QB W361 Y. ffOF-M1ICHI i /7?J a/ -.- ^ - -. c STATEMENT OF WORK DONE AT THE HARVARD COLLEGE OBSERVATORY I DURING THE YEARS 1877-1882. BY EDWARD C. PICKERING, r DIRECTOR OF THE OBSERVATORY. 4 i 1p i 1; ~ flat 1 '40 -w CAMBRIDGE: JOHN WILSON AND SON. anibersitt jCress. 1882. STATEMENT OF WORK DONE AT THE HARVARD COLLEGE OBSERVATORY DURING THE YEARS 1877-1882. BY EDWARD C. PICKERING, DIRECTOR OF THE OBSERVATORY. CAMBRIDGE: JOHN WILSON AND SON. 1anib8sit p2ress. 1882. HARVARD COLLEGE OBSERVATORY. 1877-1882. 0 IN the autumn of 1878 an effort was made to secure for the Observatory an annual subscription of five thousand dollars for five years. It was claimed that, with this, the current work could be doubled, and that much progress might be made in reducing the large amount of past observations which had been accumulating for several years. It was also anticipated that the results attained would be sufficient to justify the continuance of this annual increase by means of an endowment. About seventy ladies and gentlemen of Boston and vicinity responded to this call, and by their generous aid have placed the Observatory in its present improved condition. As the subscription terminates this year, the last instalments being payable next March, the present seems to be a proper time to show how far the promised results have been attained. An attempt will also be made to show that the condition of the Observatory has been so greatly improved by this subscription that it would be most unfortunate that it should relapse to its former condition. A subscription of one hundred thousand dollars is now in progress, and if secured will permit a permanent condition of activity. It will be noticed that the increased amount of work is quite out of proportion to the increase of income. This is to be expected, since a large part of the expenses are the same in either case, and the increase is therefore 4 directly available for the attainment of scientific results. The formation of a corps of skilled assistants also requires time, and a delay in securing a continuation of our present income would seriously reduce our capacity for attaining results with the greatest economy both of time and money. As an increased expenditure was undertaken before the completion of the subscription, it is deemed best not to limit the present report to a period of exactly five years, but to include all the work undertaken since my first connection with the Observatory in February, 1877. The effect of the subscription may be summarized in a few words. Without it, only one instrument, the meridian circle, was kept actively at work, the large telescope being comparatively idle. The reductions even of this one instrument could not be kept up, but every year fell more and more behindhand. With the subscription, the large telescope, the meridian circle, and the meridian photometer, are in constant use. A large number of the old observations have been published, while the remainder have been reduced, and before long will be ready for publication. One volume of the recent observations with the large telescope has already been published, another volume of meridian photometer observations is now passing through the press. The unfinished volumes of Annals were completed so that, as is shown below, our work is now known through twelve quarto volumes, while in 1876 but four had been given to the public. Eight more volumes of Annals will be needed to complete the publication of the observations already made. The increased rate of work ensues simply because the corps of assistants has been more than doubled. Below will be given in order the various researches undertaken with the large equatorial, with the meridian circle, and with the meridian photometers. Then will be considered other researches, the distribution of standard time and the various publications that have been made. Fifteen assistants are at present attached to the Observatory. A large part of the work to be done consists of copying or computing of a very simple 5 character. By a proper division of labor, such work is done economically, the time of the more skilful assistants being reserved for the more difficult work. In this way researches can be carried out in a few years which are beyond the reach of the less favored observatories where the corps of assistants is small, or where such work can only be done if the astronomer is willing to devote the best years of his life to a single research. It should be observed that many of the investigations named below are of great extent, involving many thousand observations, and in many cases an amount of computation which would render it impracticable for a small observatory to prepare the work for publication without a delay of many years. LARGE EQUATORIAL. The large telescope has been devoted mainly to photometry,that is, to a measurement of the light of the stars. As but