and then covered from view by the moon's disk ; and also whether, with glasses of the power used by us, any lunar prominences could be observed as projected against the disk of the sun as a background. The lunar limb did not exhibit, to our eyes, a sharply-defined or clear line, either as against the unobscured sun's disk or as covering the spots, but no prominences were noted. * The first strikingly remarkable accompaniment of the phenomenon which was observed was a flight of brilliant particles, seen by Colonel Winthrop, my companion, and described by him as a " shower of bright specks," to which he more than once called my attention while yet some four or five digits of the sun's disk remained uncovered, and which we do not doubt was the shower of meteors remarked upon by other observers. I was at the time using obscuring glasses too dense to permit the light of these meteors to be observed, a fact which has some bearing in reference to other observations made a few moments later. The next principal feature was one which I have, not perceived to have been yet recorded in the published reports of other parties. While some two digits of the sun's disk were still uueclipsed, and many seconds, perhaps a minute, before any appearance of the breaking of the visible sun cres- cent into Baily's Beads, there was distinctly seen by both my companion and myself, and verified 25* 194 REPORT OP BREVET BRIG. GENERAL ALBERT J. MYER. by attention mutually and repeatedly directed to it, a luminous cloud or prominence of a yellow line, upon the lunar limb below the solar crescent, and removed about fifteen or twenty degrees of the sun's apparent circumference from its lower extremity. It appeared as if from behind or attached to the moon's disk (southeastern portion) at this part of its circumference, of course showing an inky blackness. This object did not appear to be detached or floatiTig. It was fixed in its position and distinctly changed shape, either in itself or by movement of the moon's limb while under observa. tion. Its outlines were not sharp. An appearance, barely visible, was thought to be noticed at its northern and upper part, as might be of a thinner portion of the denser cloud drifting northward. No motion was perceptible. The whole prominence was carefully observed for some seconds. It must have been of a very considerable brilliancy to have been so distinctly seen while so much of the sun's disk was nnobscured, and to have been so plainly observed through the dense obscuring glasses then stilLiu use. It occurred tons, and it has been suggested by others, that it might have been one of the red or rose-colored prominences afterward visible during the totality, and now ear- lier observed under different circumstances of illumination, &c. If this be so, it would seem to establish that these protuberances emit a considerable light ; the observed cloudy prominence appearing distinctly luminous, either by its own, or reflected, or transmitted light; and more lumi- nous at its base, and near the moon's limb, than at its apex. As I now recall the eclipse, some of the red protuberances, and larger than this appeared, were at the moment of totality visible beyond the circumference of those portions of the sun's disk yet unobscured at the time of this observation. If these prominences possess such brilliancy, it would seem these ought, at this time, to have been also visible through the obscuring glasses. This would particularly apply to the prominence after- ward noted at about the center of the eastern limb, and that near the center of the northern limb. Xone were in view. This object did not answer to the description of a detached luminous point noticed by M. Laussedat, as observed at the lower extremity of the sun's cresent at the total eclipse of July 18, 18(50. It was further removed from the crescent, and though exhibiting through our colored (red) glasses light of the same appearance as that of the sun's disk, it was not so bright or intense. We were much impressed with the appearance at the time. Our limited experience did not permit us to account for it, and I am pleased to be able to submit the subject for more compe- tent consideration. Upon the breaking of the sun's crescent into the Baily's Beads, the crescent seemed to divide at first, at about the center, into two separate masses, each of which immediately parted into numerous fragments and then disappeared. At the moment of totality we ceased to use screens or obscuring glasses of any kind with the telescopes. Colonel Winthrop had been using hut a slight screen only for some moments before. The red prominences were at once visible. The telescopic appearance of the corona or aureola, during the totality, exhibited a clear, yel- lowish bright light closely surrounding the lunar disk and fading gradually, with perhaps some tinge of pinkish green, into the hue of the darkened sky. Upon this corona, extending beyond its brightest portion, the well defined rose-colored prominences were projected at various points of the circumference. They were larger in appearance and more distinct than we had been led to expect from such illustrations of total eclipses as we had seen. We observed no rose-colored clouds or objects appearing as detached from the sun's circumference, or as if floating in an atmosphere. Those visible to us gave the impression of attachment to the sun by their bases. They were of irregular conical shape. They showed steadily without any waving or flickering as of moving llame. and presented sharp outlines and an appearance suggestive at the time of their consisting of straight red rays something like such as are seen in the jet of flame springing from an ignited red light a pyrotechnic composition compressed in a tubular case. The exception to this steadi- ness was noted in the instances of the two central prominences of a number of four, observed a few instants only, on the western limb of the sun at the time the moon's disk was ceasing to obscure it. and almost simultaneously with the formation of the Baily's Beads upon this (western) limb at the moment of emersion. These seemed to incline, toward each other, and to leap for an instant into view as tongues of flame might do, and then were invisible at once. They were so instantly lost in the light of the unobscured sun that it could not be determined whether this was an actual motion or an optical effect, caused by the prominence's being visible but for an instant and then disappear- ing. The instan taneousness with which these red prominences disappeared at the moment of emer- OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 195 sioii would seem to show that the object first noted by us, before the totality, must have differed from them in something of composition or illumination. Of the red prominences, as now recollected, there were visible seven. One, and the largest, near the center of the lower (southern) limb, and one near the center of the eastern limb, were care- fully observed. One a little to the eastward of the center of the northern limb was noticed. Four were visible, for two or three seconds only, upon the western limb. That near the center of the lower limb was the larger and most attractive. Its size and position have suggested that it might be in some relation to the larger and lower spot upon the sun. All the prominences were similar and constant in hue, of a deep rose-color. To the unaided eye the eclipse presented, during the total obscuration, a vision magnificent beyond description. As a center stood the full and intensely black disk of the moon, surrounded by the aureola of a soft bright light, through which shot out as if from the circumference of the moon straight massive silvery rays, seeming distinct and separate from each other, to a distance of two or three diameters of the lunar disk; the whole spectacle showing as upon a background of diffused rose-colored light. This light was most intense and extended furthest at about the center of the lower limb, the position of the southern prominence. The silvery rays were longest and most prom- inent at four points of the circumference, two upon the upper and two upon the lower portion, appa- rently equidistant from each other, and at about the junctions of the quadrants, designated as " limbs," giving the spectacle a quadrilateral shape. The angles of the quadrangle were about oppo- site the northeastern, northwestern, southeastern and southwestern points of the disk. A banding of the rays, in some respects