MATTER AND ETHER THOMSON. 237 



with it may be expected to have very different properties from ordi- 

 nary matter ; it would of course defy chemical analysis and probably 

 w^ould not be subject to gravitational attraction, it is thus a very in- 

 teresting problem to see if we can discover any case in which the 

 ethereal mass is an appreciable fraction of the total mass, and to com- 

 pare the properties of such a body with those of one whose ethereal 

 mass is insignificant. Now in any ordinary electrified system, such 

 as electrified balls or charged Leyden jars the roughest calculation is 

 sufficient to show that the ethereal mass which they possess in virtue 

 of this electrification is absolutely insignificant in comparison with 

 their total mass. Instead, however, of considering bodies of appre- 

 ciable size let us go to the atoms of which these bodies are composed, 

 and suppose, as seems probable, that these are electrical systems and 

 that the forces they exert are electrical in their origin. Then the 

 heat given out when the atoms of different elements combine will be 

 equal to the diminution of the mutual electrostatic potential energy 

 of the atoms combining, and therefore by what we have said will be 

 a measure of the diminution of the ethereal mass attached to the 

 atoms ; on this view the diminution in the ethereal mass will be a mass 

 which moving with the velocity of light possesses an amount of 

 kinetic energy equal to the mechanical equivalent of the heat de- 

 veloped by their chemical combination. As an example, let us take 

 the case of the chemical combination which of all those between ordi- 

 nary substances is attended by the greatest evolution of heat, that of 

 hydrogen and oxygen. The combination of hj^drogen and oxygen to 

 form 1 gram of water evolves 4,000 calories, or 16.8X10^" ergs, the 

 mass which moving with the velocity of light, i. e., 3X10^° centimeters 

 per second possesses this amount of kinetic energy is 3.7X10^** grams, 

 and this therefore is the diminution in the ethereal mass which takes 

 place wiien oxygen and hydrogen combine to form 1 gram of water; 

 as this diminution is only about 1 part in three thousand million of 

 the total mass it is almost beyond the reach of experiment, and we 

 conclude that it is not very promising to try to detect this change in 

 any ordinary case of chemical combination. The case of radio-active 

 substances seems more hopeful, for the amount of heat given out by 

 radium in its transformations is enormously greater weight for 

 weight than that given out by the ordinary chemical elements when 

 they combine. Thus, Professor Rutherford estimates that a gram of 

 radium gives out during its life an amount of energy equal to 

 6.17X10^" ergs, if this is derived from the electric potential energy of 

 the radium atoms, the atoms in a gram of radium must possess at least 

 this amount of potential energy, they must therefore have associated 

 with them an ethereal mass of between one-eighth and one-seventh 

 of a milligram, for this mass if moving with the velocity of light 

 would have kinetic energy equal to 6.7X10^*^ ergs. Hence, we con- 



