IMAGE EVALUATION TEST TARGET (MT-3) V. / {/ / O te (/. ° '"% r/j 1.0 I.I m 111^ ijj^ 116 V. m 2.0 1.8 1.25 1.4 1.6 "^ 6" ► "/a J >^^ .^^ %' c. Otlu'i> move claliorate were sometimes made. In soTne all the ((nartcrs of tlie circli' were graduattil, lint this was probably to give ornament and liiiish to tiie in^trnmcnt. Soinctinu's a table was nttaehed to the diopter for determining the deellnation ol'the sun, lait as the table .-oon be- tainc incorrect, this attachment was of little importance. 14 zon. The transom was then moved until the end of it came into exact range with tlie middle of the sun, or to one edj^c allowing for the distance to the centre. The degree on the staff, cut by the edge of the transom at that moment, was the altitude of the sun. Our illustration is from an old drawing issued in London in 1G22. rr ip'iiiiii 8o 'I'liriii rm i iimi 'IMIIIIII If the observations by either of these two instruments were made when the sun was at the equinoctial, the altitude in der -ees thus taken, subtracted from 90°, would give the latitude. But if the sun, in its apparent course through the ecliptic, were either north or south of the equinoctial, then the next step was to ascertain the sun's declination. This was taken from a table calculated for every day in the year. As this required a bulky document, it was usually con- densed so as to occujjy but two pages by employing a Zodiacal Ephemeris, of which we give a drawing on the next page, taken from an old Treatise on Cosmography, dated London, 1594. It consisted, as may be sec umerous concentric circles, on the outer rim of which are display eu ihe signs of the zodiac, each covering thirty degrees, duly graduated and numbered. On the inner rim, in exact correspondence, av. represented the months of the year, divid- ed into spaces representing days, likewise graduated and numbered. By this instrument it was easy to find in what sign and degree the 1') Bun was on every clay tlirougliout the year. This Avas ascertained by hoklini^ f> slender silken thread at the centre of the instrument, and extending it through tiie point indicating the day of the month, on the inner rim, for which the declination of the sun was desired, Zotrttical ISpfjcmci'ts. carrying it to the outer rim of the circk', where it would rest upon the deijree of the siijn of tiic zodiac whicii the sun had reached on that day. Opposite to the degree thus found, in a table calcuhited for the purpose, occupying but a jmgle sheet, was set down the declini- tion of the sun for the day sought, in degrees, minutes and seconds. K) liii Ilaviiifv thus found the declination, if the sun was north of the equinoctial, it was to he suhtracted from the t^un's aUitude, or, if the sun was soutii of the eciuinoetial, it was to he added to the sun's altitude, and the remainder or sum, as the case might be, was sub- tracted from 1)0°, which <>ave the latitude soutjfht. Such were the instruments employed and such the method of tak- ing the latitude two hundred and fifty years ago, and indeed down to 1731, when the invention of liadley's quadrant introduced a new method, and gradually superseded the old instruments.' The reader has undoubtedly observed, not only that the probabilities of eri'or were numerous, but, that with the facilities which then existed, it was impossil)le for the navigator or ex[)lorer to determine the lati- tude with any degree of exactness. The following sources of error are especially notable. Both the Astrolabe and the Cross-staff were graduated only to de- grees. The disk of the former instrument was usuallv from five to seven inches in diameter. Long experience proved that a larger disk could not be successfully used by the explorer and navigator, on account of the jostling motion given to it by the wind or the movement of the ship at sea. Owing to the small size of the in- strument, the space occupied by each degree would, therefore, be considerably less than one tenth of an inch, and to graduate it to minutes it would be necessary to divide the minute space of less than one tenth of an inch into sixty divisions, which would be practically impossible. While therefore the operator in taking the altitude of '> Tlio pi-inci]ile involved in tlic reflecting quiidnint, commonly known ns liadley's Quad- rant, wiis diseovered by Sir Isaac Newton, ami, after liis doatli, which oceiirrcd in 1727, a description of it was found in iiis h.ind-writintc auionfj his jiapers. Iladley exhiliited liid invention at a ineelinit of tlic lloyal Society in 17:U. About the .same time Thomas God- frey, of Phiiadclpiiia, invented a similar instrument. The Royal Society decided that both Hadley and Godfiey were independent inventors. The invention of tliis instrument marks an era in obtaining trustworthy results in astronomical observations. After its introduction it was possible for nuiriucrs to take their hititutlc with nearly absolute exactness. 17 the sun could get the degrees with some certainty, what he put down as the fraction of a degree, or minutes, was an absolute and sheer guess. To determine to which of the sixty parts the diopter or in- dex pointed, when the wliolc space was less than a tenth of sin incii, was a process too delicate to be undertaken with any liope of success. In the old journals the minutes arc usually written in fractions of a degree, as one-fourth, one-third, one-half, two-thirds or three- fourths, but sometimes translated into minutes, and given as fifteen, twenty, thirty, forty or forty-five minutes, but Very rarely in any nmnber of minutes not represented by these general fractions. It is highly probable, indeed nearly certain, that the early navigators and explorers did not suppose that their statements of latitude would be interpreted with any degree of exactness as to minutes. They were at best but guesses, as they and doubtless all others at that period knew, with no ground or pretension whatever of certainty. But another not unimportant source of error is found in the old method of taking the siui's declination. The zodiacal ephemcris, or diagram then in use, of whicii we have given a drawing in the pre- ceding pages, was not graduated to