For this purpose water manometers have hitherto been employed; but,
although the indications given by these are very accurate, their form
and weight are such as to render them not easily transportable; and
then, again, considerable care is necessary in putting them in place.
Mr. Brouardel's registering manometer does not give so accurate
indications, perhaps, but it possesses, as an offset, the merit of being
very portable and easily put in place; and, besides, it inscribes the
hour at which the pressure is exerted.
The apparatus consists of a metallic cylinder, A B, which carries a
circular shoulder, C, that rests on a plate, D--the latter being put in
motion by a clock which is wound up by means of a button under the base,
E, of the apparatus. The two standards, F F, carry a crosspiece which
supports a disk that closes freely the aperture of the drum, A B, in
such a manner as not to impede its rotation.
In the interior of the cylinder there is a metallic cup which is
connected with the central reservoir by an impermeable membrane, I.
These three parts form a closed chamber, into which the pressure comes
through a tube, F, provided with a cock. A spring, M, which counteracts
the pressure, is arranged between the crosspiece, G, and the bottom of
the reservoir.
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