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Prof. J. C. Bose. On Electromotive Wave [May 21, 



with emery-paper. The wire so treated may, after, a long time, exhibit 

 partial recovery of its responsive power. 



The facts described above seem to show that the enhancement or 

 depression of response may, at least to a considerable extent, be due 

 to the increase or diminution of molecular mobility conferred by the 

 chemical reagents. With a given stimulus, the height of response 

 and the form of the response curve will be determined by the element 

 of molecular friction. In connection with this, it is instructive to 

 obtain records of the vibrations of a torsional pendulum, the friction 

 of which may be gradually increased by immersing the pendulum 

 more or less in a viscous fluid or sand. The various types of response- 

 curves in metals are found to be very similar to those thus obtained. 



Of these I give an interesting example. With moderate friction the 

 successive curves obtained with the pendulum are like those given in 

 the left of fig. 13 (a). With increased friction the height of the curve 

 is diminished, the maximum is reached later, and the recovery is pro- 

 longed (like the curve in the right of fig. 13 (a) ). With still greater 

 friction the recovery is arrested. 



(«). 



Fig. 13. — Photographic records showing the effect of " molecular arrest." The 

 two curves to the left of each set show the normal response; curve to the 

 right in (a) shows partial and in (b) complete arrest, produced by the reagent. 



It would appear as if the reagents which abolish response in metals 

 produce a similar molecular arrest. The following photographic 

 records seem to lend support to this view. If the oxalic acid be 

 applied in large quantities, the abolition of response is complete ; but 



