206 AN ACCOUNT OF THE 
observations, which the peculiar construction of that instrument, enabled 
the French astronomers to take with great facility in a comparatively short 
time. On account of its portability and extensive power, I think the 
repeating circle, improved as its construction now is, by Mr. TrovucuTon, 
would be an excellent instrument te employ in mountain surveys: though 
it is true that some extra calculation is requisite to reduce the oblique 
angles of objects not of the same apparent altitude. 
Our English circles give the horizontal angles directly, and no correc- 
tion is necessary, but when they are of great power, they are very heavy 
and difficult to carry in the rugged mountains, and require firmer suppor- 
ters than we can always conveniently make for them. ‘With regard to 
"TROUGHTON’S reflecting circle, itis certainly an admirable instrument, and 
above all others, well suited to the purpose for which it is intended, 1. e. 
the taking of lunar distances at sea or on shore, as well as for taking alti- 
tudes. It may be thought that we were not so successful m making use 
of its powers as we should have been, but it will be seen by the close 
accordance of the observations of latitude made with it at Sehdranpir, 
by Lieutenant Hererrr and myself, that if we could have been as 
well satisfied with the results taken in the mountains, we might have 
dispensed with measuring the base. At Sehdranptir we cculd observe 
at our ease, and the temperature was equable, but on the Chii* the 
case was widely different, and T am much inclined to think that the 
great ‘difference of temperature between the two places altered, by 
ihe effect of the ‘contraction of the metal of the circle, its identity, if 
i may be allowed so to term it. On the Chur the cold at nights was so 
