Chauvenet’s Spherical and Practical Astronomy. 381 
all the matter upon these subjects which belongs to r treatise 
on matpherion. riche, where the physical (ior of preces- 
n and nutation would be out of place. ; XII is 
equally Sts upon the methods of fico ne " Obliquity 
of the ecliptic and ane aeons Right Ascensions and Declina- 
tions of stars by observ 
The first volume ee with Chapter XIII, on the ici 
mination of Astronomical Constants by observation. This i 
brief but clear reswmé of the methods of determining anh con- 
stants of the refraction co the solar parallax, the mean 
semidiameters of the planets, the constants of precession, nuta- 
tion, and aberration, the parallax of a fixed star, and the motion 
of the sun. in ‘Space, 
Volume II is devoted to the Theory and Use of se tipo 
Instruments. Chapter I relates to the Telescope considered a 
from any form of mounting, and gives the methods of Lb et 
ing the magnifying power, ‘and a number of practical preva: 
necessary to the observer. 
Chapter II, on the Measurement of Angles, or Arcs, in 
introduced the German astronomers. e filar micrometer 
is here also treated, and the methods of celermunis the value 
of a revolution of the screw are discussed a t length. The 
investigation of the complete formula for posi eit the value 
of a revolution by observations upon a circumpolar star at its 
greatest elongation, is new. 
Chapter III, on Instruments for Measuring Time, embraces 
ocks, chronometers, and the electro-chronograph, the last being 
properly regarded as having the same relation to a clock that 
the micrometer has to the graduated circle. The performance 
ot the various chonographs most in use, is illustrated by full 
ized specimens of aie work at the Harvard College Observa- 
sae and other place 
fills St og of 150 pages. The student who makes himself 
master of all that this chapter contains on this, the primary and 
Sesemental instrument of the observatory, will be fully pre- 
} undertake the management of any other instrument, 
