Page:Collected Physical Papers.djvu/301

Rh The form of the response curve, stimulus remaining constant, is modified by the molecular condition of the wire. A wire in a sluggish condition shows feeble response, the recovery being also slow. The same wire after it has been vibrated for a time exhibits a stronger response. Longer time is required for recovery from the action of a stronger stimulus.

As already stated, when the clamp is put at the balancing position, alternate equal stimulations of A and B produce equal and opposite electromotive responses, and when the two ends are stimulated simultaneously there is no resultant effect.

Increased Excitability produced by Preliminary Vibration.—If now one-half of the wire, say the A half, be vibrated for a time, the electric excitability of that half will be found to be more or less permanently augmented, presumably by increased molecular mobility conferred by vibration. The response of A would now be found to be greatly enhanced, as compared with its previous response, the response of B remaining the same as before. If now both the ends are simultaneously vibrated, the previous balance will be found to be upset, the resultant showing that A in consequence of previous stimulation, has been rendered the more excitable.

If B be now vibrated for a time, the former approximate balance will be re-established by the enhanced responsiveness of B. Thus the following results