little work of this kind had been done with large telescopes, it was necessary to devise instruments for this purpose, have them constructed, and learn by experience the various errors to which each was subject. As over a dozen forms of photometers have been tried in this work, the labor involved in addition to that of observation has been very considerable. The principal investigations undertaken with the large telescope have been the following:Satellites. - Measurements of the light of the satellites of Mars were undertaken immediately after their discovery in 1877. These measures were repeated in the oppositions of 1879 and 1881. Similar measures were made of the satellites of Jupiter, Saturn, Uranus (outer satellites), and Neptune. A long series extending over one hundred and twenty-one evenings was made of Iapetus, the outer satellite of Saturn, to determine the law by which its light varies. Pclipses of Jupiter's Satellites. - The importance of observing these phenomena has long been recognized. Hitherto the time 6 of disappearance or reappearance has alone been noted. Errors are thus introduced dependent on the size of the telescope, the sensitiveness of the eye of the observer, the haziness of the air, and, worst of all, a systematic error arises from the effect of twilight when Jupiter is observed near the sun. All of these errors are eliminated by comparing the satellite photometrically with another near it. Instead of single determinations we thus obtain whole series, each of which gives as many independent values of the true time of disappearance as it contains separate observations. By the aid of one or two assistants from seven to twelve settings per minute may be secured. These observations were begun in June, 1878, and since then one hundred and eighty eclipses have been observed. It is proposed to continue these observations for at least twelve years, during an entire revolution of Jupiter around the sun. Double Stars. - The relative light of the components of over two hundred double stars was measured in 1879-80. Each star was observed in more than ten sets of four settings each. Faint Stars. - A hundred very faint companions to bright stars were selected in 1878 and observed photometrically. Several asteroids were similarly observed. A map of the stars in close proximity to the pole was constructed, and careful measures were made of the brightness of these stars, to make them available as standards for other observers. Planetary Nebulce. - A photometer was devised for measuring the brightness of the nebulae, and applied to all the planetary nebulae. The spectrum of each was also examined, and the diameters of most of them determined. New Planetary Nebulce. - The simple plan of placing a direct vision prism in front of the eye-piece of a telescope appeared to be an easy method of detecting minute planetary nebulae by their spectra. Some interesting objects of this class were found 7 which could not be distinguished from stars without the prism. Stars could thus be examined very rapidly, many thousand being viewed in a single evening. A systematic series of sweeps has been undertaken, zones 5~ by 10~ equally distributed over the sky being selected. From these the inference may be drawn that these nebulae are not to be found far from the Milky Way. A number of sweeps have accordingly been made in the Milky Way, and have led to the discovery of eleven of these objects. One was so bright that it had been observed as a star, without a suspicion of its real character. Two objects were also found having a very singular spectrum of bright lines, one being quite unlike that of any other known star. In the course of the exploration two new variable stars were discovered. Variable Stars.-Photometric observations of the variable stars have generally proved less satisfactory than those made by the eye alone. A new photometer, however, overcame the usual difficulties and gave light curves of several variables of the Algol class with great accuracy. About three thousand measures were made of each star, the observations generally extending over several hours. In one case nine hundred measures were made in a single night, extending without intermission from seven o'clock in the evening until the variable had attained its full brightness, at half past two in the morning. Moon. - The light of different portions of the moon's surface is ordinarily estimated according to an arbitrary scale. The Selenographical society of England were invited to select a series of points as standards, and the promise was made to measure their light photometrically. The Society accordingly selected about fifty such points, which were measured here, and the results transmitted to the Society (Selenographical Journal, V. 57). Bond Zones. -A large part of the work of the Observatory during the years 1852 to 1860 consisted in the determination of 