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74 Let us now take a tracing of a simple muscular contraction on a blackened surface moving with great rapidity. This is usually

done by causing the muscle to record its movement on a glass plate forming the bob of

a seconds pendulum which is allowed to make only one swing, and the tracing obtained is shown in this diagram. I found it was not easy to fit up such a pendulum in this lecture-room, and we shall therefore use the railway