470 Prof. J. C. Bose. On Electric Touch and the Molecular 



Restoration of Sensitiveness to a Fatigued Substance. 



It was said that the inertness of the substance, after long exposure,, 

 is due to the presence of a relatively large amount of strained B variety. 

 It therefore follows that if by any means we can transform B into A, 

 then after such a transformation there ought to be a restoration of 

 the sensitiveness. It has also been stated that the B variety under 

 ordinary circumstances is less stable than A. If now we apply a 

 disturbing cause which is unilateral in its action — that is to say, if it 

 converts B into A and not A into B — then such a disturbing cause 

 will resensitise the fatigued substance. 



Effect of Mechanical Disturbance. — Of the unilateral actions, mechani- 

 cal vibration is one ; for it is known that by the action of friction a 

 substance may pass from one modification to another in one direction 

 only. Thus the change of monoclinic into rhombic variety of sulphur 

 is hastened by scratching with a glass rod, but the change does not 

 take place in the opposite direction. We may now apply the crucial 

 tests. Mechanical vibration will transform B into A, and with posi- 

 tive fatigued substances this ought to produce an increase of resistance 

 (as A is less conducting than B) ; with negative substances the same 

 disturbance ought to produce a diminution of resistance. 



Effect of Heat. — There are other methods by which the B variety 

 may be transformed into A ; the more subtle molecular disturbance due 

 to heat may be expected to be even more effective in producing the 

 transformation. Here, too, the crucial test is that by slight heating the 

 fatigued positive substance ought to show an increase of resistance,, 

 and the negative substance a diminution of resistance. The two 

 following curves (figs. 8 and 9) confirm in a remarkable manner my 

 anticipations. 



Effect of Heat and Mechanical Disturbance on ct Positive Fatigued Sub- 

 stance. — I shall at first deal with the curve for iron. At the end of 

 No. 6 curve, the substance was left in the inert stage b. While in this 

 state, the receiver was heated to a slight extent. Observe in the 

 dotted portion of the curve the sudden fall of conductivit}^ (increase 

 of resistance). I should like to say here, that, though the fall has 

 been indicated by a straight line, as representing the somewhat sudden 

 fall of conductivity, I sometimes noticed on careful inspection a slight 

 oscillatory movement of the galvanometer spot during this process. 

 The significance of this I will notice on a future occasion. The ulti- 

 mate eff'ect of slight heating (excess of heat produces other complica- 

 tions) is the restoration of the original reduced conductivity. If the 

 application of heat transforms B into A, we may expect the substance 

 to regain its sensitiveness, which it lost in the fatigued stage b. The 

 receiver was now exposed to radiation, and it at once responded, 

 exhil)iting almost its original sensibility. Observe how the subsequent 



