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not influenced. Still we know that chemical changes are going on in this battery, and that these changes are followed by something we call a current of electricity. The best proof of this I can give you is that if I send this current round the wire covering the ends of the link of soft iron, you will find the properties of the soft iron altered so that it becomes powerfully magnetic. You observe that when no current is flowing, as is the case when I break the connection, the soft iron has no attractive influence on this piece of steel; but when I send the current on, at once the soft iron becomes so powerfully magnetic that it attracts the steel keeper with great force—a force so great that you see the keeper supporting a heavy weight. A wonderful change has been wrought in the soft iron—a change depending on molecular movements far too fine to come within the range of direct observation. It can be shown, however, that such a piece of soft iron actually elongates when the current passes round it, as in this experiment; and if I were to interrupt this current so as to send it at short intervals of time, the mass of soft iron would vibrate so as to give out a musical tone. It is not in my