It will also be noticed that whereas recovery is complete in 1 minute when the vibration amplitude is small, it is not quite complete within that time when the vibration amplitude is large. Greater strain prolongs the period of recovery. Owing to want of complete recovery, the base line is tilted slightly upwards. This slight displacement does not materially affect the results, provided the shifting is slight. From other records taken through a greater range of stimulation, it appears that in a curve obtained with electromotive variations as ordinates and amplitudes of vibrations as abscissae, the first part of the curve is, generally speaking, slightly convex to the abscissa (the convexity is pronounced when feeble stimulation gives negative response), it is then straight in the middle and concave in the last part. A limiting deflection is approached with high amplitude of vibration. The shape of the curve is modified by the molecular condition of the wire.
Maximum Effect.
If instead of a single vibration of a given amplitude we superpose a rapidly succeeding series, the individual effects are added up and a maximum deflection is produced which remains practically constant as long as the vibration is maintained. (A single ineffective stimulus may thus become effective by the additive effect of several.) Too long-continued vibration may cause fatigue, but during half a minute or so, the maximum effect is very definite (in tin). For a definite amplitude of vibration there is a definite maximum, which increases with the amplitude. For example, a single vibration of 5° gave a deflection of 3'5 divisions, the same when continued at the rate of four times per second gave a maximum deflection of eighteen divisions.
Again, with the same wire, a single vibration of 10° gave a deflection of 4'5 divisions, but continued vibration gave the definite maximum of 375 divisions. I give below a curve (fig. 10) which shows the maximum effect for different amplitudes of vibration.
Hysteresis.—Allusion has already been made as to the increased sensitiveness conferred by preliminary vibration. Being desirous of finding out in What manner this is brought about, I took a series of observations for an entire cycle, that is to say, a series of observations were taken for maximum effects, starting from 10° and ending in 100°, and backward from 100° to 10°. Effect of hysteresis is very clearly seen (fig, 10, A); there is a considerable divergence between the forward and return curves, the return curve being higher. On repeating the cycle several times, the divergence is found to be very much reduced, the wire on the whole is found to assume a more constant sensitiveness. In this steady condition, generally speaking, the sensitiveness for smaller amplitude of vibration is found to be greater than at the very beginning, but the reverse is the case for stronger intensity of vibration.