similar, has been noted as seen at the total eclipse of July 18, 1860. There was no motion of the rays; they seemed concentric. These discrete rays were not visible to me, or did not attract my attention with the telescope, and the diffused rose-colored light seemed to resolve itself in the field of the glass into the prominences. The field of the glass, with the whole disk in view, did not extend far beyond the prominences. My impression at the time was that the appearance of rays was due to some optical effect. The sight presented to the unaided eye was the superior in beauty; that through the glass in interest. This was so markedly the case that there was a sense of disappointment, on resorting to the telescope, at finding the size and beauty of the spectacle, as seen by the naked eye, so much reduced by the definition of the glass. The approach of the moon's shadow did not appear to be marked by any defined line, or the movement of any dark column of shade through the air. The darkness fell gradually, shrouding the mountain ranges and the dim world below in most impressive gloom. Our guides had been instructed to watch for the shadow as described, and to call to us at the glasses. They saw nothing of which to give notice. At the same time, and in vivid contrast, the clouds above the horizon were illuminated with a soft radiance; those towards the east with lights like those of a coming dawn, orange and rose prevailing; those northward and westward, as described to us by Mr. Charles Coale, of Abingdon, Virginia, who was present, with rainbow bands of light of varied hues. I quote, in his words, a description written by him, as of interest, in reference to the dispersion of light: " But the grandest of all to us, who had no astronomical ambition or astronomical knowledge to gratify, was the effect upon the clouds during the total obscuration. Those who have had the privilege of being upon White Top, and enjoying the westward scene, will remember the grand panoramic view of mountains beginning on the northern and southern horizon, and stretching away to the west till they seem to meet, will appreciate the scene that we now attempt to describe. Stretching along this semi-circle of mountains, in long horizontal lines, far below the sun, lay light and fleecy clouds as if resting upon their wings during the seeming struggle between the orbs above them. At the moment of the falling of the dark shadow, when naught was to be seen above but the stars and the circle of light around the moon, these clouds became arrayed in all colors of the rainbow, presenting an indescribable richness, with their background of somber mountain. To our vision it was as if bands of broad ribbon of every conceivable hue had been stretched in parallel lines half round the universe/' Our faces were not turned toward these, and we did not see them. No rainbow hues were seen before or after the eclipse. A very cursory examination only could be given the stars and planets visible during the totality, as in a clear twilight at evening. Venus and Mercury, near the apparent place of the sun, exhib- ited an unexpected brilliancy. Colonel Wiuthrop was impressed with the number of stars visible 196 REPORT OF BREVET BRIG. GENERAL ALBERT J. MYER. here and elsewhere in the heavens, and not confined to those of the first magnitude only, as by far greater than he had been led to anticipate by descriptions of previous eclipses. The fall of the temperature, already low at our elevation, was marked as the obscuration approached and reached totality. Our horses continued to feed quietly during the increasing dark ness, as at an approaching sunset. At the moment of emersion the first rays of the sun showed themselves at several detached points on its western limb, forming again the Baily's Beads, which united in a delicate crescent. It was a striking circumstance connected with the whole phenomenon that so many of its details could be observed with the unaided eye. In this manner our guides saw very readily Bai- ly's Beads, exclaiming that the sun was "breaking to pieces," and could distinguish without diffi- culty some of the protuberances. Much was no doubt due to the clearness of the atmosphere at so great an elevation. White Top Mountain has been measured by Professor Guyot, of JYinceton College, and found to be five thousand five hundred and thirty (5,530) feet above the level of the sea. He states it to be the highest mountain in Virginia, unless possibly its neighbor, Balsoni Mountain, which, however, is wooded to the summit, and would have been unstated to our purpose. If any interest can be attached to this informal narration, it will be because our party was one of the very few, possibly the only one, that observed successfully from a mountain top so elevated. It is to be regretted that the position was not occupied by observers better equipped and better qualified. I am, Commodore, very respectfully, your obedient servant, ALBERT ,1. MYER, Brevet Brigadier General and Chief /Signal Officer of the Ann;/. Commodore B. F. SANDS, U. S. N., Superintendent United States Naval Observatory, Washington, D. C. OFFICE OF THE CHIEF SIGNAL OFFICER, Washington, D. C., December 4, 1869. COMMODORE: I have the honor to transmit to you an extract from a letter just received from Mr. Charles B. Coale, of Abingdou, Virginia, in reply to a communication in which I requested more specific information in regard to the "rainbow hues" observed by him during the total eclipse of August 7, 1869, and to which reference was made in my report. I am, Commodore, very respectfully, your obedient servant, ALBERT J. MYER, Brevet Brigadier General and Chief Signal Officer of the Army. Commodore B. F. SANDS, U. S. N., Superintendent U. S. Naval Observatory, Washington, 1). C. ABINGDON, VIRGINIA, November 24, 1869. DEAR GENERAL : I have been absent from home seven weeks. In giving to the clouds "all the colors of the rainbow," I was probably bordering on the extravagant, though not more so than is allowable in country journalism. I distinctly remember, however, that there were distinct bands of pink, purple, yellow, orange, and fiery red, and each slightly tinged with different shades of its own color. One of the bands, I remember, had, to my vision, a slight lilac tinge. I do not remember to have observed any green or blue, but 1 do remember that the lower edge of the purple had a very faint blue tinge. All these resting against a dark background gave them an indescribably gorgeous appearance the lines of color seeming to be divided by strips of black. They all lay in horizontal lines, one above the other. My impression is that these colors appeared at the moment the shadow passed from the lower edge of the sun, though I am not positive. Having no astronomical knowledge or aspirations, and no instrument, my whole attention was directed to the clouds, and my whole soul absorbed in their indescribable grandeur. * Yours, very respectfully, CHS. B. COALE. General ALBERT J. MYER, TJ. S. A., Washington, D. C. REPORT PROFESSOE ASAPH HALL, TJ. S. N, REPORT OF PROFESSOR ASAPH HALL, U. S. UNITED STATES NAVAL OBSERVATORY, Washington, December 7, 1869. SIR: In accordance with thft order of the honorable Secretary of the Navy, dated May 3, 1869, I proceeded to New York, and having been joined there by Mr. Joseph A. Rogers, we took passage for San Francisco on the steamship of the 21st of May. At the request of Paymaster Eldridge, United States Navy, the officers of the Pacific Mail Steamship Company and of the Panama rail- road gave me letters of introduction to Captain Conner and to Captain Parker, of the steamships Henry Channcey and Colorado, and to the agents of the companies on the isthmus. To all these gentlemen we are indebted for good accommodations for the transportation of our chronometers and instruments and for a safe and pleasant journey. We reached San Francisco June 12, and the same day reported to Admiral Craven, at Mare Island navy yard. To Admiral Craven and the officers of the navy yard, and particularly to Captain Phelps, we are indebted for every assistance they could render us. Lieutenant Commander B. C. Merrhnan, in charge of the Navigation Office, furnished us with seven chronometers, a chronometer-case, and a barometer, for the expedition. After making obser- vations at Mare Island to determine the errors and approximate rates of the chronometers, on June 21 we went on board the United States steamer Mohican, Captain S. It. Franklin commanding, then lying in the harbor of San