236 EIGHTH ANNUAL REPORT OF 



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

 submitted. 



The planet Neptune. 



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 Pierce, 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 184S and 

 1S49, 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 1S53 and 1854, after which the whole will be trans- 

 ferred to the Nautical Almanac. 



Occultations. 



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, and hence this phenomenon becomes a ready means of deter- 

 mining the difference of longitude between two places. The employ- 

 ment of occultations for fixing geographical positions is easy, and leads 

 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 occur- 

 rence of occultations renders the use of them of great importance to the 

 travelling 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 ex- 

 ploring and surveying expeditions now carried on by our government 

 and our people, and to be continued for an indefinite time in the exten- 

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

 Southwest. 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 appro- 

 priation 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 en- 

 terprise 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 



