3G4 Messrs. Trowbridge and Richards on the Temperature 



The conclusion that the large quantity of electricity, and 

 therefore the high temperature caused by the discharge, is 

 the cause of the very much diminished resistance of the tube 

 and the corresponding spectrum, leads us at once to consider 

 the energetics of the problem. On the assumption that the 



E 



departure from Ohm's law is not large*, since C= tp 



and the amount of impedance in the circuit is so small as to 

 be neglected, we shall have an amount of energy developed 

 in the tube for perhaps the millionth part of a second equal 

 to CE. With an electromotive force of 10,000 volts and a 

 resistance of ten ohms, a current of 1000 amperes must be 

 obtained, and this multiplied by 10,000 and divided by 746 

 gives the electrical horse-power if the current were maintained 

 ibr a second. The corresponding value is over 10,000, 

 and this corresponds to an excessively high temperature for 

 a very brief space of time. 



Of course a bolometer or any other thermometer in the 

 tube could not indicate this energy, for it is of very short 

 duration, and even in its brief existence undoubtedly does 

 not affect the whole mass of the gas through which the dis- 

 charge passes. J. J. Thomson has called attention to this 

 factf. In the case of the continuous discharge the tem- 

 perature is undoubtedly vastly lower, but even here it is 

 probable that the pale brush does not concern all the particles 

 of the rarefied gas, for otherwise the discharge in a wide 

 tube should be as bright as the discharge in a narrow tube. 

 Therefore calculations or experimental determinations of 

 the average temperature of a large tube, such as those of 

 Warburg % and Wood, while interesting as relative considera- 

 tions, give no clue as to the kinetic energy of the molecules 

 which actually carry the current. For such a clue one must 

 refer to experiments of the sort we describe. 



All the results recorded in this paper support the well- 

 known hypothesis that the current when disruptive is carried 

 by dissociated molecules. The continuous discharge is best 



* Moreover, we find that the electrostatic capacity of the Geissler tube 

 is not sufficient to affect the period of the oscillatory movement. To 

 decide this, we arranged a rocking key which interposed first the Pliicker 

 tube, and then, immediately afterwards, a wire of self-induction equal to 

 that of the tube, and photographed the oscillatory discharge through the 

 two circuits. No change could be perceived in the period of the two 

 discharges. If the electrostatic capacity of a Geissler tube were large, 

 an argon tube would not be so sensitive as it is to slight changes in the 

 electrostatic capacity in the circuit. 



t ' Recent Researches,' p. 167. 



X Wied. Ann. liv. p. 265. 



