Chauvenet’s Spherical and Practical Astronomy. 379 
ellipsoid of revolution, but it may be expected that, by elimin- 
ating as far as possible the anomalous Sevinieas in question, 
with the aid of the elements determined by Bessel, a very close 
os parang to the true figure will be obtained, 
Chapter IV, on the Reduction of Observations to the Centre 
of the Earth, another preliminary chapter, is almost exhaustive 
= the subjects of Parallax, Refraction, “he of the Horizon, | 
large a space in the work before us. Mr. Chauvenet adopts 
Bessel’s Tables, as thus far agreeing best with observation, and 
therefore limits himself to an explanation of the agate Ss by 
which that table is constructed. We notice that the autho 
0g ote trom theoretical considerations a formula for the zi of 
e horizon, including the effect of refraction, which ie 
tharkeably with the results of actual observation. The effect 
of refraction i pe the figure of the discs of the sun and moon 
is also pine p ated 
hapter V, on F jinding the Time by Astronomical Observa- 
tions, brings us fairly into the subject of practical astronomy, 
to which the preceding chapters are but introductory. This, 
together with Chapter VI, on Finding the Leahy an Chapter 
VU, on Finding the Long tude by astronomical obser is 
appears to embrace every pret nh known method of a 
value, with several new and simple methods, and is seuseiianine 
by numerous practical precepts which are designed to inculcate 
“sg rate habits of observation and precision in computation. 
f the many approximative methods of “ working a lunar dis- 
tance,” which have heretofore been given, Prof. Chauvenet gives 
but one, and that is his own. Any one who will take the trou- 
method rests, and b Tie hich his auxiliary tables are formed, will 
others. It isin the first place, accurate toa de. tart unapproached 
by any previous method except Bessel’s; in t 
ae of even the most ec ibeaee een! na ame 5 Sree 
the method was given to the world in the first volume of our 
American Ephemeris in 1855, we do not remember poring 
