*244 EIGHTH ANNUAL REPORT OF 



Statement of all the facts connected with it, to his report, herewith 

 submitted. \ 



The planet NcjUnne. 



It has been mentioned in the last annual reports that Mr. S. C. 

 Walker, of the U. S. Coast Survey, prepared, at the expense of the 

 Smithsonian Institution, a memoir containing an exposition of the ele- 

 ments of the true orbit of the planet Neptune, and that from this orbit 

 and the mathematical investigation of Professor Peirce, of Cambridge, 

 an ephemeris of Neptune had been deduced, which has been accepted 

 by all the astronomers of the world, as the only certain guide to the 

 position of the planet. This ephemeris was prepared for 1848 and 

 1849, at the expense of the Institution; but since the last-mentioned 

 date it has been calculated at the expense of the appropriation for the 

 Nautical Almanac, while the cost of printing and distribution has been 

 defrayed by the Institution. The same arrangement will continue for 

 the ephemeris of 185o and 1854, after which the whole will be trans- 

 ferred to the Nautical Almanac. 



Occndtatio?is. 



The moon, in her passage eastward around the earth, continually 

 passes between us and the fixed stars or planets which lie in her path, 

 and obscures them from our view. The instant of the disappearance 

 of a star behind the moon, or the occultation of a star, as the phenome- 

 non is called, can be noted by observers widely separated from each 

 other, cUid hence this phenomenon becomes a ready means of determin- 

 ing tlie difl'erence of longitude between two places. The employment 

 of occultations for fixing geographical positions is easy, and le^ids to 

 accuracy in the results. The telescope may be of moderate size, and 

 requires no accurate adjustment; the position assigned it may be such 

 as to suit the convenience of the observer. The frequent occurrence 

 of occultations renders the use of them of great importance to the trav- 

 elhng observer ; and the publication of lists of these, and of tables for 

 their reduction, is essential to the improvement of geography. They 

 are of particular value in this country on account of the frequent explor- 

 ing and surve^dng expeditions now carried on by our government and 

 our people, ajad to be continued for an indefinite time in the extensive 

 territory of the West, and the newly acquired possessions of the South- 

 west. Tables of occultations for 1849 and 1850 were prepared and 

 published at the expense of this Institution ; but for subsequent years 

 the expense of their preparation has been defrayed by the appropriation 

 for the Nautical Almanac, under the direction of Lieutenant Davis, 

 while the composition and press-work are still at the expense of the 

 Institution. As soon as the Nautical Almanac is fully commenced, the 

 publication of" these tables will be entirely relinquished to this enterprise 

 of the government. 



Up to 1850 the tables published were of occultations visible in the 

 United States. Since, however, the preparation of the tables has been 

 in charge -of the director of the Nautical Almanac, the list has been so 