8 the positions of about fifteen thousand stars between the equator and one degree north. Plans are now in progress for the revision of those between + 50' and + f 1', comprising about one fifth of the entire list. These stars will be observed with a modification of Professor Pritchard's wedge photometer, by which their light may be determined very rapidly during their transit across the field. This determination of the light of a large number of faint stars will afford a means of extending the present photometric scale of magnitudes. Convenient standards for comparison will thus be furnished for other faint stars. Incidentally the positions of the stars will be measured and a comparison made with their places, as observed more than twenty years ago. It is hoped that some interesting cases of variability or of large proper motion will thus be detected. In no other part of the heavens have we such precise determinations of so many very faint stars, and the observations of Professor Bond may thus acquire a value beyond that of simple catalogue positions. Satellites of Mars. - The amount of photometric work accomplished has prevented the accumulation of many micrometric measurements. In special cases, however, an attempt has been made to supply observations not likely to be obtained elsewhere. In 1877, beside the photometric measures of the satellites of Mars, a series of measures of their positions was also made. The number of these observations was second only to that obtained with the great telescope at Washington. This was partly due to the use of a shade of red glass, which in the following opposition was generally adopted at other observatories. In 1879,thirteenl hundred and forty-eight measurements of the satellites were made, Deimos being last seen at this Observatory as it gradually receded from the earth. This is remarkable as our telescope has entered into competition with the largest telescopes in the world, some of which admitted two or three times as much light. 9 Comets. -By securing the services of Mr. Chandler as an assistant, and by the co-operation of Mr. Ritchie of the Science Observer, a scheme has been developed which has made a great advance in the early announcement of comets. When a comet is discovered, notification is usually sent to this Observatory by telegraph. If the discovery was made in this country, a telegram is at once sent to the Dun Echt Observatory, and thence distributed throughout Europe. The following evening, if clear, an observation of the comet is taken, and the resulting position telegraphed to Europe. These early positions have in some cases proved of great value, and have been used again and again in each subsequent orbit. Great care has been taken to avoid all delay in sending them, with the result that occasionally these precise positions have become known abroad before the discovery itself had been announced by the usual method. As soon as these observations are obtained, the computation of the orbit is begun, and the work continued at all hours of the day or night until the results have been translated into the Science Observer cipher and cabled. About four days after the comet is discovered, its elements and ephemeris are generally printed and distributed in this country and in Europe. By an arrangement with the Signal Service and with other observatories, when cloudy weather is expected here observations are sometimes obtained elsewhere to avoid delay. Such arrangements have been made with the daily papers and with the Associated Press, that any important observation made here before midnight would probably be printed in the papers of the following morning in the principal cities of the country. By the same system of co-operation a plan for sweeping for comets has been developed, in accordance with which a number of observers have undertaken to examine a certain portion of the heavens once or twice every month, and satisfy themselves that no comet within the reach of their telescope is to be found there. The results published in the Science Observer show that the entire heavens is now so thoroughly swept that a comet is not likely to be long visible without detection. 