The Pressure Gage. -A number of quartz plates suitably cut are arranged condenser fashion in a stack and introduced in an electric circuit. The quartz plates are subjected to the gas pressure to be measured by means of a piston. The combina tion of these constitutes a gage which is screwed into the wall of the gas chamber and the leads are brought out through holes drilled through the wall. The Recording Galvanometer. -A ballistic galvanometer whose period is long compared to the duration of

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... pressure phenomenon is connected to the electrodes of the quartz plates. The galvanometer deflections are photographically recorded on a rapidly moving film. The pressure-time curve is the differential of the recorded deflection-time curve.