458 Prof. J. C. Bose. On Electric Touch and tlie Molec^dar 



further and further, and the increase of resistance became less and less. 

 When the distance was increased to 25 cm. the action was reduced to 

 zero. When the distance was increased to 30 cm. there was a diminu- 

 tion of resistance, showing that 25 cm. is, in this case, the critical 

 distance. The receiver continued to exhibit a diminution until the 

 radiator was removed to a distance of 70 cm., when the radiation 

 intensity was too feeble to aftect the receiver. Now this critical 

 distance may approximately be regarded as a measure of the sensi- 

 bility of the substance. In this particular case the electric touch has a 

 negative sign. If by any means (some of which will be described 

 later on) the substance becomes more sensitive, i.e., more negative, the 

 critical distance will be increased. On the contrary, if the sensitiveness 

 becomes less (the substance tending towards positive direction) the 

 critical distance will be decreased. The application of this principle 

 is of importance as affording a means of determining the variation of 

 sensitiveness under different conditions. 



Experiments tuith Osmium Receiver. — Substances which are feebly 

 positive give a diminution of resistance when the radiator is close to 

 the receiver, and an increase of resistance when the radiator is beyond 

 the critical distance. Thus the critical distance for an osmium receiver 

 (whose normal action is moderately positive) was found to l)e about 

 250 cm. The radiator at a distance of 300 cm. produced a deflection 

 of - 3 divisions in a galvanometer placed in the receiver circuit. But 

 at the distance of 200 cm. the deflection became 4- 4, and at the 

 reduced distance of 50 cm. the deflection became -h 150 divisions. 



In order to avoid confusion, we may choose to call the efl'ect due to 

 strong intensity of radiation as the normal action. The sign of normal 

 action might further be verified, wherever possible, by obtaining a 

 reverse action with feeble radiation intensity. 



Molecular Changes produced in Matter hy the Action of Electric JVctves. 



A sensitive receiver made, say, of iron powder, has its conductivity 

 suddenly increased by the action of electric radiation ; but the sensi- 

 tiveness of the receiver is lost after the first response, and it is neces- 

 sary to tap it to restore the sensitiveness. On the theory of coherence, 

 the loss of sensitiveness is explained by supposing that electric radiation 

 brings the particles nearer and welds them together, and that the sen- 

 sitiveness can then only be restored by the mechanical separation of the 

 particles. This supposition, however, fails in the case of substances 

 ^vhieh exhibit an increase of resistance by the action of radiation. It 

 may, however, be supposed that by some process, little imclerstood, the 

 ]jarticles are sliglitly separated by the action of electric waves, thus 

 producing the observed increase of resistance. On this A'iew, however, 

 the restoration of sensitiveness by tapping remains unexplained. 



