588 Prof. J. J. Thomson on the Emission of 



has important consequences when considered in relation with 

 the Second Law of Thermodynamics. For, consider an 

 enclosure at a constant temperature containing two sub- 

 stances in electrical connexion, one A giving at this tem- 

 perature a copious supply of corpuscles, the other B few, 

 if any : we see that we could utilize the stream of particles 

 from A so as to do mechanical work. But since everything 

 is at the same temperature, it follows from the Second Law 

 of Thermodynamics that the energy required for this work 

 cannot be derived from a lowering of the temperature of 

 any part of this enclosure: it cannot come from thermal 

 sources, but must come from some change in the state of the 

 working substance, presumably from some diminution in 

 the internal energy of the atoms of this substance. In- 

 vestigations made with the object of seeing whether prolonged 

 emission of corpuscles, such as might be produced by long- 

 continued incandescence, produces any appreciable effect on 

 the properties of the subject, might be expected to give 

 interesting results. There are undoubtedly changes produced 

 in a substance such as a piece of platinum wire by long- 

 continued incandescence, but we do not know as yet whether 

 these changes are such as indicate a change in the platinum 

 atom, or whether they are merely physical, such, for example, 

 as w r ould result from the expulsion of gases absorbed by the 

 wire. Again, many metals after the emission of corpuscles 

 by exposure to ultra-violet light show " fatigue/' i. e., the 

 rate of emission of corpuscles after long exposure becomes 

 less than it was initially : this is usually ascribed to the 

 formation or removal of films of gas or to a roughening of 

 the surface ; it is possible, however, that it may partly be due 

 to some change in the metal itself. Investigations on these 

 points would be of especial interest because, if the energy 

 of the corpuscles does come from changes in the atomic 

 energy, we have here a case in which this transmutation of 

 energy can be started and influenced by external conditions, 

 such as incandescence or the incidence of ultra-violet light 

 or Rontgen rays. 



On this view, the energy of the corpuscle emitted is not 

 derived directly from the work done on the corpuscles by the 

 electric field which exists in the Rontgen rays or in the light. 

 The rays act as detonators, causing some of the atoms on 

 wdiich they fall to explode, and the energy of the corpuscle is 

 derived from the energy liberated by this explosion. 



In the case of radium and other radioactive substances 

 we have probably also the transformation of internal atomic 



