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vanometer moves to the right, and if I heat the other it moves to the left. We now place this one, which causes a deflection to the right when it becomes hot, in connection with a muscle to which a weight is attached, and we place the nerve of the muscle over the two wires from the secondary coil of our induction Fig. 58.—Diagram showing the arrangement of the apparatus in the demonstration of the heat of muscular contraction, a, case with sides of thick plate glass; b b′, thermal piles; b, galvanometer element; d, key; e, primary and f secondary coil. The contents of the glass case are seen on a large scale in next figure. The galvanometer has a low resistance. machine. To keep off all radiant heat as much as possible, we shall enclose the whole apparatus in a square chamber, the walls and roof of which are made of plate glass one inch in thickness. Notice the position of the spot of light. I now open the key so as to tetanise the muscle, and you notice that at once the