1853.] 



DAVIS'S REPORT ON THE NAUTICAL ALMANAC. 



been discussed anew, according to tlie raetliod of least squares, 

 and the work is left in such a form tbat the observations of all 

 observatories, particularly those of Washington and Greenwich, 

 on account of the complete form in which they ai'e given to the 

 world, can be used from year to year, for the continued improve- 

 ment of the elements of the planets. The perfection of the places 

 of these planets is the more important and valuable that they are 

 used very constantly in lunar distances by the navigator, and their 

 erroi-s are highly magnified at the time they are best seen and 

 most useful, by the greater relative change in their distances 

 from the earth than in those of the other planets emploj'ed in 

 this way. 



In preparing the ephemeris of Jupiter and that of Saturn, as 

 well as in those of tlie jireceding planets, all the en-ors and alter- 

 ations pointed out by Professor Airy in the introduction to the 

 Greenwich Planetary Reductions, have been correetoi and adojited 

 and the tables of Bouvard and Lindenau have been entirely re- 

 modelled and reconstructed for the convenience of computation. 

 But it is well known to astronomers that the theor}- of Jupiter 

 and Saturn demands a thorough revision ; and their combination 

 presents a case of peculiar dilBcult}', which has been ably treated 

 by Professor Hauseu. To prepare Hansen's theory for use in 

 practical computation, is a work of time. It will be entered upon 

 immediately, and will probably be completed in the course of 

 two years. 



In the case of Uranus, there are no tables which can be relied 

 upon. Professor Pierce's theory, combined with the researches of 

 LeVerrier, will, for the first time, form the basis of the new 

 ephemeris of Uranus. 



With regard to the new planet Neptune, the world has already 

 accepted with grateful acknowledgments the labours which 

 American astronomers have conferred upon it with illustrious 

 success. The computation of the tables of the perturbations of 

 Neptune, by Professor Pierce, and the computation of the elliptic 

 elements of Neptune, by Mr. Sears C. Walker, have resulted in 

 the preparation of an ephemeris, by the last named gentleman, 

 ■which admits of no sensible correction. 



The ephemeris of the fixed stars has also been improved by 

 the introduction of the latest and most approved constants of pre- 

 cision, nutation, and aberration. 



The general list of occultations has been very much extended, 

 in order to make it especially useful to geographers in general, 

 the boundary and other surveyors of the government in the inte- 

 rior, to the coast survey of the United States on both oceans, and 

 the explorei's of unknown parts of the continent. 



Other changes regarded as improvements might be recited. 

 The astronomical part of the ephemeris has been adapted to the 

 meridian of Washington ; siderial dates have been introduced ; 

 what is believed to be a more correct obliquity of the ecliptic 

 has been adopted; and more convenient forms and a better 

 typographical execution are kept in view. A woik comprising 

 such a multiplicity of details may admit of many similar 

 amendments. 



To the above it should be added, that an entirely new reduc- 

 tion has been made of the early Greenwich observations of Mars, 

 by Bradley, Bliss, and Maskelyne, preparatory to a new theoiy 

 and to new tables of this planet. 



A new method, with new tables, of clearing lunar distances 

 will be given in the first number of the almanac, in which im- 

 provements are presented leading to the correction of eri'oi-s of 

 ten, fifteen, or twenty minutes in the longitude, common to the 

 methods at present in use; which errors may, in rare cases, 

 amount to a whole degree. 



There are two other signal advantages to be derive! from the 



publication of the Nautical Almanac, the mention of which should 

 not be omitted : they concern the navigator, surveyor, astronomer 

 and geogi-apher. 



. One of these is a more complete, full, and accurate table of 

 latitudes and longitudes, particularly of American latitudes and 

 longitudes, than is now anywhere to be found, 



These positions also embrace in their number the most con- 

 spicuous towns and trigonometrical stations, with their magnetic 

 and asti'onomical beanngs, along both sea coasts, and as tar in 

 the interior as the operalions of the coast survey extend. When, 

 therefore, the American surveyor or astronomer of a boundary 

 commis.sion opens the almanac for the requisite astronomical data 

 of his observations, he may find also such terrestrial data as will 

 answer for the proper basis of his field work, and at the same 

 time as the standard of accuracy to his own indejjendent compu- 

 tations. To meet his wants, some additional constants will be 

 occtisionally inseited, — as height of station above the sea, mean 

 barometric pressure, variation of the needle, <fec. And as a 

 separate list of the latitudes and longitudes of tlie principal 

 observatories of this country ana in every quai-ter of the globe is 

 a customary part of the almanac, so the stationary astionomcr 

 will, in turn, find his purposes served. An assistant is employed 

 in verifying the positions in the world generally, given in the 

 best European hsts; and a suitable selection will be made 

 from the determinations of the offices of hydrography, topo- 

 graph}', and the coast survey, to enrich the American table 

 with the best and most numerous list of American geographical 

 positions extant. 



Similar tables are published in the French almanac; but no 

 such tables, with the exception of the observatories, are given in 

 the British. This, therefore, is regarded as another improvement 

 in the American almanac upon the latter. 



The other signal advantage spoken of, relates to the subject of 

 the tides. The conduct of a general system of tidal observations, 

 their reduction, and their scientific discussion, by which is evolved 

 the rules for the prediction of the tides, are all the property of 

 the hydrographical and astronomical departments of the coast 

 survey. But it is the province of the Nautical Almanac to present 

 the results of these various labours in a manner suited to answer 

 the practical demands of navigation and engineering. 



It will not perhaps be irrelevant to cite a single case under the 

 general problem of the tides. In order to be able to give rules 

 practically useful to the pilot, engineer and seaman, for aiiphing 

 to the ordinary tides, corrections depending on the moon's vary- 

 ing distance and declination, it is necessary to know to what 

 meridian passage, or southing of the moon the tide isjdue; or, 

 what the distance is from the land of the general tide wa\'e that 

 causes the local tide which the observer is actually registering; 

 or, in fine, what is the age of the tide when it arrives at any 

 particular part of our coast. This knowledge is the residt of the 

 careful study of a large number of observations made at various 

 points. The age of the tide at London dift'ers from that at Key 

 West ; and that of Key West again from that of New York, or 

 Hampton Roads. 



Our exclusive dependence upon European authority for that 

 knowledge of our coasts which no Eiiropean authority can, from 

 the nature of the case, supply, has been a disadvantage and a 

 reproach. Both the disadvantage and the reproach the Amei'i- 

 can Nautical Almanac will help to remove by making use, as it 

 has been authDrized to do, of the materials in the records of the 

 coast survey, for furnishing a tide table founded on the actual 

 observations of tides in our own northern and southern harbours, 

 and their subsequent reduction and discussion in the office of 

 that institution. 



One consequence of the announcement of the preparation of 