10 Miscellaneous Observations. - Among those may be named the determination of the focal length of the large telescope, the pitch of the screw of the micrometer, observations of asteroids, and a careful series of preliminary observations for determining stellar parallax. MERIDIAN CIRCLE. The observations carried on with this instrument during the period here discussed may be classified as follows: - Zone Observations. - This series of observations was undertaken in 1870 as a part of a general scheme for the observation of all stars of the' ninth magnitude or brighter, situated north of the equator. The work to be accomplished was shared by a number of observatories in Europe and America. The stars observed here are those situated in the zone from 50~ to 55~ north of the equator, with an extension of 10' into the adjacent zones on both sides, in order to provide means of connecting the results obtained here and elsewhere. These observations were carried on by Professor Rogers from the autumn of 1870 to January, 1879, when they were completed except so far as the reductions may show the need of revision to remove discordances. The work has included two complete observations of each of about eight thousand three hundred stars, with numerous additional observations of fundamental stars from which the instrumental corrections are derived. Coast Survey List. -A list of two hundred and fifty-eight stars requiring observation for geodetical purposes was drawn up by the United States Coast Survey, and an arrangement was made with this Observatory to furnish such observations. The plan involved six observations of each star. The work was begun in January, 1878, and completed in one year. Standard Stars. - The principal work of the Meridian Circle after February 15, 1879, consisted in the determination of the 11 absolute co-ordinates of rather more than one hundred of the brighter stars. This work involves daily observations of the Sun and observations of the stars at all times of the night and day. It has occupied three years, but two years more will be required to complete it according to the original plan. Miscellaneous Observations of Stars and Planets. - Observations have been frequently made at the request of other astronomers for special purposes. Mr. Gill, now Director of the Royal Observatory at the Cape of Good Hope, desired the places of a number of stars used in his observations for the parallax of Mars and of some asteroids. These places were accordingly determined here, and subsequent observations were made to investigate the difference apparently existing between bright and faint stars as determined at different places and by different observers. Observations of Mars and of neighboring comparison stars were also made in pursuance of a proposition made by Professor Eastman. Observations of certain stars were made at the request of Professors Davidson and Hall, of Captain Tupman, and of M. Bossert. The comparison stars used in determining the places of several asteroids were likewise observed, and two observations were made of Comet 1881, III. Instrumental Constants. - One of the graduated circles of the instrument has been minutely examined with the aid of special contrivances for detecting errors of graduation. A long collimator has been put up on the grounds of the Observatory, by means of which small variations in the direction of the line of sight have been studied. Many experiments have been tried with levels of different kinds for the purpose of discovering errors, and observations of stars have been made in order to show whether the telescope revolves in a vertical plane. Its flexure, likewise, has been carefully discussed, with the unexpected result that the value of this quantity for each year is found to be about 0."6 greater in January than in July. 12 MERIDIAN PHOTOMETERS. In 1878 an instrument was devised by which any star when crossing the meridian could be compared with the Pole-star. The working of this instrument proved highly satisfactory, and many of the errors were avoided to which other photometers are subject. The images to be compared are precisely alike, and are viewed with the same magnifying power, aperture of telescope, and emergent pencil, on the same background, and in general under the same conditions. The stars are observed very rapidly, over a hundred having been measured (with four settings on each) by a single observer in one evening. A catalogue of all the stars visible to the unaided eye in the latitude of Cambridge was prepared, and each of these was observed on at least three evenings. Nearly half were observed twice as often, or on six evenings each, and some important stars still more frequently. The entire work was completed in less than three years, and furnishes a measure of the light of about four thousand and three hundred stars. Nearly one hundred thousand settings are involved in this work. The results are now being put in type, and will include a discussion of the constancy of the light of the Pole-star, the variation in the atmospheric absorption at various altitudes, and a comparison of the nomenclature of various authorities. An important part of the work will be a comparison of the scales of magnitudes employed by various authorities from the Almagest to the present time. A comparison will finally be made of the light of each star according to the separate authorities after applying a proper correction for this difference of scale. To afford a better means of comparison with the results of the eye observations, each of the stars of the northern heavens has been compared