THE NEW-YORK EXHIBITION ILLUSTRATED.
THE AMERICAN EPI-IEMERIS AND NAUTICAL ALMANAC.
STRONOMY, the complete scienceas we love to call it, and as it mayjustly be called in comparison withother branches of human know-ledge, is not wanting in her repre-sentations in the Crystal Palace. Itwould be strange if it were other-wise. For, from the most remoteages of the eastern world, dimlylighted as they are by the faintglimmerings of traditions, or. t euncertain interpretation of hiero-glyphic emblems, to the period ofyesterday, no science has been sothoroughly and so constantly inter-woven with the thoughts, the pas-sions,' and the business of men, asthe science of astronomy.
In that noble court of thebuilding which contains the pro-ductions of the Coast Survey, and
the instruments by which they areeffected, are to be found telescopesIn the French gallery are exhibitedsextants, quadrants, and circles; inone court is to be seen an orrery, anin another an astronomical globea series of astronomical maps.The special subject, however,
of our present notice is the . Amer
ican Ephemeris and Nautical Al-' manac,” and a set of new ‘Tablesof the Moon,” which may be seenin one of Mr. Putnam's cases. Ihecasual observer will regard these oo’s othe beauty of the typography on y, atheir publication forms a most important era~ P " " " in the progress of astronomical sc > e “°^“
this country, we feel bound to invite the attention of our readeis for aments to this interesting topic. We will premise what we ave oa succinct explanation of the nature and objects of the wor en 1 6 . oj f
American Ephemeris and Nautical Almanac,” which we extract iomits Superintendent, Oapt. Ohas. H. Davis, U. S. N. , ,
This work, published annually, each number of which consis s ofive and six hundred pages, embraces all the elements necessary or ( eat any time the absolute and relative places of the sun, moon, an sev
pal planets, of many of the largest and most useful of the xe s ai ’ .. ^
with several different series of phenomena for the determination oas occultations of fixed stars and planets by the moon, distances o , 16fixed stars and planets, combined transits of the moon an cer ame clipses and configurations of Jupiter’s satellites, &c. _ rules
To these are added the places of the minor planets and their e em >and tables for practical use in nautical astronomy and land o seija 1 ’
roles and methods whenever invented, tables of tides and geograp ica ’
and a chapter explaining the plan of the work and the mode o .
various parts in practice, in which is included some elemental y scie
These details are the result of numerous, laborious, and comphcatedjalc^Wons. Strict and uniform accuracy is an indispensable requisite. ag _
°f the mariner, errors expose life and property to danger; an in afronomer on the land, they cause a waste of time and labor, an no „
irretrievable loss of valuable opportunities. None of the precau ion , ’
that experience has pointed out for the attainment of correctness, ana gainst mistake, are neglected. ... „i, n _
The Nautical Almanac is stamped by this circumstance W1 f of itsuse-jacter. Unfailing precision and exactness as the J^nows that neitherfulness and respectability. But every person of exp conducted
s Uch extensive computations, nor the printing of so many figures, can be °°“
With entire freedom from er^r; and to remedy this defect, inherent m such pro-ductions, the errors detected are printed, and the corrections app ie ,sequent volumes, probably before the former come into genera use.
The calculations of the Nautical Almanac in reference o , ’
Principal planets, &c., are in the case of each one of them asekdge of their motions and the laws by which they are controlled, derived
the general theories of celestial mechanics, and from observations which, whilethey test the truth of the general theory, lead to the discovery of new factsand data, to the detection of other laws, and to the inference of new generaliza-tions.
The observations thus employed comprise all the calculations of good autho-rity, which from age to age have accumulated in the rich treasury of astronomicalscience ; ending with the latest publications of existing observatories, and goingback to the beginning of authentic history. In order suitably to convey ourknowledge of the laws governing the motions of the heavenly bodies and regu-lating their more or less rapid change of place, and to put this in a form adaptedto the wants and uses of the computer, numerical tables have been prepared ofthe sun and the planets separately, which constitute the abbreviated expressionsof these laws.
The numerical tables greatly facilitate the labor of computations; they arethe computer’s tools of trade. '
To construct these tables; to make, compile, and arrange these observations;to discuss them; to discover and investigate the theories and laws; and to inventthat kind of logic, the higher mathematics, by which alone such investigationscan be profitably pursued and their results succinctly defined,—have been the oc-cupations in every enlightened age of the most illustrious genius and the mostexalted talents. And a correct and well-conducted astronomical ephemeris, whichcomes up to the latest standard of modern improvement and discovery, is to bo re-garded as the full exponent of all this human thought and labor.
But from this very compendious exposition of the scientific character of the“ Nautical Almanac and Astronomical Ephemeris,” and of the intellectual basison which it rests, it may be well to turn to an inquiry into its practical utility,—•into the manner in which it has benefited mankind; for knowledge is always in-strumental in promoting the best interests of humanity.
The primary motive for computing and publishing the Nautical Almanac wasito promulgate the lunar method for determining the longitude at sea, and to fur-nish the requisite elements and precepts for the computation of this problem.This was as early as the year 1767. Its appearance created a new era in navigation,to which it is now acknowledged to have rendered more essential service thanany thing else ever undertaken. But the old lunar method of Maskelyne was verydefective, owing to the existing state of astronomical science and instruments. Asthe instruments of the seaman and the astronomer, however, were improved, and as-tronomy itself advanced, corresponding changes were made in the Almanac, whichsince its first foundation has always kept up with the progress of knowledgeand art; if not pari passu , at least without lagging behind for any great lengthof time.
It was discovered, soon after its publication was begun, that the work was des-tined to obtain general circulation as an astronomical ephemeris for the use ofobservatories, and that it would be impracticable, even if desirable, which it wasnot, to separate pursuits of practical science so closely allied to each other, andso effectually promoted by the same means. In the progress of time, therefore,as the pages of the Almanac were multiplied and their contents varied to meetthe wants and convenience of nautical astronomy, so the usefulness and suitable-ness of the work for the daily duties of observatories was increased, until it hasbecome no less indispensable to the fixed observor on the land than to the floatingobserver on the sea. And this could not be otherwise. The improvement ofnavigation is intimately connected with, and dependent on, the improvement inpractical astronomy. The security of the mariner, the advancement of thegeographer, and the refinements of the astronomical observer, are harmoniouslyunited and benefited by similar provisions.
To these considerations the “Nautical Almanac and Astronomical Ephemeris”is indebted for its present character and condition.
On the one hand, it is the text-book of the navigator. It informs him of hisplace on the ocean, where there are no other guides than the sun and stars. It ishis intellectual rudder and compass; without it no shipmaster leaves the shoresof the United States. When he loses sight of the last light-house or headland,he turns to that for his further direction.
On the other hand, it is the rode rnecum of the astronomer, whether station-ary or travelling. He learns from it in the fixed observatory how his instrumentsmust be set that he may see any particular body, and what is the precise momentfor observation; and in the movable observatory he turns to its pages to ascertainhow, on any given day, he can best determine his latitude and longitude, the as-tronomical bearings of his stations, and the rate and error of his chronometer.Thus, as the tables of the Almanac owe their origin to the labors of the Observa-tories, so they repay the obligation by affording the most ready and complete fa-cilities by which those labors are, at the present time, safely and expeditiously con-ducted.
Such are the general character and objects of a Nautical Almanac; but theAmerican Nautical Almanac, besides sustaining this character and fulfilling theseobjects, will, it is expected, remedy some defects, and accomplish some specialends, which no similar work prepared in Europe is qualified to take into account.
And what these ends are may be gathered from a consideration of the isolated