Oscillograph

—An instrument for determining the form of alternating current waves. It is in reality a galvanometer having a moving system capable of extremely rapid vibration, fitted with a suitable arrangement for recording the vibrations. The deflection at any instant is practically proportional to the current flowing through it at that instant, in spite of the fact that the current may be varying very rapidly in strength and direction. It must be critically damped, as any tendency to overshoot would distort the wave form from its true shape. A new use for the oscillograph is found in the q investigation of the oscillations which occur when switching off a continuous current in an inductiong le circuit. A record is obtained photographically showing most clearly simultaneous variations of different amplitudes. It is suggested that valuable application of the oscillograph to wirele telegraphy may be made in this way.