ling, but not for exact
observation. It has long been superseded by the _Aneroid_, which far
exceeds it in handiness.

[Illustration: FIG. 4.--Aneroid Barometer.]

_Aneroid Barometer._--Much obscurity surrounds the invention of barometers
in which variations in pressure are rendered apparent by the alteration in
the volume of an elastic chamber. The credit of the invention is usually
given to Lucien Vidie, who patented his instrument in 1845, but similar
instruments were in use much earlier. Thus in 1799 Nicolas Jacques Conte
(1755-1805), director of the aerostatical school at Meudon, and a man of
many parts--a chemist, mechanician and painter,--devised an instrument in
which the lid of the metal chamber was supported by internal springs; this
instrument was employed during the Egyptian campaign for measuring the
altitudes of the war-balloons. Although Vidie patented his device in 1845,
the commercial manufacture of aneroids only followed after E. Bourdon's
patent of the metallic manometer in 1849, when Bourdon and Richard placed
about 10,000 aneroids on the market. The production was stopped by an
action taken by Vidie against Bourdon for infringing the former's patent,
and in 1858 Vidie obtained 25,000 francs (L1000) damages.

Fig. 4 represents the internal construction, as seen when the face is
removed, but with the hand still attached, of an aneroid which differs only
slightly from Vidie's form. _a_ is a flat circular metallic box, having its
upper and under surfaces corrugated in concentric circles. This box or
chamber being partially exhausted of air, through the short tube _b_, which
is subsequently made air-tight by soldering, constitutes a spring, which is
affected by every variation of pressure in the external atmosphere, the
corrugations on its surface increasing its elasticity. At the centre of the
upper surface of the exhausted chamber there is a solid cylindrical
projection _x_, to the top of which the principal lever _cde_ is attached.
This lever rests partly on a spiral spring at _d_; it is also supported by
two vertical pins, with perfect freedom of motion. The end _e_ of the lever
is attached to a second or small lever _f_, from which a chain _g_ extends
to _h_, where it works on a drum attached to the axis of the hand,
connected with a hair spring at _h_, changing the motion from vertical to
horizontal, and regulating the hand, the attachments of which are made to
the metallic plate _i_. The motion o