Page:On the light thrown by recent investigations on Electricity on the relation between Matter and Ether.djvu/17

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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 etherial mass attached to the atoms; on this view the diminution in the etherial 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 developed by their chemical combination. As an example, let us take the case of the chemical combination which of all those between ordinary substances is attended by the greatest evolution of heat, that of hydrogen and oxygen. The combination of hydrogen and oxygen to form one gramme of water evolves 4000 calories, or 16.8 x 1010 ergs, the mass which moving with the velocity of light, i.e., 3 x 1010 centimetres per second possesses this amount of kinetic energy is 3.7 x 10-10 grammes, and this therefore is the diminution in the etherial mass which takes place when oxygen and hydrogen combine to form 1 gramme of water; as this diminution is only about one part in 3000 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 gramme of radium gives out during its life an amount of energy equal to 6.17 x 1016 ergs, if this is derived from the electric potential energy of the radium atoms, the atoms in a gramme of radium must possess at least this amount of potential energy, they must therefore have associated with them an etherial mass of between one-eighth and one-seventh of a milligramme, for this mass