A. D. Bache on Determining Latitudes by Talcott’s Method. 343 
Arr, XXXVIII.—On a Supposed Personal Equation in the Use of 
the Zenith Telescope for Determining Latitudes by Talcoit's Method ; 
by A. D. Bacueg, Superintendent U.S. Coast Survey. 
(Communicated by authority of the Treasury Department.) 
THE use of the zenith telescope to determine latitudes for the 
Coast Survey by Talcott’s method has been explained in a paper 
read before the Association at the Cincinnati meeting in 1851. 
The difference of zenith distance of two stars passing the meri- 
dian nearly at the same time, one north and the other south of 
the zenith, and at nearly the same distance from the zenith, is 
measured by a micrometer. The sum of the same distance is 
star of the pair becomes known, and from its declination the 
latitude of the place. 
Observations at Mount Sebattis Station in Maine, in 1853, seem- 
ed to show that this method was not free from personal equation, 
Settling the question. . : 
At the tslesrialt station, Columbia, S. C., in 1854, assistants 
B. A. Gould, Jr., and G. W. Dean, observed with zenith tel 
No. 2 and No. 5. The latitude found by Mr. Dean with both 
instruments was almost identically the same, being with No. 2 
83° 59’ 58-14, and with No. 5 33° 59’ 58’-10, with probable 
errors from twenty-one pairs of stars, with the two instruments 
respectively of + 0-14 and + 0” 
ments and from the same stars, 
58-30 + 0-18, and 58-13 + 0-18. _ The spay was continued 
at ed Mountain station, Maine, in 1854, by assistant G. W. 
- Dean andsub-assistant Stephen Harris, under my direction, using 
instruments rae re) f stars. 
