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"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", changingthe motion from vertical to horizontal, and regulating the hand, the attachments of which are made to the metallic plate "i".
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