from Long Vacuum Tubes. 743 



For example, with 20 amperes in the primary of the 

 transformer, a milliammeter (hot wire) showed that 25 

 milliamperes were flowing in the tube. If two small jars 

 were placed in parallel with the tube, the current rose at 

 once to 500 milliamperes, and a rotating mirror showed, 

 instead of the broad flares of light, corresponding to the 

 alternating potential, a large number of instantaneous dis- 

 charges, closely packed together, thirty or more to each 

 half cycle. The addition of more jars reduced the number 

 of these, the integrated current values increasing ail the 

 times, until with 10 jars only one instantaneous discharge 

 occurred for each half cycle, and the integrated current 

 strength was I'o amperes The integrated intensity of the 

 light emitted by the tube did not increase, however, to any 

 appreciable extent ; with the tube in the white stage it 

 actually decreased in fact. 



The condenser stores up energy as the potential rises from 

 the commencement of the half cycle until the terminal 

 potential on the tube reaches a value sufficient to cause a 

 discharge, the condenser emptying itself through the tube ; 

 this process is repeated over and over again during the period 

 of the half cycle, the hydrogen never becoming sufficiently 

 conducting to put the condenser out of action. 



In the case where the capacity of the condenser is such 

 that only one discharge occurs for each half cycle, calculation 

 shows that the instantaneous value of the current in the tube 

 is in the neighbourhood of three thousand amperes *. 



With argon in the tube the behaviour is quite different. 



With a capacity of seven leyden-jars the discharge is deep 

 violet in colour, a well-known characteristic of argon. With 

 the gas at a pressure sufficient to give a Crookes dark space 

 of 3 mm. and with a capacity of three small jars the 

 rotating mirror showed a most curious phenomenon. The 

 initial discharge of each half-cycle of the transformer was 

 instantaneous and of a deep violet colour. Following this 

 was a continuous " wing '' of light, similar in appearance to 

 the discharge without a condenser and of a light red colour. 

 This appears to indicate that the initial discharge of largo 

 current density (which gives the violet flash) increases the 

 conductivity of the argon to such a degree that the current 

 from the transformer passes freely through it without 

 charging the condenser, in other words the condenser is 

 thrown out of action. 



* My own estimate of the order of magnitude of the current w»a 

 confirmed by calculations made for me by Prof. G. W. Pierce, of 

 Harvard University. 



