120 
SELF-RECOVERING COHERER 
Alkali Metals 
In the following investigations the radiator is a 
platinum sphere 97 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 excep 
tional 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 galvano 
meter 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 ener 
getically in one direction, indicating an increase of 
resistance : the receiver recovered instantaneously on 
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 automatic 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 resist 
ance, but with a gradual loss of power of auto 
matic recovery. This power was again restored on 
re-immersion of the coherer in kerosene. The re 
ceiver in vacuo, or under reduced hydrogen pressure, 
would have been preferred, had the necessary appli 
ances been available.