382 Chauvenet’s Spherical and Practical Astronomy. 
the valuable material elsewhere given, but has contributed 
much original matter. The correction of a transit of the moon 
or a planet when the defective limb has been observed, which 
we have looked for in vain in treatises on practical astronomy, 
is here given in its proper place. The discussion of the proba- 
ble errors of transit observations is especially valuable. Soalso 
are the articles on the use of the portable transit instrument, 
both in the meridian and in the vertical circle of some circum- 
The author has not only digested into a complete system all 7 
made upon our Northwestern Boundary Survey is full of 
instruction to the young astronomer. h 
Criterion for the rejection of doubtful observations, is here very 
happily illustrated. Bessel’s method of reducing transits over 
several threads to a single instant, when the instrument is not 
in the meridian, first given in the Astronomische Nachrichten, 
vol. vi, is here for the time incorporated into a treatise as an 
essential part of the theory of the instrument. The author has 
simplified Bessel’s method, however, and given a new table 
which is obviously more convenient than the one given by 
Bessel for the same purpose. 
All the various practicable methods of determining the lati- 
tude by the transit instrument in the ‘prime vertical are sys- 
tematically deduced from a single fundamental formula and 
their several advantages brought out in a very clear manner, 
with the aid of full illustrative examples from actual observation. 
‘Finally, the method of determining the declinations of stars 
with the transit instrument in the prime vertical is given, 
together with the use of the micrometer in such determinations 
when the star passes very near to the zenith, a part of the sub- 
ject usually passed over in silence. 
Chapter VI, on the Meridian Cirele is likewise complete. 
The flexure of the telescope is considered. Formulas are given 
for correcting the observed declination of a planet’s limb, both 
for spheroidal figure and for defective illumination. These for- 
mulas are new, it being usual to allow for defective illumina 
tion upon the supposition that the planet is spherical. a 
Chapter VII, on the Altitude and Azimuth Instrument, is also 
a systematic digest of all that is valuable in this connection. For 
the reduction of observations over several horizontal threads, 
the instrument being slowly revolved in azimuth, a metho of 
vation practised at Greenwich with the Altazimuth, we see 
that the author gives a precise method instead of the roughone 
“Onan Vil pace 
_. Chapter , on the Zenith Telescope, ins in minute 
detail the method of employing this laenpaianats as practised 
upon the Coast Survey. We. that Mr. Chauvenet 
sages 
are not sure that Mr. C 
