Lien Bia Soi a 
igs 
Calis WM 
ee les ee 
. he favorite 
Review of the Results of the U.S. Coast Survey. 258 
to the open polar sea, to the discovery of which so much atten- 
tion has been recently directed, and which appears to be in fact 
only a forgotten reality. 
ave adverted to the observations of latitude, azimuth 
and longitude as requisite to determine the position on the earth’s 
surface of the stations, the relative situation of which as to dis- 
tance and direction is ascertained by triangulation. They serve 
thus incidentally to determine the figure of that portion of the 
over which the work extends. While in other countries 
extensive operations have been executed for the special purpose 
of measuring arcs of meridians and parallels, the Coast Survey 
furnishes those important additions to one of the highest depart- 
the results already obtained. They exhibit a general conformity 
to be not only such as would result from want of uniformity in 
the geological structure in the immediate vicinity of stations, 
but to extend like undulations over considerable regions 
h e 
Vertical transit, the zenith telescope (or equal altitude instru- 
lat 
— Sector of the British Ordnance Survey, the only other of 
Tivalled by those of the zenith telescope, the application of which 
to Webereasione of latitude by equal elias altitudes of stars 
46 the north and south of the zenith is of American origin and 
has en greatly perfected in the Coast Survey. Combining 
Portability and facility of use, with great aceuracy, it has become 
av instrument, and no observer, who has ever used it, 
8 willing to return to others , 
. “n order to bring out the various elements of error, observa- 
instruments, with the same instrument by different observers, 
Y the same observer with two different instruments of the 