Francisco. We spent June 23 and 24 in making magnetic observations on the Island Ycrha Buena, and on June 29 the Mohican sailed for Plover Bay. This bay is 011 the northeastern coast of Siberia, in north latitude 64 20', and in longitude 6 1 ' 2o m west of Washington. The following reasons led to the selection of this place for observing the eclipse: the computed line of central eclipse passed only six or eight miles off the coast; an excellent harbor, easy of access, furnishes a secure anchorage for all kinds of vessels; and, from all the information I could obtain, the chance of having good weather is better there than on the American coast, and as good as at any point in those regions, near the line of central eclipse, that the short time remaining for the voyage would permit us to reach. Mr. William H. Ball, of the Smithsonian Institution, furnished me witli a map of Plover Bay and information concerning the natives of the country. We reached Plover Bay July 30, the vessel stopping on the way at Nanaimo, Vancouver Island, and at Una- laska. The next day Mr. Rogers and I ascended the mountains on the east side of the bay, hoping to find a suitable place for our observatory, but considering the difficulty and danger of carrying the instruments up and down the steep mountain trails and the necessity of frequently comparing the chronometers on the ship, we decided to locate our observatory on the sand spit at the lower anchorage. This enabled us immediately to begin observations for time and latitude, and to finish our magnetic observations before the day of the eclipse. On August 1 Mr. Carter, the carpenter of the Mohican, put up our observatory on the sand spit, and our instruments and bedding were transferred from the ship in Emma Harbor to the observatory, a distance of about six miles. On unpacking the instruments we found them in good order, not one having been broken or injured on the voyage. We left Plover Bay at midnight, August 7, and reached San Francisco September 21, stopping, on our return, at Esquimalt, Vancouver Island. To Captain S. R. Franklin, United States Navy, and to the officers and men of the Mohican, we are indebted for the successful termination of this long and difficult voyage, and we offer them our hearty thanks for their uniform kindness to us. 200 REPORT OF PROFESSOR HALL. THE ECLIPSE. The subjoined sketch of the country around Plover Bay shows the positions of our observing stations and of the ship in Emma Harbor. We thought it best to observe the eclipse from different stations, hoping that, in case of cloudy weather, some of the ob- servers might in this way obtain observations. In order to ascer- tain if it were practicable to take instruments to the top of the mountains near the coast, on Au- gust 5 Mr. Eogers, accompanied by Mr. liichard Baker, made an excursion from the ship down the valley to Lake Moore. They as- cended Bald Head and went down the west side of the mountain to Plover Bay. I am indebted to Captain P. S. Itedfield, of the whaling brig Victoria, of San Francisco, who furnished me with a five-oared whale-boat, a crew of five Indians, and Mr. W. E. AVhite as boat-steerer. On the evening of August 6 I went in this boat to the Indian village on East Head, remained there over night, and in the morning ascended Bald Head, accompanied by Mr. White and ten Indians, who carried the instruments. This mountain is the second peak from the sea, and is very nearly in the meridian of our observatory on the sand spit, and about three miles south of the observatory. During the night of August the sky was perfectly clear, and a cool wind from the north promised a continuance of good weather. About an hour before the beginning of the eclipse low cumulus clouds drifted rapidly from the west over the sky. As the clouds passed toward the east the partial eclipse was occasionally seen through the openings. On the approach of the total eclipse everything became hushed and still: the sea-birds stopped their Mights and the Indians huddled together in awe. As the shadow passed over the mountain the effect was startling. In the stillness and darkness of the moment it seemed as though all life had been swept from the earth. The fearful gloom of total eclipse was increased by the desolate appearance of the country, without tree or shrub, or anything pleasant to the eye. Near the horizon a belt of clear sky, fifteen or twenty degrees in altitude, became of a ruddy color, like the evening sky after sunset in autumn. At the same time the lower portions of the clouds toward the north and east were of a dull white or ashy appearance. I could see nothing of the protuberances, and had only at times an indistinct view of the corona. During the totality I was able to read the face of my chronometer without the aid of the lamp. The clouds were apparently denser toward the sea-coast, and prevented me from obtaining accurate observations of the times of contacts. Within an hour after the end of the eclipse the clouds had entirely. disappeared, and all that long afternoon the sky was cloudless. The times that I observed are the following: /;. in. a. Beginning of total eclipse 4 5 uncertain, End of total eclipse 49 very doubtful, with pocket chronometer Dent 7986. the power employed was 42. The telescope used by me has an aperture of 3 inches, and 1869. 201 The following are the accounts of Mr. Eogers and Mr. Very, who observed on the sand spit in Plover Bay : DESCRIPTION OF THE ECLIPSE BY MR. ROGERS. "The night before the eclipse was perfectly clear, and I continued to make observations for time during the whole of the short period in which stars were visible with the small telescope of the portable transit. An hour or two before the beginning of the eclipse clouds appeared in the northwest, and rising rapidly soon obscured the sun. About this time Mr. S. W. Very, navigator of the Mohican, arrived from the ship, bringing M. T. chronometer Negus 1097, from which the times recorded below were taken. The observations were made at the observatory on the spit, with the telescope loaned by the University of Pennsylvania. The smaller telescope belonging to the United States Naval Observatory, and sidereal chronometer Negus 1276, were used by Mr. Very a few yards distant from my position. " At the predicted time of first contact the greater part of the sky was covered with clouds, and the experience of the preceding week gave little reason to hope that they would be soon dispersed. They were not quite continuous, however, nor dense enough to prevent the sun's position from being- pretty plainly indicated even when it was quite invisible. " When first seen through one of the openings, the moon's limb had already covered a consider- able portion of its disk. It was several times visible for a few seconds during the partial phase, but some time was necessarily lost in bringing it into the field of the telescope, and I was unable to note the occultation of any of the spots. As the time of total phase approached the light gradu- ally diminished. The sun appeared for an instant through the clouds as a slender wire-like crescent; and a few seconds later its obscuration was evidently complete. Except a slight moaning of the wind at intervals, there was no sound but that of the sea on the beach and the beat of the chro- nometer; and the silence and gloom strongly resembled that which sometimes precedes a thunder- storm. The sky in the southwest above the sea horizon was of a deep orange color, while in all other directions the outlines of the mountains surrounding the bay were just discernible. "The darkness was not so intense as I had anticipated ; but there was apparently much less light than the twilight of the preceding midnight. I had taken the precaution to illuminate the face of my chronometer by artificial light, and thought it would not have been possible to distinguish the numerals on the dial without it. The progressive diminution of light appeared to cease at 9 h 17 m 30 s ; and at 9 h 20 m s a rapid increase of light began. This interval is less than the duration of total phase, and seems to indicate a very plainly perceptible variation of the illumination during totality; though it may have been partly owing to changes in the density of the clouds. " At 9' 1 21 s the clouds parted for a few moments and showed the emerging limb of the sun as a narrow crescent. Toward the end of the eclipse it was again visible for a short time, during which I observed the complete emersion of the umbra of a large spot near the eastern limb at 10 h 23"' 0".r>. The apparent position of this spot, as seen with the telescope at ll h O m , is shown at S in the annexed diagram. At 10 h 20"' 57 S .5 another glimpse of the disk was obtained, which then presented an unbroken circular outline. " The thermometer in the early part of the eclipse had indicated 46 Fahrenheit. During total obscuration it fell to 42, and afterward rose gradually to 60 at the end of the eclipse. These temperatures were noted by Mr. R. Barker, captain's clerk of the Mohican. , " The clouds which had already begun to disperse soon disap- APPEARANCE OF THE SPOT AT 1 1 ' o " peared entirely, and the remainder of the day was clear and warm. "JOSEPH A. ROGERS." 