minutes, and consequently there was an inaccuracy as to the exact point of the sun in the zodiac at the time of taking the latitude. But a still greater error arose from the tables used in connection with this instrument. These tables were not calculated annually, as is customary at the present time,* but were only renewed once in about thirty years. Owing to the precession of the equinoxes, which changes the equinoctial points at the r.ate of about 50" eacii year, these tables were constantly becom- ^ These tables are now found in the Astronomical Ephcmcrides, or Nautical Almanacs. They arc issued annually, under the authority of government, by Germany, Spain, Portu- gal, France, Great Britain and the United States. The French began the publication under the title of the Connaisance des Temps in 1679, and have continued it to tlie present time. The British Nautical Almanac was begun in 1767. The American Ephemcris has been pub- lished regularly since 1855. 3 18 ing inaccurate, and when used several years after the date of their calcuhition, as they often were, they furnislied an important source of error in ohtaining tiie declination of the sun. No account was taken or correction made, at the early period of which wc are treating, for the Dip of the Horizon, for Refraction or for Parallax, sources of error of minor importance compared with the larger ones to which we have referred," hut nevertheletJS of considerable gravity in working results, and carefully corrected by all navigators and surveyors of the present day. The method of taking the early latitudes which we have described, and the instruments employed, were in universal use. No better method or better instruments were known in any part of the world. The latitudes recorded by the explorers of that day in whatever quarter of the globe, if collated and tested, would be found subject to the same inexactness. It is undoubtedlv true that in cities, where structures could be erected for the accommodation and use of larger instruments, somewhat gi'cater exactness might be secured."" But these were exceedingly rare, and of course never practicable for the use of the roving navigator or the itinerant explorer. The result of these investigations leads us to three important con- elusions, wli.ch we may state as follows : I. The early latitudes are generally trustworthy to within a single degree. II. The minutes or fractions of degrees, as set down by writers anterior to the middle of the eighteenth century, are never to be re- lied upon, and are never correct except by accident. 9 These and some other minor sources of error were known to exist at an earlj* period, but their relations were so complicated and subtle that a correct knowledge of their quanti- tative value in astronomical calculations has onl j' been approximately determined at a com- paratively modern date. '0 Edward Wright, in 1594, took the latitude of London by observations of the " Polo Star," with a brass quadrant of six feet radius. It was found to be 51° 32', which is very nciivly correct. As no allowance was at that time made for refraction, the accuracy of the result must have been in part accidental. 1!) III. The annotfitioiiJ of tho learned coninicntators upon the lat- itudes recorded in the journals of our early navigators and explorers, in all cases in which they atten»j)t to identify places, within the limit of one degree, hy the latitude alone, cannot properly he cited as authority. It is to he remarked that some of the more recent writers, by col- lating with government surveys, have become aware of the discrep- ancy, at least in the cases which they have examined, but none of those, whose works have come under our own obfiervation, seem to have been clearly aware of the extent of the errors or of their true causes. If the latitudes of the early navigators had been determined with as nuich accuracy as is attained by the observations of the present day, some interesting historical questions might be definitely settled, and some not very decisive controversies might have been avoided. In such an event the Pye Bay of De Laet would probably not have been made identical with waters about ]Marblehcad." If the lati- tude of the little French colony on ]\Iount Desert, swept off by Sir Samuel Argal in 1G13, were surely at 44" 20', controversy would be cut short as to its exact location.'" If Weymouth's icaternirf place were clearly fixed in latitude 43" 20', several literary skirmishes would not have occurred,'^ and if AViiitson Bay were really in latitude 41° 25', we sliould no longer doubt whether ^lartin I'ring passed the summer of 1G03 in Plymouth Harbor in Cape Cod Bayj or in the little haven of Edgartown on the eastern borders of the isl- and of Martha's Vineyard." But more than this, if the triumphs of " Cf. Collections Xcw York Historical Society, ii. s. vol. i. p. 292. " Cf. Pierre Biard, Relations des JiJsuitcs, Quebec cd., vol. i, p. 45. " Cf. Collections Maine Historical Socicti/, vol. v. pp. 309, 344 ; vol. vi. pp. 293, 309, Me- morial of Poj}ham Celebration, p. 301. " Cf. New England IJistorical and Genealogical Register, vol. xxxii. p. 76. American Biography, hy Jeremy Belknap, D.D., vol. ii. p. 128. 20 science had been earlier, if the okl hititudcs had been taken with exactness, \vc siiouUl have been able I > trace the course, on sea and on shore, of the intrepid and immortal ex[)lorer8, who first penetrat- ed our northern waters, Davis, Frobisher, Barents, Hudson, Ilorc, Gilbert, Koberval, Cartier, and the rest, with the entiiusiastic satis- faction which certainty alwsiys imparts to historical investigations. It would have been far more gratifying, wc confess, if this inves- tigation had led us to the conclusion, that the old latitudes were al- ways correct. The haziness and doubt, however, which have so long brooded over the subject, have, wc think, been cleared away. And it will doubtless be admitted, that the certainty that the old latitudes were always wrong' is next in importance to the certainty that they were always right. ii:l ken with n sea and l)enetraf- n, Ilorc, 5tic eatis- itions. us invcs- wcro nl- B so long 7. And latitudes Iiat they