H2 



ASTRONOMY. 



Greenwich Ephemeris, and those obtained hy corresponding observations at Greenwich_, was 

 pretty generally + 12'. This confirms the importance of a thorough revision of the lunar 

 tables. The uniformity observable in these results shows, I hope, the probability of detecting 



the error, and eliminating or reducing it. 



I have deposited in the Department of the Interior two volumes containing, in tabulated 

 form, all the individual observations and computations upon which the results obtained on the 

 boundary for longitude are founded. I give a leaf from these volumes, to show the manner in 

 which the observations were made and computed. It has been suggested to me to present them 

 for publication ; but as each would make a volume nearly the size of the Greenwich Observa- 

 tions, I have contented myself, in this publication, with presenting in tabulated form the sepa- 

 rate results, and in two cases — at the initial point on the Pacific, and at the mouth of the Eio 

 Bravo— I have extended the table so as to show in detail the manner in which all the observa- 

 tions and computations have been tabulated. It has been found convenient, also, to incorporate 

 with these tables the computations by which the azimuth lines forming portions of the boundary 



were determined. 



III. Latitudes. 



I 



The latitudes of all the primary astronomical stations, except four, were determined either by 

 myself or by Assistant J. H. Clarlc, with the zenith telescope. Two of the four excepted were 

 determined by Lieutenant Whipple, the other two by Lieutenant Michler. I have placed in the 

 Department of the Interior four volumes containing the individual observations and the com- 

 putations for the latitude of the primary stations. In regard to the publication of these 

 volumes, the same remarks that were made above in reference to the longitudes apply here, 

 give a leaf from them also, to show the mode of tabulating and computing the observations: 



The tables attached hereto present a recapitulation of all the results for the latitudes of the 

 primary stations, including the station determined by Lieutenant Michler, by circum-meridian 

 altitudes of northern and southern stars observed with a sextant, and those determined by 

 Lieutenant Whipple^ by observing the transit of stars over the prime vertical. 



The method habitually used on the boundary for obtaining latitude — that by the measurement 

 of the difference of zenith distance of stars near the zenith, and nearly equidistant, north and 

 south — is now so generally used and approved as to make no particular notice of it necessary. 

 It was first adopted by Captain Talcott, in 1835, on the survey of the Ohio boundary. It was 

 resumed by myself on the northeastern boundary ; and some of my results coming under the 

 eye of Professor Bache, he concluded to try it on the Coast Survey, and called on me for any 

 suffcrestion I mi^rht have to make in reference to the form. I made the suggestions which 



^QV^^^.V^^ * *^-0 



resulted in the form in which the instrument is now made by Troughton & Simms, of London, 

 and is that which I used on the present boundary survey. 



Attached to the table combining the results of the observations at each station is a table 

 showing the correction applied to the places of stars^ derived either from actual observations of 

 stars at the Washington Observatory, and politely furnished for the use of the boundary sur- 

 vey, or from the Twelve-year Catalogue of the G-reenwich Observatory. 



A comparison of the results obtained by the zenith telescope, with the errors developed in the 

 declination of stars of the British Association catalogue, will show the rapid march field 



operations have made, in point of accuracy, upon the observations at the fixed observatories. 



