250 Prof. J. Lovering on the Aneroid Barometer. 
navigator and the student of general science should know what 
degree of accuracy may be claimed for the new barometer and 
how far they are allowed to trust themselves to its indications. 
With the hope of assisting those who desire to form an opinion 
on this subject, [ present the following experiments and observa- 
tions, undertaken originally at the suggestion of Prof. A. D. Bache, 
Superintendent of the U.S. Coast Survey. The instrument em- 
ployed in this research was furnished by Prof. Bache, and bears 
the mark 1265, Lerebours and Secretan, Paris. 
A series of experiments was first made with this aneroid ba- 
rometer to determine the whole range of the instrument. For 
this purpose, it was placed first under the receiver of an exhaust- 
ing pump, and afterwards under the receiver of a condensing 
engine. In this way, it was found capable of indicating a change 
of atmospheric pressure which would move the column of mer- 
cury in acommon barometer from about twenty inches up to 
thirty-one inches. From the nature of its construction, the index 
cannot go beyond the point which corresponds to twenty inches 
of the mercurial barometer on one side, or that which corresponds 
to thirty-one inches of the same on the other. How accurately 
its march between these limits agrees with that of the mercurial 
moves farther than the column of mercury under the same change 
atmospheric pressure. As it approaches its lower limit, how- 
ever, it will begin of course to be restrained in the amplitude of 
its motion, until, at length, the difference between the two instru- 
ments changes its sign. It is obvious that, in the partitular in- 
those of the pump-gauge to within ‘Ol of an inch. Such is the 
statement in the London Atheneum, although I find no mention 