by three observers with a series of standard stars. Two catalogues are thus obtained, one giving the light of the stars as seen with the naked eye, the other, the true light as indicated by the photometer. Interesting results are anticipated from a comparison, as showing the effect of the proximity of bright stars, of the background of the Milky Way, etc. 13 The success of the first meridian photometer led to the construction of a similar instrument of much larger size and of improved form. The apertures of the telescopes were four inches instead of an inch and a half, and various changes were made in the details. With this instrument the light of any star brighter than the ninth or tenth magnitude may be determined. It will be used for a still larger piece of work than that above described. In the revision of the stars of the northern heavens, referred to in the description of the work of the meridian circle, the zones of the various observatories overlapped by a small amount. Over eight thousand stars are contained in these overlapping portions, and therefore are each observed at two observatories. The light of all these stars is to be determined with the new meridian photometer, and the estimates of light of the various observers in the entire work of revision may thus be reduced to a single standard. Incidentally, the scale of various catalogues will also be determined. Besides this work, the standard stars of the Uranometria Argentina, the comparison stars for variables, and other objects of interest will be measured. MISCELLANEOUS OBSERVATIONS. Meteorology. - A portion of the meteorological observations of the Observatory are still kept up, but less importance is attached to them than formerly, on account of the vast amount of material now being collected by the United States Signal Service. Attention is rather directed to the more unusual and less observed phenomena. In this connection may be named a careful study by Mr. Searle of certain zodiacal phenomena, especially that designated by Brorsen as " Gegenschein." longitude Determinations. - The attention now paid at Washington to the determination of longitude renders the prosecution of this work at Cambridge less necessary than formerly. In any important work of the kind it is, however, still desirable to determine the longitude from this Observatory, since for many years it was the standard meridian in this country to which all 14 others were necessarily referred. It also served as the basis from which the longitude of America from Europe has been found. The most important longitude campaign recently carried on here has been the determination of the difference in longitude of Detroit and Cambridge, which connects the system of the Lake Survey with that determined from this Observatory. The difference in longitude of New Haven and Cambridge has also been determined. Variable Stars. - An important piece of bibliographical work has been undertaken in collecting all the observations hitherto made of the variable stars. This has led to the formation of a catalogue of over a thousand stars whose light has been supposed by various authorities to be variable. Of the known variables of long period the observed times of maxima and minima and their corresponding brightness have been in part already collected. Finally, it is proposed to select the more important observations, more especially those in which the variable is compared with one or more stars of constant brightness, and reduce them to a uniform scale. The comparison stars will probably be measured with the meridian photometer. Preparations are now being made to enlist the aid of amateur astronomers and others in a scheme for determining the constancy or variability of all the suspected variables referred to above. Also for determining the light of all the variables of long period at intervals of a month or less throughout their entire variation from maximum to minimum. If many persons can be induced to take part in this work, a very important addition to our knowledge of the variable stars will be attained. No instrument is required but a telescope or even an opera-glass. Besides the more experienced observers it is hoped that many persons interested in astronomy but unaccustomed to such work will undertake it, as with care the needed skill is readily acquired. The education of a class of observers from those who have hitherto failed to add to our knowledge of the science would be in itself a most important work. Doubtless, should the plan 15 prove successful, many professional astronomers would be willing to co-operate in the matter, and thus greatly add to the value of the research. Standards of Lengths. - An important comparison of the various standards of length has been conducted by Professor Rogers, in addition to his Observatory work. In connection with this work he visited London and Paris in 1880, and