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



B back to A, but not completely, and the negative deflection will be 

 less than the previous positive deflection. Owing to this " damping " 

 eftect, the oscillation curve will approximate to a logarithmic decrement 

 curve. After a series of reversals the oscillation dies away, and the 

 substance becomes almost inert. A glance at the hypothetical curve 

 to the right shows that at the inert stage, the .mhstance as a vjlwle 

 ought to become more conducting the fresh sj)ecimen, a. 



The opposite should ])e the case with negative substances (see 

 fig. 4 (a). 



Fig. 5 exhibits the actual curve obtained with a (compound) posi- 

 tive substance. 



Time of exposure. 



Fig. 5. — " Damped " Oscillation Curve for a Positive Substance. 



It is remarkable for its regularity. The next figure (fig. 6) gives 

 the curve for iron. The first diminution of resistance is too great to 

 be properly represented in the diagram. Here we have the same type 

 as in the previous case ; the inert stage, h, is also more conducting than a. 



lY. I will now consider the case of a negative substance exhibiting 

 damping ; arsenic will be taken as an example where the damping is 

 not so great as in the case of iron. 



Fig. 7 represents the actual curve obtained with arsenic (compare 

 with the hj^pothetical q\m\q for a negative substance, fig. 4 (a) ). 



It will be observed that the substance in the fatigued state is, on the 

 v:hote, Jess conducting than in the fresh condition, as we wei'e led to expect 

 from the hypothetical curve. It will also be seen that the oscillations 

 are very regular towards the end. The ciu-ves given in figs. 6 and 7 

 are those obtained with specimens immediately after they were set up. 

 Had I allowed them a period of rest to allow the particles to get pro- 

 perly settled, I would have got curves even more regular. It is, 

 however, evident that in substances exhibiting damping, two opposite 

 electric conditions are induced in fatigued specimens; the positive 

 becomes on the Avhole more conducting and the negative less con- 

 ducting than in the fresh specimens. At the inert stage the rate of 

 mutual conversion from one state to the other probably becomes equal, 

 and the apparent fatigue is thus not due to the absolute want of sensi- 



