168 Prof. J. C. Bose. On a Self-recovering Coherer and the 



or thirty flashes, however, the receiver lost its power of automatic 

 recovery, and the sensitiveness had then to be restored by tapping. 

 An interesting observation was made to the effect that on the last occa- 

 sion the receiver responded without previous tapping, a rumbling noise 

 was heard in the telephone which lasted for a short time, evidently due 

 to the re-arrangement of the surface molecules to a more stable condi- 

 tion, after which the power of self-recovery was lost. 



The state of sensibility described above is more or less transitory, 

 and is induced, generally speaking, by a somewhat unstable contact 

 and low E.M.F. acting in the circuit. In the majority of metals, the- 

 normal tendency is towards a diminution of contact resistance by the- 

 action of electric waves. The occasional increase of resistance, in 

 general, disappears when the pressure and E.M.F. are increased. But 

 in the case to be presently described we have an interesting exception,, 

 where the normal state of things is just the reverse of what prevails in. 

 the majority of metals. 



Alkali Metals. 



In the following investigations the radiator is a platinum sphere 

 9*7 mm. in diameter. The coherer was placed at a short distance, so 

 that the intensity of incident radiation was fairly strong. 



Potassium. — In working with this metal, the exceptional nature of 

 the reaction became at once evident. The effect of radiation was to 

 produce an increase of resistance. The pressure of contact was adjusted 

 till a current flowed through the galvanometer, the galvanometer spot 

 of light being at one end of the scale. On subjecting the receiver to* 

 radiation the spot of light was deflected to the opposite end, exhibiting 

 a great increase of resistance. When the pressure and E.M.F. were 

 suitably adjusted a condition was soon attained, when a flash of 

 radiation made the spot of light swing energetically in one direction, 

 indicating an increase of resistance : the receiver, however, recovered 

 instantaneously with the cessation of radiation, and the spot violently 

 swung back to the opposite end, indicating the normal current that ^ 

 flows in the circuit. This condition was found to persist, the receiver 

 uniformly responding with an increase of resistance followed by auto- 

 matic and instantaneous recovery. To prevent oxidation, the receiver 

 was kept immersed in kerosene. When the receiver was lifted from 

 the protecting bath, it still continued to respond with an increase of 

 resistance, but with a gradual loss of power of automatic recovery* 

 This power was again restored on again immersing the coherer in 

 kerosene. The receiver in vacuo, or under reduced hydrogen pressure,, 

 would have been preferred, had the necessary appliances been available. 



Sodium. — As we pass from potassium to the neighbouring metals, 

 there is a gradual transition of property as regards the nature of 

 response to electric waves. With sodium the adjustment is a little 