obtained some important comparisons with European standards. He has also devoted much attention to the construction of standard scales with equal subdivisions, and his work has proved essential in the observations of the Transits of Mercury and Venus. Atmospheric Refraction. - For several years past investigrations involving many thousand observations have been in pry gress, under the direction of the Rumford Committee. Measures have been made at temperatures varying from +920 to -12~ to determine the effect of changes in this disturbing element. TIME SERVICE. For many years an important service rendered by the Observatory to the public has consisted in furnishing an accurate standard of time. This department has been improved and extended in various ways. Two new clock rooms have been constructed, and various devices introduced for increasing the regularity and accuracy of the signals furnished. With the co-operation of the Signal Service and of the Equitable Life Assurance Company, a time ball has been erected in Boston, and is dropped every day at noon. A full description of this ball will be found in the Professional Papers of the Signal Service, No. 5. PUBLICATIONS. The following tabular statement of volumes wholly or partly in print, belonging to the Annals of the Observatory, exhibits in 16 successive columns the general subject of each volume or part, the instrument chiefly used in the observations described in it, the epoch of the observations or of the events discussed, and the date of publication. An asterisk in the first column denotes that the distribution of the corresponding work took place during the period covered by this report. The publication and distribution of Vol. XIII., Part II., and of Vol. XIV., will probably occur in 1883. Date of Vol. Part Subject. Instrument. Epoch. Publication. I I History and Description. 1840-55 1856 I II Zone Catalogue, 5,500 Stars East Equatorial.. 1852-53 1855 II i The Planet Saturn... 1847-57 1857 II II Zone Catalogue, 4,484 Stars t 1854-55 1867 III Great Comet, 1858... 1858 1862 IV I Catalogue of Standard Stars 1855 1863 IV* ii Right Asc., 505 Stars.. East Transit Circle 1862-65 1878 V Nebula of Orion.... East Equatorial.. 1847-65 1867 VI* Zone Catalogue, 6,100 Stars " 1859-60 1872 VII* Solar Spots....... West Equatorial. 1847-49 1871 VIII* i History and Description.1856-76 1876 VIII* i Astronomical Engravings. East Equatorial.. 1872-74 1876 IX* Photometric Researches. Zllner Photometer 11872-75 1878 X* Places of 1200 Stars... Meridian Circle..1868-72 1877 XI* I Photometric Observations. East Equatorial..1877-79 1879 XI* II cc it 1877-79 1879 XII* Places of 628 Stars... Meridian Circle.. 1871-75 1880 XIII* I Micrometric Measurements East Equatorial.. 1866-81 1882 XIII II Meteorology.. 1840-79 XIV Meridian Photometry.. Mer. Photometer. I1879-82 Material for about eight volumes of Annals, in addition to those above named, has been collected, and these volumes might be completed and published in the absence of any further observations, except with the large meridian photometer. The subjects of the volumes are described briefly below. A large part of the observations has been reduced, and several of the volumes can soon be prepared for printing. 17 Observations of fundamental stars made before 1879, and various series of similar determinations carried on between 1870 and the present time. Observations of the stars between 50~ and 55~ north declination. Catalogue of stars resulting from observations just mentioned. Observations, in 1879 and later, of the standard stars mentioned above in describing the work of the Meridian Circle. Miscellaneous photometric work, chiefly with the large equatorial, 1879 and later. Photometric observations of the eclipses of Jupiter's satellites. Photometric observations with the large meridian photometer. Variable stars. Besides the researches which have appeared in the Annals above mentioned, a large number of articles relating to astronomy and kindred subjects have been published, during the period here considered, by the astronomers connected with the Observatory. A list of these is given below. By William A. Rogers. New Elements of Iphigenia (117) from the Opposition Observations of 1870, 1872, 1873, 1877. (Astronomische Nachrichten, XCI. 107.) On Standard Measures of Length. (Am. Quarterly Microscopical Journal, Jan. 1879.) On two Forms of Comparators for Measures of Length. (Id. April, 1879.) On the Limits of Accuracy in Measurements with the Telescope and the Microscope. (Proc. Am. Acad. of Arts and Sciences, XIV. 168.) On the First Results from a new Diffraction Ruling Engine. (Am. Journal of Science and Arts, Jan. 1880; 3d Ser. XIX. 54.) On the Present State of the Question of Standards of Length. Presented April 14, 1880. (Proc. Am. ecad. of Arts and Sciences, XV. 273.) On Tolles's Interior Illuminator for Opaque Objects. (Journal of Royal Microscopical Society, III. 754.) The Coefficient of Safety in Navigation. (Proc. U. S. Naval Institute, VII. No. 3. Science, April, 1881; 11.'171.) 