Chauvenet’s Spherical and Practical Astronomy. 383 
is quite right i in calling the instrument ners invention of Capt. 
Talcott.” We have supposed it was rather an improved form 
of the old zenith telescope, the maeblticien taking the place of 
a graduated arc, although the readings of the graduated are in 
the old instrument were ae as well as in the new 
instrument with the micrometer. methods of observation, 
owever, and the processes of selva belong to our Coast 
Survey, and are in this work very satisfactorily explained. The 
method given for determining the —— by extra-meridian 
observations with this instrument is original. 
hapter IX treats of the Equatorial Daleecase, adopting Bes- 
sel’s method of introducing the flexure of the telescope and o 
the declination axis, and giving the most general formulas, even 
for the case where the pole of the instrument is quite remote 
from the celestial pole. The mode of determining the actual 
equatorial sa nent ag is investigat a a subject we do not . 
remember to have seen elsewhere discuss ae The conilel 
theory of the Heliometer, according to Bessel, is next given in 
a concise and simple manner, yet with the same extreme aceu- 
racy that we find in all the other parts - the learned author's 
work, The Ring Micrometer is next discussed. The correction 
of all kinds of micrometric observations, ae refraction, table for 
‘the 
nutation, and aberration. The formula for the latter purpose is 
e same as that of Bessel, but the method of pa ata is 
oo 
elegantly and concisely di eloped, in gm clearest foeta i in which 
it has ever been our fo - —— = rg oes bi 3 cae 
m aca oo faserents which have n not unfrequen 
“ Gade and confuse the subject are ae 3 