26* 202 REPORT OF PROFESSOR HALL. ME. VERY'S LETTEE. " UNITED STATES STEAMER MOHICAN, (third rate,) " Off Cape Tchukotski, Siberia, Aiji<xt 8, 1869. " SIR : I was unable to make auy accurate observations of the total eclipse of the 7th iustiint. The times of first contact and total phase were lost on account of the clouds, but the time of egress I obtained within two seconds after it occurred. By chronometer Negus 1276, (sidereal,) it was 2 h 28 41 s . " The following are the comparisons made during the day : " About 5 a. in., before leaving the ship " Chronometer Negus 1316, (standard,) 4 h 49 30 8 .0 50 00 8 .0 50 30 s .O (Mean time.) " Chronometer Negus 1097, 4 h 50 m 23 8 .5 -50 53 8 .5 51 23 8 .5 (Mean time.) " About 8 a. in. before observing " Chronometer Negus 1097, 7 h 41 00 8 .0 43 m 30 8 -0 (Mean time.) " Chronometer Negus 1276, ll h 43 52 8 .5 46 m 23 8 .0 (Sidereal.) " About 11 a. m. after observing " Chronometer Negus 1097, 10 h 30 09 S .5 33 m 09 8 .0 (Mean time.) " Chronometer Negus 1276, 2 h 33 30 s .O 36 30 s .O (Sidereal.) " Very respectfully, "SAMUEL W. VEEY, "Master and Navigator.'" The telescope used by Mr. Very has an aperture of 2| inches. I am indebted to Captain Franklin for the following account of the eclipse se'en from the ship in Emma Harbor : " UNITED STATES STEAMER MOHICAN, (third rate,) " Plover Bay, Siberia, August 7, 1869. "DEAR SIR: As you expressed a desire to get all the information possible in connection witli the eclipse of the 7th of August, and wished me to give you the benefit of what came under my observation at the time, it gives me much pleasure to furnish you with a copy of a few notes I then made. "The eclipse commenced about 8.40 a. m., local mean time, on the right upper edge of the sun ; and although the weather was cloudy, we were enabled from time to time to get a glimpse of it through the openings in the clouds, and thus mark its course as it advanced. " At about 9.45 the darkness became very apparent, and before the sun was entirely obscured the sea birds around us had gone to roost. The darkness came upon us very suddenly, the clouds opposite the sun, from having been a light ashy color, became suddenly black as the blackest storm clouds; those under the sun and in the direction of the Arctic Sea assumed a whitish hue, which might have been produced by the reflection from the snow and ice of that region, while those to seaward took up an orange and yellowish tint. The sea assumed the color of the deepest indigo, and the whole scene, in its effects upon the sky, and sea, and surrounding hills, was sublime beyond anything of which I can convey an idea ; nothing could present to the mind a picture of more utter desolation. There was but one star* visible, owing to the overcast condition of the sky. The flames of the sun were distinctly visible, and three fiery lumps could be observed on the edge of the moon during the totality, resembling molten iron. The darkness, which continued for a few moments, was not complete, and passed away as suddenly as it came, indeed, it seemed to me that the transition from darkness to light was more rapid than that from light to darkness. Soon every thing resumed the appearance it had before the totality, and the eclipse finished at 10 b 27 45 s by standard chronometer. " I am, very respectfully, your obedient servant, "S. E. FRANKLIN, " Commander United States Navy. "Professor ASAPH HALL, United States Navy." "Mercury. A. II. OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 203 At the ship, Mr. Inch, chief engineer of the Mohican, and Mr. Wainwright, ensign United States Navy, observed the times of beginning and end of the total eclipse, but unfortunately their notes and comparisons with our chronometer were lost. Their observed duration of totality was 3'" s . Collecting the times observed and applying the correction of the chronometers, we have the following results : Station. Phase. Chronometer. Obs. Time. Corr. Chron. Local M. T. Notes. Obs'r. . h. m. s. h. m. s. h. m. s. Bald Head . . . Bog. totality Dent 7986 . 450. - 6 21 15. 21 43 45.0 Uncertain . H. Sand Spit . . . Beg. totality Negus 1097 . 9 17 30. 11 32 49. 3 21 44 40. 7 Uncertain . R. Sand Spit . . . Spot . . . Negus 1097 . 10 23 fr. 5 11 32 49. 3 22 50 11. 5 Good . . R. Sand Spit . . . . " . Negus 1097 . 10 26 57. 5 - 11 32 49.3 22 54 8.2 . . . . E. Sand Spit . Last contact Negus 1276 . 2 28 41. 6 30 15. 3 22 52 32. . . . . V. Ship . . . Last contact Negus 1316 . 10 27 45. 11 30 55.8 22 56 49.2 F. Iii making these reductions I have assumed that Bald Head is in the meridian of the observa- tory on the sand spit, and that the ship was one minute east of the observatory. The position of the ship can be found from the triangulation of the bay made by Mr. Yery. With regard to the eclipse, I most sincerely regret that we had no means of taking photo- graphs. As the weather happened to be, this was the one thing most needful for us, and I hope that our fortune in this respect may be a warning to future expeditions. DETEKMINATION OF TIME, LATITUDE, AND LONGITUDE. 1. The observations for time were made with a small portable transit instrument belonging to the United States Coast Survey, and lent for the occasion by Professor Peirce, the Superintendent. This instrument has an axis thirteen inches in length and an object-glass of 1 T 7 B inch aperture. The magnifying power is 17. On first setting up the instrument we found a large error of collimation, and in attempting to make the adjustment the head of one of the adjusting screws twisted off. To supply the place of the screw a spring was inserted by Mr. Eogers and used throughout the obser- vations. At Mare Island the transit was mounted in the small observatory erected for Captain Brooke in 1859. The stone pier having been displaced, we reset it and bolted a two-inch oak plank carrying the supports of the transit to this pier. The observations were made with the sidereal chronometer Negus 1270, and by the eye and ear method. The instrument was reversed in each series of observations. The level was read as often as once in twenty minutes. Before beginning observations the errors of level and collimation were adjusted, if necessary, and then no further adjustments made during the night. The observations have been reduced in the following manner. The observed time of transit over each of the seven wires was reduced to the middle wire by means of the equatorial intervals, and the corrections for level, daily aberration, and rate of chronometer were applied to the mean of the seven reduced transits. A comparison with the Ephemeris gave an approximate value of the correction of chronometer. A value of this correction was then assumed and equations of condition formed in the usual manner. The solution of these equations gave the azimuth and collimation errors and the final correction of the chronometer. The following are the approximate values of the correction of the chronometer obtained from each star : 204 EEPOET OF PROFESSOR HALL. MARE ISLAND. JUNE 17, 1869 .... Observer, Rogers. JUNE 19, 1869 .... Observer, Rogers. Star. Approx. Corr. Wires. Circle. Star. Approx. Corr. \Viiv*. Circle. h. m. s. ft. m. s. Polaris, S. P. . . 3 4 0.87 3 W. Polaris, S. P. . . 3 4 6.06 2 E. a Virginis . . . 4 35.95 7 W. 71 Bootis .... 4 40.81 7 E. )/ Ursa' Majoris . . 4 37.39 5 HE. a Draconis . '. 4 42.30 5 K. a Draconis ... 4 40.85 7 E. a Bootis * .... 4 40. 46 7 E. a Bootis .... 4 37.53 7 E. 6 Bootis .... 4 40.39 3 E. Bootis .... 4 38.32 6 E. e Bootis .... 4 40.08 7 E. e Bootis .... 4 37.42 7 E. /? Ursae Miiioris . 4 41.73 7 E. a 2 Librae .... 4 37.60 6 E. a 2 Libra? .... 4 41. 15 2 E. /3 Ursoe Minoris 4 41. 49 5 E. (3 Libra? .... 4 38.71 6 W. /3 Librae .... 4 35.61 7 W. y 2 Ursa) Minoris . . 4 39.33 6 W. y Ursas Minoris . 4 37.29 7 W. o Serpeutis . . . 