628 Professor Jagadis Chunder Bose [May 10, 



But if to be<nn with, the two were not in the same molecular condition, 

 an initial P.D. would exist between them, and then, owing to the difference 

 in the anodic and kathodic sensitiveness, the responses given by the two 

 would not be identical. 



Usually I interpose an external resistance varying from one to five megohms 

 according to the sensitiveness of the wire. The resistance of the electrolyte 

 in the cell is thus relatively small, and the galvanometer deflections are pro- 

 portional to the E. M. variations. It is always advisable to have a high 

 external resistance, as by this means one is not only able to keep the deflec- 

 tions within the scale, but one is not troubled by minute accidental disturb- 

 ances. 



When the eel! is freshly made, the wires, owing to the strain set up 

 during the mounting, may exhibit slightly erratic responses. Both should 

 then be short-circuited, and after being subjected to vibrations for a time, the 

 cell should be allowed a short period of rest. In this way, after a little prac- 

 tice, it is always possible to bring the response to a normal condition. The 

 responses subsequently obtained become extraordinarily consistent. There is 

 no reason why perfect results should not be arrived at, if these conditions are 

 fulfilled. 



If now a rapid torsional vibration be given to A 

 Application (or B), there will be induced an electromotive 

 of Stimulus. variation. The intensity of stimulus is increased 



with the amplitude of vibration. Greater intensity 

 of response is always obtained with greater intensity of stimulus. 



Considerations showing that Electric Response is due to Molecular Dis- 

 turbance. — 1. The electromotive variation varies with the substance. With 

 superposition of stimuli, a relatively high value is obtained in tin, amounting 

 sometimes to nearly half a volt, whereas in silver the electro-motive variation 

 is only about - 01 of this value. The intensity of the response, however, 

 does not depend on the chemical activity of the substance, for the electro- 

 motive variation in the relatively chemically-inactive tin, and even gold, is 

 greater than that of zinc. Again, the sign of response in silver, positive or 

 negative, depends on its molecular condition.* 



2. It may be thought that the electro-motive variation is due to some 

 thermo-electric eflect, inasmuch as the wire may be heated by vibration. The 

 heat produced by a single vibration, however, must be very small. In order 

 to test whether heating of the wire would produce effects comparable in mag- 

 nitude to that produced by vibration, I made a cell with lead wire (the 

 external resistance interposed in the circuit was 100,000 ohms). On subjecting 

 one wire to the heating action of concentrated light from an arc lamp, during 

 a continuous exposure of one minute, the effect on the galvanometer was a 

 deflection of barely one division of the scale. But when the same wire was 

 subjected to five quickly succeeding vibrations, lasting altogether only a few 

 seconds, there was produced the very large deflection of 180 divisions. 



Numerous other effects will be described presently which cannot be ex- 

 plained on the thermo-electric theory of action. I find for instance that the 



* It is curious to note that the response of silver tilings to Hertzian waves 

 also depends on the molecular condition of the silver. In one condition there is 

 produced a diminution of resistance, or positive effect: in the other the resistance 

 is increased, i.e. the effect shown is negative. (See my Paper on " Electric 

 Touch," Proc. Roy. Soc, Aug. 1900.) 



