1902.] accompanying Mechanical Disturbance in Metals. 275 



of light. The disturbance of molecular equilibrium caused by the 

 stimulus is attended by an electromotive variation, which gradually 

 disappears on the restoration of the molecules to equilibrium. The 

 rising portion of the response curve shows the electromotive effect, 

 due to stimulus, and the falling portion the recovery. The ordinate 

 represents the electromotive variation, and the abscissa the time. 



Experiments to Exhibit the Balancing Effect. 



If the wire has been carefully annealed, the molecular conditions of 

 different portions are approximately the same. Every portion of the 

 surface will be found nearly iso-electric. If the wire be held near the 

 middle by the clamp, and a vibration through an amplitude of, say, 90 " 

 be given to the end A, an upward deflection will be produced ; if a 

 vibration of 90° be given to B, there will be produced an equal down- 

 ward deflection. (Fig. 1, c) If both the ends are simultaneously 

 vibrated, the electromotive variation at the two ends will continuously 

 balance each other, and the galvanometer spot will remain quiescent. 

 (Fig. 1, d.) The clamp may even be removed, and the wire vibrated 

 as a whole ; the stimulation of A and B being the same, there will 

 be no resultant deflection. Having found the balancing point for 

 the clamp (which is at or near the middle), if the clamp be now shifted 

 to the left, on simultaneous vibration of A and B, the A effect will be 

 relatively stronger (inasmuch as the angular vibration of A is increased 

 and that of B decreased), and there will be produced a resultant upward 

 deflection. Thus keeping the rest of the circuit untouched, by merely 

 moving the clamp from the left, past the balancing position to the 

 right we get either a positive or zero or a negative resultant effect. 

 This can be repeated any number of times. The experiment shows 

 further that when the amplitude of vibration is kept constant, the 

 intensity of electromotive effect is increased by shortening the wire. 

 A thick wire produces a stronger response. The direction of the 

 current of response in the wire is in the majority of metals under 

 normal condition, from the relatively less to the relatively more 

 excited point. 



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 is also slow. The same 

 wire after it has been vibrated for a time exhibits stronger response. 

 The period of recovery may also then be hastened. Longer time is 

 required for recovery from the effects of a stronger stimulus. 



Comparison of Electric Excitability of Tivo Points by the 

 Method of Balance. 



As has already been said, when the clamp is put at the balancing 



U 2 



