Coast Survey of the United States. 233 
tendent. He not only arrives at the most correct determination 
of latitude compatible with the means allowed him, but is ren- 
dering valuable aid towards the thorough investigation of a very 
interesting question, a question intimately connected with his 
future discussions of the figure of the earth. 
In connection with this subject, it may be mentioned that it is 
the design of Dr. Bache to employ observations of transits over 
the prime vertical for the determination of latitudes, as soon as 
the requisite instruments can be supplied. During the preceding 
‘ winter the latitude of Cambridge observatory was determined in 
this manner, with such admirable coincidence in the results as to 
leave nothing to be desired. 'The observers were, Major Graham 
of the Topographical Engineers, Mr. Wm. C. Bond, the director 
of the observatory, and Mr. G. P. Bond, his son. The observa- 
tions were reduced by Prof. Peirce, and will appear in the Trrans- 
actions of the American Academy. They have also been com- 
municated by Prof. Peirce to the office of the coast survey. 
Astronomical azimuths require also frequent determinations in 
order to ensure accuracy, and to save the ungrateful labor of re- 
trospective calculation. With regard to this important element 
in geodesy it is theoretically true, that when one azimuth has 
been defined, others can be deduced from it by simple calculation 
in the progress from station to station. But repeated measures 
for verification are indispensable to avoid error, and to escape the 
trouble of reoccupying old stations. During the preceding season 
the azimuthal bearing was ascertained, independently, for six of 
the primary stations, four at the north and two at the south. 
Of the two heavenly bodies most commonly used in this ope- 
ration, Mr. Hassler preferred the sun, but Dr. Bache has employ- 
ed for the first time on the work, the elongations of Polaris, in 
both its eastern and western digressions. His objection to the 
sun is the exposure of the instrument, which cannot fail to be 
affected by the heat of this luminary. 
A distinguished astronomer, it may be remarked, directed the 
English surveyors never to use the sun for any geodetic deter- 
mination. ‘The prominent advantage in using Polaris, is the op- 
portunity it affords for a very careful and deliberate observation. 
At the time of elongation, when the change of altitude is most 
rapid, the movement in azimuth is nothing ; there is ample time 
therefore to repeat the measurement until satisfied with its ex- 
