A writer speaks of a special form of the barometer, used generally by
travelers, in which air supplies the place of mercury as a measuring
medium. Speaking of its use, he says:
As the pressure of the outside air varies does it rise and
fall, and by a beautifully delicate apparatus this rising
and falling is magnified and represented upon the dial. Such
barometers are made small enough to be carried in the pocket,
and are very useful for measuring the heights of mountains; but
they are not quite so accurate as the mercurial barometer, and
are therefore not used for rigidly scientific measurements; but
for all ordinary purposes they are accurate enough, provided
they are occasionally compared with a standard mercurial
barometer, and adjusted by means of the watch-key axis provided
for that purpose, and seen on the back of the instrument. They
are sufficiently delicate to tell the traveler in a railway
whether he is ascending or descending an incline, and will
indicate the difference of height between the upper and lower
rooms of a three-story house. The unseen air in the aneroid is
a mark of the rise or fall in altitude of the possessor of the
instrument.
Conscience plays a like part in morals. It is always with us and always
admonishes us of the varying moral altitudes to which we rise or fall.
(542)