688 Sir J. J. Thomson on 



in the slab. Thus the velocity of the pulse through the' 

 medium containing the electrons will differ from that through 

 empty space and will depend upon the nature of the medium, 

 in spite of the fact that all the radiations which make up the 

 pulse travel with the velocity of light through a vacuum. 

 Hence we see that the constancy of the velocity of the mass 

 particles which carry the energy and mass of light is con- 

 sistent with light travelling with quite a different velocity 

 when passing through a refracting medium. 



On the view we are discussing the radiation as it were 

 carries its gether along with it. The medium which carries- 

 the radiation is not something uniformly distributed through 

 space but fragments torn from matter, carrying along with 

 them lines of electric force as an integral part of the 

 radiation. 



Though this theory of radiation may be described as an 

 emission one, yet since the velocity of the mass particles is 

 invariable the velocity of light will not be affected by the 

 motion of the source, or when the light is reflected, by the 

 speed of rotation of the mirror. Experiments recently made 

 by Majorana are in accordance with this result. 



Since on the view we are discussing energy is made up of 

 a number of equal units, the transference of energy from 

 one body to another must take place by definite steps, and 

 no transference is possible unless the amount to be trans- 

 ferred exceeds a finite amount. This involves that the 

 dynamics of processes involving very small transferences of 

 energy must differ fundamentally from ordinary dynamics. 



We are not yet in the position to calculate the mass of 

 one of these mass particles, but it is certain that it must be 

 an exceedingly small fraction of that of an electron. For 

 the energy ot an electron is about 10 ~ 7 erg, which can be 

 represented by the fall of the atomic charge of electricity 

 through about 6 x 10 4 volts. Now the average energy of a 

 molecule of a gas at 0° 0. corresponds to the fall of the 

 atomic charge through a potential difference of about ^ of 

 a volt. Hence if the mass of a mass particle is co times the 

 mass of an electron, the smallest amount of energy which 

 could be transferred from one body to another would be 

 about 1*8 x 10 6 x co times the mean energy of a gas molecule 

 at the temperature of 0° 0. Now suppose a gas is raised 

 from absolute zero to a higher temperature, if each molecule 

 of the gas receives the minimum amount of energy possible,, 

 the temperature of the gas would be raised to 



1-8x10 6 Xo>x273 absolute; 