4 40.10 7 W. a Coronas Borealis . 4 36.35 7 W. a Serpentis . . . 4 36.23 7 W. JUNE 18 ..... Observer, Hall. JUNE 20- Obscmr, Hall. Polaris, S. P. . . 34 29.04 3 E. Polaris, S. P. . . 3 4 21.84 2 W. o Virginis ... 4 39.53 7 E. a Virgiuis ... 4 41.25 7 W. T] Bootis .... 4 39.26 7 E. ri Bootis .... 4 42.97 7 W. a Draconis . . . 4 39.51 7 W. a Draconis . . . 4 43.44 2 W. a Bootis .... 4 39.22 7 W. a Bootis .... 4 42.59 7 W. 6 Bootis .... 4 40.69 7 W. e Bootis .... 4 41. 12 6 E. e Bootis .... 4 39.48 7 W. Clouds. a* Librae .... 4 39.50 7 W. /I Ursa? Minoris . . 4 38.74 6 W. /? Librse .... 4 38.73 7 E. y 3 Ursa; Miuoris . 4 37.64 7 E. a Coronas Borealis . 4 38.52 7 E. a Serpentis . . . 4 38.31 7 E. SEPTEMBER 28 .... Observer, Hall. SEPTEMBER 29 ... Observer, Rogers. <5 Draconis 37 17.70 7 W. j8 Lyrao .... 3 7 19.58 7 W. S Aquilse .... 7 18.41 7 W. f Aquila? .... 7 18.38 7 W. K Aquilae .... 7 18.48 7 W. 6 Draconis 7 16.37 7 W. y Aquilse .... 7 18.22 7 W. S Aquilae .... 7 19.14 7 W. a 'Aquilse .... 7 18.05 7 W. 7 Aquilao .... 7 20. 47 7 E. (3 Aquilse .... 7 18.35 7 W. a Aquilse .... 7 20.39 7 E. v Capricorni . . . 7 17.29 7 E. f) Aquila? .... 7 20.65 7 E. K Cephei .... 7 11.45 1 E. K Cephei .... 7 15.95 7 E. a Cygni .... 7 15.35 7 E. e Delphini . . . 7 20. 42 7 E. It Aquarii .... 7 17.05 6 E. v Cygni .... 7 15.94 5 E. At Plover Bay the transit instrument was mounted on a wooden pier filled with sand. A cover for the pier was made of pine boards fastened together with wrought nails, and the o;ik plank was secured to this cover by a bolt. The weather was so unfavorable that no observations could be OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 205 made before the night of August 5, when the sky suddenly became partially elear. A few obser- vations were made, but before any could be made in the reversed position of the instrument the sky became overcast. On examining the instrument the collimation error was found to be large, and as there was no way of determining it, the observations of the 5th could not be reduced. On the evening of the Oth the instrument was brought nearly into the plane of the meridian, the collima- tion and level errors adjusted, and no further adjustments attempted during the night. The reduc- tions have been made as before, save that here an approximate value of the azimuth correction was determined, and this correction has been applied to the results given below. PLOVEli BAY. AUGUST 6, 1869 Olwrm; Rogers. Star. Approx. Corr. Wires. Circle. h. m. s. y Draconis 6 30 14.82 6 W. 30 14 62 7 W 8 Lvr:i- 30 14 80 3 W f AquiliD 30 13.96 6 W. 30 14 76 5 W a Cy r !ii 30 14 24 7 W a Cephei 30 16. 10 7 W. 30 13 99 6 E a Aquarii 30 15 02 7 E C IVjjasi 30 14. 93 7 E. a IVgasi 30 14. 44 7 E. These observations give the following corrections of the chronometer Negus 1276 : Mare Island, June 17, 18, 19, 20, Mare Island, Sept. 28, 29, Plover Bay, Aug. 6, Sextant observations for time were made at Plover Bay on August 3d and 4th. These observa- tions have been used only as a control, and I have preferred to depend on the transit observations for time and longitude. The following are the results. The pocket chronometer Dent 7986 was used in all the sextant observations. Chron. time. h. m. S. 8. Observer. 17>>. 5 3 4 37. 29 0.15 B. 17". 5 3 ' 4 39. 140.15 H. 17 h . 5 3 4 40. 100. 17 E. 17 U . 5 3 4 41. 92 0.20 H. 23\ 3 7 16. 98 0.05 H. 23 h . 3 7 19. 12 0.14 B. 3\ 6 30 14. 59 0.17 E. Date. Chron. Time. Correction of Chron. Interpolated Corr. No. Alts. Observer. ft. h. m. s. s. h. m. s. Aug. 3, a. m. 2.63 - 6 21 52.3 1.37 6 21 53.6 12 H. Aug. 4, a. m. 2.65 . - 6 21 45.7 0.52 6 21 45.3 15 H. Aug. 4, p. m. 8.92 - 6 21 40.6 1.29 6 21 41.8 15 R. Aug. 4, p. m. 9.70 - 6 21 40.8 0.56 6 21 41.1 16 R. The chronometer Dent 7986 was compared with the sidereal chronometer immediately before and after observing, and" column 4 gives the correction deduced from these comparisons, the correction of the sidereal chronometer having been found by means of its daily rate from the transit observa- tions of August 6. If we observe altitudes near the prime vertical, the difficulty of determining the time will increase very nearly as the cosine of the latitude diminishes, and in high latitudes the determination becomes 206 REPORT OF PROFESSOR HALL. uncertain. Prom all the observations, 58 altitudes, I find the probable error of the time determined by a single altitude to be 3 8 .40. As an example of our work, I give here the observation of August 4, a. in. : Chronometer. Double Alt. Corr. Chron. Ti. m. . O I II h. m. s. 1 54 28.4 48 58 30 6 27 33. 3 (1) Index Corr = + 38.7 56 48.6 49 27 30 27 35.2 57 29.5 49 36 40 27 32.3 (2) Index Corr + 33. 8 Clouds. A new series. 2 39 2.8 59 10 50 27 30.4 Adopted -f- 36 2 39 50.4 59 20 27 31. 6 o 40 19. 59 26 27 30.2 Thermometer . . . . 52. 5 40 58.8 58 30 40 27 40.0 Barometer 29 61 41 43.0 58 40 27 27.0 A. Thermometer . . . 52. 2 42 17. 6 58 46 10 27 30. 4 43 32.0 59 30 27 32.8 Reversed horizon. 44 23.2 59 11 10 27 29.0 44 58.5 59 17 50 27 30.5 46 0.5 60 32 40 27 32.9 46 40.8 60 41 27 30.8 47 20.8 60 48 40 27 31.5 Mean = 6 27 31. 86 2. The observations for latitude were made with the Pistor & Martins patent sextant, No. 107. This sextant belongs to the Naval Academy, and was procured for us by Professor Coffin. As both of the observers were inexperienced in the use of a sextant, and being desirous to know the quality of the work done by such an instrument in su<5h hands, I have computed the latitude from each observed altitude. The observations were made in sets of twelve and sixteen altitudes, taken when the sun was near the meridian. They were made symmetrical with respect to the limbs of the sun and the cover of the horizon, although interruptions by clouds sometimes prevented this from being done completely. August 3. Observer, Rogers. August 3. Observer, Rogers. 23 47 21 59 22 23 22 30 22 23 22 26 22 30 22 18 22 20 22 24 22 25 22 16 22 28 22 18 22 24 22 24 = +64 22 14 22 17 22 27 22 20 22 20 22 23 22 22 22 17 22 19 22 28 22 10 22 35 22 4 22 47 clouds 64 22 22 1". 3 64 22 22 1". 9 OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 207 I have rejected the first altitude measured in which there appears to be an error in reading the chronometer or sextant. The probable error of the latitude from a single altitude is 6".l. August 4. Observer, Hall. August 5. Observer, Hall. August 5, Observer, Hall. o i if o / n o i ii <f = +61 22 40 <f= +64 22 14 <p = +64 22 41 22 30 22 35 22 29 22 3 22 37 22 29 22 27 22 27 22 33 22 36 22 9 22 25 22 38 22 32 22 11 22 46 22 37 22 20. 22 40 22 31 21 55 22 26 22 20 22 5 22 27 22 28 22 1 22 39 22 38 22 24 22 50 22 21 22 21 22 18 22 38 22 20 22 39 22 32 64 22 33 1".9 64 22 27 1".9 64 22 20 2".7 The probable error of the latitude from a single altitude is 7".8. Taking the mean of the several results without regard to the probable errors, the latitude given by the sextant is <? = + 04 22' 25". 3. For the determination of longitude ten chronometers were used. A box was fastened to the floor of the ship's cabin, and in this the case for the chronometers was securely fixed. The chro- nometers were wound and compared daily at about 9 o'clock a. m., and the temperature of the box was observed generally three times a day, at 9Ja. m., 2J p. m., and at 9 p. m. The temper- ature to which the chronometers were exposed was quite uniform, and until September 21 the extremes of the observed temperatures are 44 and 64. After our return and while lying in the harbor of San Francisco, the temperature rose to 75, anil this increase appeared to produce small changes in the rates of some of the chronometers, but these changes are so small and occur so near the end of the voyage that they will not, I think, seriously affect the determination of longitude. The ship's 9-inch gun's and 24-pound howitzers were fired a few times on July C, and all of her guns were fired repeatedly September 20. The firing of July 6 produced no change of rate that could be detected, and neither did that of September 20, unless the small changes spoken of above and ascribed to an increase of temperature were produced in this way. Two excellent chronometers were furnished us by the Messrs. Negus, of New York, Nos. 1097 and 1316, of their own make, and No. 1316 was chosen as our standard chronometer with which the others were compared. At Mare Island, through the kindness of Lieutenant Commander Merriman, we procured seven additional chronometers. In the daily comparison the chronometers were com- pared in the order in which they are placed below, beginning with Negus 1276, and ending with Negus 1298, the interval between the comparison of two chronometers being one minute. As the sidereal chronometer Negus 1276 was taken out of the ship for the purpose of observing, the times of comparison are not so uniform with it as with the others. The chronometers were Negus 1316 Negus 1097 Negus 599 Negus 1287 Negus 1317 Negus 1276 Dent 2118 Negus 772 Desilva 694 Negus 1298 208 REPORT OF PROFESSOR HALL. I _fl I u bo a "S as 1 TH I a o a o rH I So 02 r? I PH a O -r=> 3 a; a I cs to . s a* o a , 8 rH CO r i s S S r: a a -T CO in S ~- Ml to S rr. s S to fe to rH S O to CO ^. -r -r r- m ^ to TH rH o to o 00 OS 13 " ?? CO s SB 4r -C o -* m S rH in 00 O H 7) rH T-t O3 7) to IN J 1 o t. ^ o CO CO TH GO * to 00 = O 99 CO t cn rH JDent 2118 of 1316 S co r IN 7' 3 -r 1C 3 3 1C ,-: -T *r s fc ~ _ -r in S CD rH - -r E o -T -T J <N m CO -T ; 9 to to S3S to IN o o CO rH o I, -r -r I- CO 1C te O5 to CO as CO 00 n || CO S co a 00 a a 71 S 9? 