18 On a Convenient Method of Expressing Micrometrically the Relation Between English and Metric Units of Length on the Same Scale. (Proc. Am. Assoc for Advancement of Science, Aug. 1881; XXX. 116.) On a Method of Reducing Different Catalogues of Stars to a Homogeneous System. (Id. XXXI. 11.) On the Performance of a New Form of Level Invented by Mr. John Clark of the U. S. Coast Survey. (Id. XXXI. 14.) Plane v. Cylindrical Surfaces. (Mechanics, No. 31, p. 90.) A Study of the Problem of Fine Rulings with Respect to the Limits of Naked Eye Visibility and Microscopic Resolution. (Am. Monthly Microscopical Journal, Sept. 1882, p. 165.) A Comparison of the Harvard College Observatory Catalogue of Stars for 1875.0 with the Fundamental Systems of Auwers, Safford, Boss, and Newcomb. (Memoirs of the Am. Acad. of Arts and Sciences, X. 389-429.) On the Conditions of Success in the Construction of Standards of Length and in their Subdivision into Equal Parts. Read before the American Society of Microscopists at the meeting held at Elmira, N. Y., Aug. 1882. (Mechanics, Oct. 27, 1882 and later.) By Arthur Searle. On Certain Zodiacal Phenomena. (Astronomische Nachrichten, XCIX. 91, 369; CII. 263. Science Observer, July, 1882; IV. 4.) By Leonard Waldo. Standard Public Time. (Observatory Circular, 1877.) Engineer's Instruments and their Adjustments. Boston, pp. 40, 1. 8~. On the Longitude of Waltham, Mass., Nov. 1877. (Proc. Am. Acad. of Arts and Sciences, XIII. 175.) A Lecture on Telling the Time. (Bulletin of Essex Institute, Feb. 1878; X. 40.) Note on the Measurement of Short Lengths. Feb. 1878. (Proc. Am. Acad. of Arts and Sciences, XIII. 352.) Observations of the Satellites of Mars, and of Double Stars. (Astronomische Nachrzchten, XCII. 87.) 19 Meridian Observations of Mercury at its Transit. May 5-6, 1878. (Id. XCII. 361.) Observations of the Satellites of Saturn. (Id. XCIV. 339.) Report of the Observations of the Total Solar Eclipse, July 29, 1878, made at Fort Worth, Texas. Cambridge, 1879. 4~. Articles "Transit," " Sextant," "Telescope," "Ruling Machine," "Time Signals," " Mural Circle," " Zenith Telescope." (Johnson's New Universal Cyclopaedia, New York, 1877-78.) Description of a New Position Micrometer. (Am. Journ. of Science and Arts, July, 1880; 3d Ser. XX. 49.) On the Adaptation of the Opera Glass to Extremely Myopic Eyes. (N. Y. 0phthalmological Journal, 1880.) By Winslow Upton. Observations of Minor Planets. [W. Upton and W. A. Rogers, observers.] (Astronomische Nachrichten, XCIII. 171.) Determination of the Orbit of (185) Eunike. (Id. XCIV. 51.) By 0. C. Wendell. Observations of Comet c 1879 (Swift). (Astronomische Nachrichlen, XCVI. 21.) Observations of Comets 1881 V. and 1881 VIII. (Id. CI. 231.) Observations of Comets 1880 IV. and 1881 II. (Id. CI. 299.) Observations of Comets 1881 III. IV. VI. (Id. CIII. 145.) Comet (b) 1881. (Science Observer, Aug. 1881; III. 81.) By J. Rayner Edmands. Geodetic Formulae. (Appalachia, July, 1880; II. 135.) Report of Councillor of Topography. (Id. July, 1880; II. 161.) Geodetic Formulae. [Second Paper.] (Id. Dec. 1881; II. 351.) The Mountains between Saco and Swift Rivers. [With map.] (Id. June, 1882; III. 57.) * e0 0ee By S. C. Chandler, Jr. Elements of Comet b 1881. (Astronomische Nachrichten, C. 121.) Elements and Ephemeris of Comet e 1881. (Id C. 319.) Observations and Elements of Barnard's Comet, 1881 VI. (Id. CI. 57.) On the Periodicity of Comet (Denning) 1881 V. (Id. CI. 93.) On the Variability of DM.l + 23~ 1599. (Id. CII. 139.) On Sawyer's Variable, DM. +1~ 3408. (Id. CII. 371.) On the Telegraphic Transmission of Astronomical Data. (Science Observer, Aug. 1881; III. 65.) Letter to the Astronomische Gesellschaft on the Science Observer Code, (Vierteljahrsschrift der Astronomischen Gesellschaft, 1881, XVI. 344.) Elliptic Elements of Comet (f) 1881-Denning. (Science Observer, Dec. 1881; III. 91.) On a New Variable Star in the Constellation Cetus. (Id. March, 1882; III. 105.) On Sawyer's Variable, DM. +1~ 3408. (Id. July, 1882; IV. 11.) On the Period of R Hydrae. (Will appear shortly.) By Edward C. Pickering. The following list contains the titles of similar works of my own during the same period, including those of an official character, describing the work of the Observatory, as well as those containing the results of special researches. The Micrometer Level. (Apwpalachia, June, 1877; I. 138.) Address of the Vice-President, Section A. (Proc. Am. Assoc. for Advancement of Science, Aug. 1877; XXVI. 63.) Annual Report of the Director of Harvard College Observatory, presented to the Visiting Committee November 26, 1877. Cambridge, 1877. 