1901.] 



between Radiation and Mechanical Strains. 



181 



7. Effect of Summation of Stimuli. . 



In the case of effect of rapidly succeeding flashes of electric radia- 

 tion on Ag', it was shown (see fig. 14) that the partial effects were 

 fused together and there was produced a limiting effect, kept balanced 

 by the force of restitution. With rapidly succeeding mechanical 

 stimuli, we again obtain an exactly similar result. Fig. 15 (a, b) shows 

 the effect of continuous vibration on tin cell, with different intensities 

 of vibration, the vibration-frequency being two in a second. The 

 eurve gradually rises and attains a maximum, at which position it is 









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Fig. 14. — Effect of continuous vibration, (a) and (b) show effects on a Tin cell. 

 In (c) the effect on the particular Silver cell ; the sign of E.M. variation is 

 opposite to that of Tin cell, (d) shows the effect on a Nickel cell. 



held almost rigid as long as the disturbance is kept up. But on the 

 stoppage of vibration there is an immediate recovery, and if sufficient 

 time be allowed the recovery is complete, as seen in the last curve of 

 the series. The disturbance was kept up for 1 minute, and the period 

 ■of recovery allowed was also 1 minute. In this way I obtained a 

 long-continued series of exactly similar curves, there being little 

 fatigue ; this is the case when a period of repose intervenes. But if 

 the vibration is kept up without intermission signs of fatigue begin 

 to appear, and the curve tends to fall. In some metals there may 

 even be a reversal. Observe the flat top of the curve similar to that 

 of Ag' under electric stimulus mentioned above. Also the effects of 

 different intensities of vibration, as shown in (a) and (b). 



In (d) is shown the effect of vibration on Ni. After reaching the 

 maximum there is a tendency towards reversal. Ni also shows 

 greater signs of fatigue. 