9? CN a ^ g 7) oo CO rH Si 71 in 7) M r: -T -r T~ m rf -r T 1C CO ^=2 - gs ^ 00 00 o CO <jl o o m CM _ CO 00 O 1C to CO I, 00 OS * in -r " rH H 9) in O( S r. t 7> 00 S_t 17 CO ~ d to _. CJ | S ^ 8 7! 7'' s *} SI *} c* 71 ri 7) 71 71 7.' 7) 71 <N <N feS rH rH 00 CO to t. to t. TH 00 rH CO to <N m O CO to * O C3 TH TH ^ " S S rH 8 8 00 rH 3> 7=, 99 fe Oi S CO to ?' -T 00 CO | O rH o -r rH H y? .7 - '- b II rS '"' ^53 US to 00 (N r. 0> o o 00 OS (N 00 C O 00 O> CO O 00 CO CjrH in IH l> t* - -r 00 7> 77 ffj ~ OS C7 / 7> -C r ^ 7t 00 00 S o p* ^* -r -* g m 17 -T g --i te g I- ^ i- t* j. / X / OS ft I to rH IN c* <N c-. ^ ^ CD ~ CO m (N 00 O (N o = CO O5 CO 00 TH TH CO ' ti * S' m (N -r m -.0 rH S IN ' S if. - rH CO CO 2 CO i? CO <N $ S o CO 1C op CO 00 w IN CO I o co 00 in 09 CO in rH 00 00 CO TH to m TH <N a CO m OS 11 TH O OS m SS rH 17 IN 17 IN ^ CO Si CO CO o -t. 1 CO m m ' m m to -r m CO to TH to C7 to s IB s rH I- s? 1 IN to in s ^ 1 ~ -r CO I I -r I i 00 1 I 1 i 00 1 1 I i 1 1 Is TH s 1-3 -7 M s -T r-l 5 1-5 X CO rH 00 rH V 00 IN (N ii 7> r. rH S E5 rH t <2 T 1 T -; (N , coco *^ OS to in (M IN 1C * m rH o IN 01 ^- OS m t- t> m s rH rH OJ<H " in g 9 -a m rH % rH 00 m rH 09 "T CO (N CO 71 (N -r in CO 00 IN CO .7 CO to 77 <N '.'. ^T CO m m CO m CO CO M CD (N CO -r to s 00 1 CO 1 | 1 | 1 I ^7 K ^-~ 99 -r 1 I CO CO 9 i 7 s e S -f -* CO O TH 9 S 1-3 S 01 | 00 '.-. /. i~ S ir. 3 7> T 1 02 to ^ " s OBSERVATIONS OP THE ECLIPSE OF AUGUST 7, 1869. 209 In the preceding- table the first column of dates gives the times of the comparisons of the sidereal chronometer Negus 1276, the second column the times of the comparisons of Negus 1298. I have now assumed a constant rate for each chronometer, and with these rates have computed for each date the difference between the standard chronometer and each of the chronometers. Subtracting the observed difference from the computed, I find a series of residuals, the mean of which for each date is assumed to be the correction of the standard chronometer. Subtracting the correction of the standard chronometer from the first residuals, we have the following table : Negus 1276. Negus 1097. Dent 2118. Negus 599. Negus 772. Negus 1287. Desilva 694. Negus 1317. Negus 1298. Negus 1316. 8. 8. s. a. 8. 8. 8. 8. 8. 8. 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 + 0.9 + 3.3 1.3 + 4.1 1.5 + 0.8 3.2 2.8 0.3 0.2 0.2 + 5.2 - 2.4 + 8.2 3.6 0.3 6.1 + 0.7 - 1.7 1.3 1.5 + 5.7 2.9 + 10.2 - 4.9 1.0 9.3 + 5.3 1.8 1.5 0.8 + 7.1 - 2.6 + 11.9 5.4 0.8 9.6 + 2.1 1.5 0.8 - 0.1 + 9.0 3.2 + 12.2 5.7 0.2 9.6 0.8 - 1.3 - 0.4 + 0.6 + 10.3 2.3 + 8.3 3.5 + 0.8 6.6 - 6.6 1.1 + 0.9 + 1.4 + 10.0 - 2.0 + 5.4 0.6 0.6 - 4.5 - 9.7 0.2 + 2.3 + 0.5 + 9.7 2.2 + 4.9 + 0.6 + 0.1 1.9 10.8 0.7 + 2.0 1.0 + 8.9 1.9 + 0.1 + 1.8 0.3 + 3.5 - 11.5 1.2 + 2.4 + 1.6 + 6.9 1.5 1.7 + 3.5 0.5 + 5.2 - 11.0 0.9 + 1.2 + 1.2 + 5.9 0.8 3.7 + 4.4 1.6 + 5.8 9.0 2.5 + 1.2 + 0.6 + 5.5 1.7 6.6 + 5.6 1.3 + 5.8 5.3 3.0 + 1.3 + 1.0 + 4.3 1.5 - 9.4 + 7.1 + 0.1 + 6.4 - 6.4 - 1.8 + 2.4 0.3 + . r >. :i + 0.5 11.7 + 7.3 + 1.6 + 8.6 - 11.0 0.2 + 3.2 + 1.4 + 5.3 + 1.1 - 10.9 + 5.5 + 1.3 + 8.6 - 12.6 + 0.2 + 2.5 + 0.9 + 5.1 + 1.8 - 10.2 + 3.2 + 1.3 + 7.2 9.2 0.0 + 1.6 + 0.5 + 4.0 + 0.7 5.4 + 1.9 + 1.0 + 5.2 - 7.5 0.6 + 0.4 + 0.7 + 3.6 + 0.3 - 10.4 + 4.3 + 0.7 + 4.4 3.5 + 0.2 + 1.7 + 1.0 + 1.7 0.3 - 10.4 + 4.0 + 0.4 + 3.4 0.5 + 0.4 + 1.9 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 In order to determine the relative values of the longitudes given by the chronometers, it is necessary to banish from these residuals all law of sign. Without attempting to do this rigorously, or to introduce a coefficient depending directly on the temperature, it is sufficient for our purpose to assume a simple function of the time. If, therefore, the whole interval of time be represented by a semi-circle, I find the following expressions for the rates: Negus 1316, daily rate Negus 1276, daily rate Negus 1097, daily rate Dent 2118, daily rate Negus 599, daily rate Negus 772, daily rate Negus 1287, daily rate Desilva 694, daily rate Negus 1317, daily rate Negus 1298, daily rate The probable errors are those of a single 27* = 1.178 1.4 sin t 0.8 = +1.554 0.7 = _o.641 7.2 sin t 1.4 = +7.337+ 1.5 sin t 1.0 = +3.49211.6 sin 2 t 1.8 = 0.691+ 5.0 sin 2 t =t 1.7 = +5.062 0.6 = +1.746+ 9.0 sin 2 t 2.1 = +8.078+ 9.0 sin t 3.0 = +2.297+ 1.9 sin t 0.7 interpolated value. 210 REPORT OF PROFESSOR HALL. From the observations and comparisons at Mitre Island we have the following corrections of the standard chronometer Negus 1316 : It. m. s. Observer. June 17.78C6 8 835.76 E. 18. 7689 35. 22 H. 19. 7735 33. 86 E. 20. 7189 32. 96 H. Mean, June September 19.2620 8 8 3445 28.6456 8 6 34.48 29.6336 34.31 H. E. Mean, September 29.1396 8 634.40 By means of the comparisons of the chronometers and the above values of the rates, we have the following corrections on local time, and the values of the longitude of Plover Bay referred to Mare Island : Chronom- eter. Mare Island, June 19. 2646. Reduction for rate. Mare Island, August 7. 9851. Plover Bay, August 7. 98)1. Longitude. Ti. m. s. m. s. Ik. m. s. h. m. s. It. m. s. 1316 8 8 34. 4 + 1 0.0 8 7 34.4 11 31 55.7 + 3 24 21. 3 1276 3 4 39.7 1 17.3 3 5 57.0 6 30 16. 1 24 19.1 1097 8 9 7. 6 + 39. 1 8 8 28. 5 11 32 49. 8 24 21. 3 2118 10 41 8. 6 6.3 - 10 47 14. 3 14 11 35.3 24 21. 599 8 46 18. 1 2 53.6 8 49 11.7 12 13 34.4 24 22. 7 772 7 46 18.7 + 34. 4 7 45 44.3 11 10 6.5 24 22.2 1287 9 26 2. 6 4 11.7 9 30 14. 3 12 54 36. 8 24 22.5 694 8 52 59. 9 1 26.8 8 54 17. 7 12 18 42. 6 24 15.9 1317 10 33 34. 6 6 50.6 - 10 40 25. 2 14 4 48.2 24 23.0 1298 8 10 34.2 1 56.1 8 12 30. 3 11 36 51. 4 24 21. 1 Taking the mean of these determinations according to the weights indicated by the probable errors, and considering the probable errors of the local times, we have + 3h 24^ 2 i 8 .i (K36 as the longitude of our observatory at Plover Bay from Mare Island. The longitude of Mare Island has been assumed as +8 h 9m 1 8 .0 from Greenwich, or +3 U O m 49.0 from Washington. The longitudes of all points on our western coast are referred to San Francisco as a standard point, and the longitude of San Francisco has been deduced from the observations of moon culminations. For the present I take as the longitude of Plover Bay from Washington +6 b 25m 10M The following observations of latitude were made July 24 at Illiouliouk, on the Island Una- laska. The observing station is at the sun-dial erected by the Eussian Fur Company, and is about eighty yards very nearly north of the west end of the Greek church. The longitude has been assumed to be 5 h 57 m 47 8 .4 west of Washington. On account of cloudy weather, no observations could be made for time, and those for latitude were made through light clouds. Each value of the latitude has been computed from the mean of five observed contacts. OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 211 HltouUouk. Q I II July 24, I860, <p= + 53 52 60 ,52 58 52 50 52 39 52 36 52 27 52 37 52 39 52 31 52 26 52 19 y, = + 53 52 382".7 At Esquimalt, Vancouver Island, sextant observations were made for time and latitude, and through the kind permission of Captain Edye, li. N., our observing station was on Duntze Head, the point to which the longitudes are referred in the elaborate survey, by the officers of the English navy, of the waters around Vancouver Island. The following are the results obtained for latitude, each value depending on a single altitude : Duntze Head. O 1 It O ' " September 4, 1869, y = + 48 25 47 September 8, 1869, <p = + 48 25 25 37 34 40 39 39 45 33 46 58 56 31 48 52 50 37 48 58 50 65 54 63 43 35 52 9 49 62 59 49 58 67 56 48 55 <p= + 48 25 452".o <p = + 48 25 491".3 Our observations for time give the following corrections of the standard chronometer, Negus 1316, on local mean time ; the date of the observations being expressed in the time of this chro- nometer : h m s 1869, Sept, 4.3417, 8 11 39.50.28by 16 altitudes of the sun. 1869, Sept. 4.3417, 8 11 39.20.38 by 12 altitudes of a Bootis. Adopted, 8 11 39.4 0.24 A set of twelve altitudes of the sun observed with a Dollond sextant, owned by Mr. Very, the navigator of the United States Steamer Mohican, give for this correction 8 h ll m 40 S .60 8 .35 212 REPORT OF PROFESSOR HALL. The comparisons and rates of the chronometers give the following values of the longitude of Dnntze Head from Mare Island Navy Yard: Chronometer. Marti Island, September 4. 