8~. Report on the Progress of the Zone Observations. (Fierteljahrsschrift der Astronomischen Gesellschaft, 1877, XII. 290.) Annual Report of the Director of Harvard College Observatory, presented to the Visiting Committee November 14, 1878. Cambridge, 1879. 8~. 21 The Cosine Galvanometer. (Nature, Jan. 1879; XIX. 217.) Stellar Magnitudes. (Astronomische Nachrichten, XCV. 29. Nature, May, 1879; XX. 14. Astronomical Register, XVII. 175.) Thirty-fourth Annual Report of the Director of the Astronomical Observatory of Harvard College. Presented to the Visiting Committee December 5, 1879. Cambridge, 1880. 8~. Report on the Progress of the Zone Observations. (Vierteljahrsschrift der Astronomischen Gesellschaft, 1879, XIV. 387.) Observations of the Satellites of Mars. [E. C. Pickering, O. C. Wendell, A. Searle, and F. Waldo, observers.] (Astronomische Nachrichten, XCVII. 115, 145.) Light of Webb's Planetary Nebula. (Nature, Feb. 1880; XXI. 346.) Dimensions of the Fixed Stars, with especial reference to Binaries and Variables of the Algol Type. (Proc. 4Am. Acad. of Arts and Sciences, June, 1880; XVI. 1.) Two New Planetary Nebulae. (Nature, Aug. 1880; XXII. 327.) Novel Celestial Object. (Id. Sept. 1880; XXII. 483.) New Planetary Nebulae. (Am. Journal of Science, Oct. 1880; CXX. 303. The Observatory, March, 1881; IV. 81.) Thirty-fifth Annual Report of the Director of the Astronomical Observatory of Harvard College, presented to the Visiting Committee December 6, 1880. Cambridge, 1881. 8~. Variable Stars of Short Period. (Proc. Am. Acad. of Arts and Sciences, Feb. 1881; XVI. 257. The Observatory, Aug. —Oct. 1881; IV. 225, 264, 284.) Observations of Comet III. 1869. (Astronomische Nachrichten, XCIX. 95.) Observation of the Solar Eclipse of Dec. 30, 1880. (Id. XCIX. 107.) The Companion of Sirius. (Id. XCIX. 219.) Photometric Magnitude of Jupiter's Satellite III. (The Observatory, April, 1881; IV. 113.) Large Telescopes. (Proc. Am. Acad. of Arts and Sciences, April, 1881; XVI. 364. Nature, Aug. 1881; XXIV. 389.) Photometric Measurements of the Variable Stars / Persei and DM. 81~ 25, made at the Harvard College Observatory. [E. C. Pickering, Arthur Searle, and 0. C. Wendell, observers.] (Proc. Am. Acad. of Arts and Sciences, April, 1881; XVI. 370.) 22 Objects remarkable for their Colors or Spectra. (Astronomische Nachrichten, XCIX. 375.) New Variable Star in Puppis. (Id. C. 13.) Comet 1881, III. (Science, July, 1881; II. 329.) Report of the Committee on Standards of Stellar Magnitude. (Proc. Am. Assoc. for Advancement of Science, Aug. 1881; XXX. 1.) Thirty-sixth Annual Report of the Director of the Astronomical Observatory of Harvard College, presented to the Visiting Committee, November 10, 1881. Cambridge, 1882. 8~. Report on the Progress of the Zone Observations. Vierteljahrsschrift der Astronomischen Gesellschaft, 1881, XVI. 317.) Reply to inquiries regarding Time Balls. (Professional Papers of the Signal Service, No. 5, p. 24.) Stars with peculiar spectra, discovered at the Astronomical Observatory of Harvard College. (Astronomische Nachrichten, CI. 73.) Order of Brightness of Stars. (English Mechanic and World of Science, Nov. 1881; XXXIV. 278.) Remarkable Star Spectrum; New Planetary Nebula. (Science, Dec. 1881; II. 581. Copernicus, Dec. 1881; I. 242.) The Pleiades. (Astronomical Register, Feb. 1882; XX. 40.) Variable Stars. (English Mechanic and World of Science, Feb. 1882; XXXIV. 542.) Photometric Observations of Planets and of Jupiter's Satellite III, made at the Harvard College Observatory. (Astronomische Nachrichten, CII. 151.) Photometric Observations of the Satellites of Mars, 1881-82. [E. C. Pickering and 0. C. Wendell, observers.] (Id. CII. 193.) The Meridian Photometer. (Monthly Notices of the R. Astr. Society, June 1882; XLII. 365.) Photometric Comparisons of Lunar Objects. (Selenographical Journal, JulyAug. 1882; V. 53, 57.) Erratum in Observations of Comet Wells, 1882. (Astronomische Nachrichten, CII. 223.) Photometric Measurements of Sawyer's Variable (DM. +1~ 3408), and its Comparison Stars. (Id. CIII. 61.) New Planetary Nebulae. (Id. CIII. 95, 165.) 23 Small Planetary Nebulae, discovered at the Harvard College Observatory. (The Observatory, Oct. 1882; V. 294. The Sidereal Messenger, Oct. 1882; I. 139.) A Plan for Securing Observations of the Variable Stars. Cambridge, 1882. 8~. Whether the next five years shall prove as fruitful of results as the last, or whether the Observatory shall relapse to the much less active condition in which it was obliged to remain before the subscription of 1878, will depend on the result of the effort now being made to increase its endowment by one hundred thousand dollars. EDWARD C. PICKERING. Photomount Pamphlet Binder Gaylord Bros., Inc. Makers Syracuse, N. Y. PAT JAN 21, 1908 UNIVERbSIlY UF MICHIGAN 3 9015 00905 8069l IIIII I 3 9015 00905 8069 -1.; ~ r-, ~;: f -i. r -Fr~ -i:?: itJ -r '3;;.YRPPBBa`~;asnCarnaBiC1J .: -1 I r;i rcse ;lss4c,rg:h3 ~i:r,4iiPZZ9 cu;e:IA`hYS(P:?bTLf ii