3417. Duutze i oad, September 4. 3417. Longitude. Ncdis 1316 Ti m s 8724 k m 8 8 11 39 4 ll III 8 + 4 37 00 8 Negus 1276 3 6 39 5 3 11 17 5 _|_ 4 38 o-^o 7 Negus 1097 8 8 12 1 8 12 50 5 -(- 4 38 41 4 Dent 2118 10 50 34 8 10 55 97 _j_ 4 34 9^1 8 50 57 8 8 55 35 4 -f- 4 37 61 8 Negus 772 7 45 21.2 7 50 3 4 -f- 4 42 21 7 Ne^us 1287 9 32 32.8 9 37 9 4 -f 4 36 60 6 Desilva 694 8 55 6. 3 8 59 44 7 _|_ 4 38 4^2 1 Negus 1317 10 44 4.8 10 48 45 2 + 4 40 4'i Negus 1298 8 13 32.8 8 18 9 2 + 4 36 40 7 Combining the several results according to their weights, the longitude of Duntze Head from Mare Island is + 4 m 37 B .l0 8 .40 The probable errors of the longitudes given by the single chronometers have been deduced by comparing the rates of the chronometers among themselves, and serve only for a combination of the various results. The real probable error of the final result is no doubt greater than that given above ; but to determine it would require an investigation of the temperature coefficients, and the stationary and traveling rates of each chronometer. Assuming the longitude of our observing station on Mare Island to be 8 h 9 m 1 8 .0 west of Greenwich, the longitude of Duutze Head is, by our observations, 8h 13 38 s .l The position of Duntze Head given in the English survey is Latitude = + 48 25' 49" Longitude = + 8 U 13 m 47 8 .1 An increase of the longitude of Mare Island will probably result from the telegraphic determi- nation of the longitude of San Francisco by the United States Coast Survey ; and this will bring the preceding results for longitude into better agreement. The sextant observations were made by Mr. Joseph A. Eogers and myself, both of us generally taking part in the observation, one using the sextant and the other observing the time. As our determinations of latitude depend on the Pistor & Martin's Patent Sextant No. 107, 1 have made a series of measurements of the distances between known stars in order to test the work of this sextant. The following table gives the results of these measurements : Objects. Distance. Errors. No. of measure- ments. a Arietis to /? Arietis o 3.9 // // + 9. 13.6 20 a Tanri to fi Tanri 16.8 + 2. 43. 1, 14 34 2 7. 34. 3 20 66 8 7.23.7 19 a Tauri to a UrsiE Minoris 72.8 93 3 + 1.02.7 10.03.0 12 15 115 2 1. 15.7 15 OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 213 The resulting errors are so small and of such a character that I shall not make any correction of the sextant observations. Prom the 115 measurements, the average probable error of a single measured distance is 15". 1. All the astronomical observations were recorded on loose sheets of paper, and soon after, gen- erally the next day, they were copied into blank-books. The observations are deposited at the Xaval Observatory and can be referred to at any time if need be. MAGNETIC OBSERVATIONS. I- The observations for magnetic declination at Plover Bay were made with a compass needle 6 inches in length. The compass circle is divided to 30'. A sharp, pointed rock off West Head, and very near the sea horizon, was selected as the point of reference in azimuth. The azimuth of this rock was determined by sextant observations, on August 4th and Oth. The azimuths deduced from the observations are <>1 >0 0'.3 and 01 58'.5, counting from the south towards the west, and the mean value 01 5!V.4 has been adopted. The declination was determined also by direct observations of the sun on August 3, 4, and 5. The observation of August 4 was made through clouds, but as it has the advantage of a different position of the sun, it has received the same weight as the others. The following are the results obtained. D;itc. Object observed. Declination. Observer. 1869. 7i. m. o / Aug. 3. 6 55 j>. in. Sun. 19 42. 2 East. H. 4. fl l!4 a.m. Sun. 19 54. 3 H. 5. 4 30 p. in. Pinnacle. 19 30.0 H. 5. 50 p. HI. Pinnacle. 19 34.6 H. 5. 6 7 p.m. Sun. 19 39.0 H. o / Mean value 19 40. East. The observations for dip and intensity were made with the Barrow dip circle No. 4, lent to us by Professor Peirce, Superintendent of the Coast Survey. The vertical circle of this instrument has a diameter of Di inches, and is divided to 10'. The instrument is furnished with two common needles for observing the dip, and with two Lloyd needles for observing the relative intensity. In observing, it was mounted on a tripod, and the observations were made in open air, without pro* tection for the instrument. The instrument was first leveled, then the plane of the vertical circle was made perpendicular to the magnetic meridian by using one of the needles, and finally brought into that meridian by means of the horizontal circle. The readings and reversals were then made in the usual manner. During an observation with a Lloyd needle, the thermometer, Fahrenheit, was read four times, and the thermometer was placed so as to give the temperature of the needle as nearly as the observer could judge. The Lloyd needle was used first without the weight, then with the weight in the inner hole, then with the weight in the outer hole, and lastly, without the weight. The mean of the first and last observations was taken as the dip of the unloaded needle. The weights were inserted in the A ends of the needles, a weight having been provided for each needle. The observations were recorded in convenient forms furnished by Professor Harkness. In the following table of results and o 1 denote the dip of the needle with the weight in the inner and outer holes: 214 REPORT OF PROFESSOR HALL. OBSERVATIONS OF MAGNETIC 1)11'. Date. Station. Needle 1. Net-die 2. Temp. Observer. 1869. h. m. o / / o May 15. 9 10 a. m. Washington. 71 15. 71 23.4 69.0 H. Dec. 1. 1 38 p.m. Washington. 71 6.1 71 34.6 57.0 H. 2. m. Washington. 71 6.5 71 52. 7 56.0 H. Aug. 4. 9 30 a. in. Plover Bay. 74 41.3 74 35.5 54.0 H. 4. 10 p. m. Plover Bay. 74 36.6 74 34.7 55.0 R. 5. 10 a.m. Plover Bay. 74 41.3 74 43. 4 49.0 H. Sept. 6. 11 a.m. Esquimalt Navy Yard. 70 46. 3 71 20. 72.0 H. 7. 12 p.m. Esquimalt Church. 70 59. 8 70 55. 6 67.6 R. 9. 11 7 a.m. Esquimalt Church. 71 17. 8 71 27.0 80.8 H. 23. 14 p.m. Yerba Buena. 60 32.5 63 6.8 92.9 R. 24. 9 55 a, m. Yerba Buena. 62 5.6 64 14. 7 81.5 H. OBSERVATIONS WITH THE LLOYD NEEDLES. Date. Time. Station. Needle. Dip. 9. e i . Temp. Obs'r. 1869. h. m. o / c / 1 o May 15 10 15a.m. Washington ... 1. 71 48.5 23 42. 4 50 23. 8 74.0 H. 10 45 a. m. Washington ... 2. 70 55.6 37 23.2 56 23. 76.0 H. Dec. 1 2 10p.m. Washington ... 1. 72 29. 2 20 19.8 42 51. 9 50.2 H. 2 50 p. m. Washington ... 2. 71 25.4 35 40. 8 55 9.2 47.2 H. 2 32 p. m. Washington ... 1. 72 26. 8 14 6.7 39 20. 5 55.0 H. 54 p. m. Washington ... 2. 71 25.6 34 59.5 54 58.5 49.6 H. June 23 10 45a.m. Yerba Buena ... 1. 63 5.8 35 35. 7 54 20. 2 70.1 H. 11 50a.m. Yerba Buena 2. 63 39. 47 7.8 58 39. 76.7 H. 24 11 23 a. m. Yerba Bnena - - - 1. 62 27.9 36 14.5 50 13.2 63.9 R. 7p.m. Yerba Buena . . . 2. 61 12.4 45 59. 56 59.0 66.2 R. Sept. 23 41 p.m. Yerba Buena . . . 1. 63 49. 1 39 33.5 49 49. 92.5 R. 16p.m. Yerba Buena . . . 2. 62 3.0 44 42. 5 56 40.5 92.9 R. 24 10 23 a. m. Yerba Buena ... 1. 63 44. 8 33 30.7 49 4.2 80.0 H. 10 45a.m. Yerba Buena ... 2. 62 15.0 44 3.8 56 51. 2 80.9 H. Aug. 3 6 p. m. Plover Bay .... 1. 74 54.3 37 45. 8 60 19.5 50.2 H. 6 30 p. m. Plover Bay .... 2. 75 16.2 51 1.0 64 48.5 48.4 H. 4 11 30a.m. Plover Bay .... 1. 76 16.4 37 21.5 57 34.0 59.5 R. 15p.m. Plover Bay .... 2. 74 30.2 52 27. 8 67 1.0 63.1 R. 5 11 a. m. Plover Bay .... 1. 75 35. 1 29 33.0 60 34. 8 51.8 H. 1 p. m. Plover Bay .... 2. 74 46.5 51 54.5 65 50.0 50.0 H. Sept. 4 1 23p.m. Esquimalt Navy Yard 1. 72 59. 3 28 42. 49 19.0 64.3 H. 2 4p.m. Esquimalt Navy Yard 2. 71 30.0 42 15.2 56 42. 8 67.0 H. 6 Om. Esquimalt Navy Yard 1. 72 10.2 30 56. 5 45 45. 8 76.0 H. 40p.m. Esquimalt Navy Yard 2. 71 45.4 41 55.0 57 23.8 74.5 H. Sept. 7 11 10a.m. Esquimalt Church . . 1. 73 1.6 29 50. 5 44 44.0 64.6 R. 11 40a.m. Esquimalt Church . 2. 71 25. 41 26.7 58 7.5 67.0 R. 9 11 30a.m. Esquimalt Church . 1. 73 9.3 27 55.2 50 11.0 75.5 H. Om. Esquimalt Church . 2. 71 28.1 41 31.2 58 11.5 70.2 H. OBSERVATIONS OF THE ECLIPSE OF AUGUST 7, 1869. 215 The temperature at Yerba Bueiia was observed in June with one of the ship's thermometers. This thermometer had a graduation on the tube, and also a graduated scale attached. The two graduations differed as much 15 in the higher temperatures. The graduation on the tube was used in the observations; but a few days after, and before any comparison with our own thermome- ters, this thermometer was broken. In September the station at Yerba Buena was intensely hot. The magnetic station at Washington is in Mr. Schott's garden on Capitol Hill; at Yerba Buena, the station is on the beach at high-water mark, and 150 feet north of the government pier on the eastern side of the island the same that was occupied by Professor Harkness in 1866; at Plover Bay, near our observatory on the sand pit ; at Esquimault navy yard, about 40 feet west of the entrance gate in the open yard north of the road ; and at Esquiiuault church. 50 feet west of the English church, near the signal staff erected by the United States Coast Survey. The geograph- ical positions of these places are as follows, the longitudes being reckoned from Greenwich: Place. Latitude. Longitude. Washington Yerba Buena o / 38 53. 1 north 37 48.8 " 64 22.4 " o / 76 59. 9 west 122 20. 7 " 173 19.5 " Egquimalt Navy Yard Esquimau Church . . . 48 25. 8 " 48 25. " 123 26. 5 " 123 26. " For the value of the magnetic dip to be used in computing the relative values of the magnetic force, I have taken for each station the means of the values observed with the common needles. The values of the dip given by these needles are as follows : Washington - 71 19.2 Washington 71 24. 7 Plover Bay, Siberia 74 38. 8 Esquimalt, Vancouver Island 71 7. 7 Yerba Buena . 62 29.9 (May.) (December.) By comparing the above values of the dip with the values given by the Lloyd needles, the cor- rections for these needles are, Needle 1, s = 65'.6 ; Needle 2, c = 4'.5 The observations at Washington give the only means of estimating the effect of a change of temperature on the values of the dip given by the Lloyd needles. . Hence we have Needle 1, A5= I'M At-, Needle 2, A3 = I'M At. The values of the coefficients have been found from a change of temperature of 25 ; but an examination of the observations will show that disturbance from other sources, probably a slight rusting of the needles, is so great that it is not worth while to apply any correction for temperature. If if be the total magnetic force at a station, S the corrected dip of the Lloyd needle, and the dip of the needle when loaded with a weight, and <p^ 3^ o l denoting similar quantities at another station, we shall have by Dr. Lloyd's method <f _cos . sin (<*i 0i) >i~cos 0j. sin (S e)' 216 REPORT OF PROFESSOR HALL. Our observations give the following values of S and 0; two values of <> being observed with each needle as the weight was inserted iu the hole nearest and farthest from the axis : Station. Needle. <i H ' Washington . . 1 O 1 71 2 6 o / 20 27 3 ' 36 21 6 Washington . 2 71 6 45 45 55 43 4 Yei'lja Buena. 1 62 9 3 36 13 6 45 28 3 Yerba Bueiia. . . 2 62 12 9 50 51 7 57 17 4 Plover Bay .... 1 74 29 7 34 53 4 51 47 8 Plover Bay 2 74 46 5 59 29 4 65 53 2 Ksquiiualt 1 71 44 5 29 21 41 47 1 Esquinialt 2 71 27 6 47 30 57 36 4 Assuming that the force at Washington is expressed by the number 13.35, (in English units,) the forces at the stations are found to be as follows : Yerba Buena, force = 11. 61 11.64 11. 71 11.78 Mean = 11. 68 Plover Bay, force = 12. 38 11. 90 11.96 12.23 Mean = 12. 12 Esquinialt, force = 12. 65 12.83 13.22 13.09 Mean = 12. 95 After our return to Washington an examination of the needles shows that they have rusted a little, a condition not surprising considering the long sea voyage. I am very much indebted to Mr. C. A. Schott, of the United States Coast Survey, for instruc- tion and advice in using the magnetic instruments. BAEOMETER AND THEEMOMETEE. The barometer used at Plover Bay is a mercurial ship barometer, made by Green, of New York. We had no opportunity of comparing it with a standard barometer. The thermometers are No. 38 and No. 39, by Negretti and Zambra, of London. They were exposed so as to give the temper- ature of the air in the shade. By comparison with the standard thermometer of the Naval Obser- vatory Professor Eastman found that these thermometers require the correction respectively of +0.2 and +0.3, and a comparison since our return shows that these corrections have not changed. No corrections have been applied to the observations following: OBSERVATIONS OF THE ECLIPSE OP AUGUST 7, 1860. 217 Date. Hour. Barometer. At. Ther. Ther. No. 38. Ther. No. 39. li. m. in. O o o 1869. Aug. 1 7 p. m. 29. 74 50.0 50.2 50.0 2 10 a. in. 29.78 48.0 47.3 47.1 2 8 15 p. m. 29.79 48.7 48.3 48.5 3 8 15 a. in. 29.90 52.2 54-.0 53.8 3 3 p. m. 29.90 54.5 53.2 53.0 3 6 45 p. in. 29.86 50.8 47.3 47.2 4 7 15 a.m. 29. 61 52.2 52.7 52.4 4 1 15 p. m. 29.58 57.2 55.4 55.3 4 3 45 p. in. 29. 58 56. 56.6 56.4 4 7 45 p. in. 29.61 51.6 51.6 51.4 5 8 (1 a.m. 29. 55 46. 6 46.0 45. H 5 12 in. 29. 62 51. 7 49.9 49.7 ' 5 6 30 p. m. 29. 72 55. 3 47.5 47.2 6 8 45 a.m. 29. 56 46. 5 45. 2 45.0 6 3 45 p. in. 29. 49 56. 5 55.2 55. 4 6 11 p. m. 29. 65 46. 3 44.4 44.4 7 7 a.m. 29. 83 7 11 15 a. m. 29. 90 49. 4 55.0 55.1 When about leaving Washington I received from Mr. W. H. Ball a Smithsonian blank for a comparative vocabulary of the natives at Plover Bay. This blank I filled up, and in doing this I was assisted by Mr. William E. White, who has been engaged for several years in trading on that coast. From Lieutenant Commander Louis Kernpff, United States Navy, I have a pretty full vocabulary of the Indians of our northwestern coast and of Vancouver Island. I am very much obliged to Professor Coffin, Superintendent of the Nautical Almanac, through whose kindness we were provided with several instruments, and at whose request Professor B. Otis Kendall procured from the University of Pennsylvania the telescope used by Mr. Rogers in observ- ing the eclipse. I am also under obligations to Mr. John Downes, of the Nautical Almanac, who computed the occultations of several stars visible at Plover Bay. Finally, 1 tender my sincere thanks to Mr. Joseph A. Eogers, of the United States Hydro- graphic Office, my companion in the expedition, who did everything possible to make our success complete. Very respectfully, your obedient servant, ASAPH HALL, Professor of Mathematics U. 8. Navy. Connnodore B. F. SANDS, U. S. N., Superintendent of the U. S. Naval Observatory, Washington, D. C. 28* X 4- o t- o x ^ W : -ce CD *-J cti i I PH "C5 a o ce 0) gg IV Q ri O 0< W & Plate HI. miANGVLATION CONNECTINGTHE TEMPORARY OBSERVATORIES AT DES MOINKS,IOWA, IN AUGUST 1869. Srale, Naval <s ,-' Observatory \^x West Signal North Base East Signal latohfield O \i s ervHtory O iOO 2OO tlOO -*OO .TOO ftOO 7OO Metres 2000 ajoo Feet . IVoCWm Harkness.U.S.N.del. J.Bien I. Hi Plate IV THE SPECTROSCOPE .l.Bien lith Plate V. Sun n in. IV V. Seal ( of Tin Is . ./' .7 Spectra observed. Pn.lMV Hnrklii-KS I' > \.,1,-1 KMorns clirinnohrti II ll N'oon -Mi. PLATKim. 6JL. r/er/ifm/ /rn I'llVW n/j.vtr\rffiijft.v>i-iffi the Photometer. f f'ntw ran ober\-atianjsiv't}> the Actinontelt f Avff. IO.O 0.0 lix'ttKiinv ti/' ('(ii'iiiin mill / J ittfutiririnr<'.v irntnrtlititfty ajlrr of CffT"ontt- etfj^ef Pt'otuliemn fe..v /rtst r/*W of 7'otafity. rnrt Plate X. 1)1. K. Ciii-lia. L'.S.A .ph'it". TOTAL ECLIPSE OF THE SUN, AUGUST 77? 1869. Appearance of Phenomena after comiiiciiceinem of Totality. Fac- simile of Photograph N 62. Plate XI . Dr.E. Curtis t'.S. A .photo. .I.Bien lith. TOTAL ECLIPSE OF THE SUN, AUGUST 7 1869. Appearance of Phenomena near the close of Totality Fac- simile of Photograph N 63. The Coiona of the Total Eclipse uf August 7.1869, as seenhythe aid of a four inch tele sc OL P RETURN MAIN CIRCULATION ALL BOOKS ARE SUBJECT TO RECALL RENEW BOOKS BY CALLING 642-3405 DUE AS STAMPED BELOW JUN 2 2 1994 FORM NO. DD6 UNIVERSITY OF CALIFORNIA, BERKELEY BERKELEY, CA 94720 U.C.BERKELEY LIBRARIES UNIVERSITY OF CALIFORNIA LIBRARY