what is known as "periodic acceleration," pulsation or vibration. We can not measure a uniform motion in a particle moving with the speed of light, but we can measure its acceleration. All forces pulsate; they are all propagated as waves, which set up vibratory motions in matter and thus make their presence evident.
In support of this statement about the nature of mass, which is of such fundamental importance, the words of Professor Rutherford may be quoted:
If a charge of electricity in motion exactly simulates the properties of mechanical mass, it is possible that the mass of.matter in general may be electrical in origin and may result from the movement of the electrons constituting the molecules of matter.
It is to be noticed that Professor Rutherford refers to the electrons as charges of electricity. His words give a full, if concise, definition of the electrical theory of matter which is accepted by the mass of physicists and of which Sir Oliver Lodge is the able historian. When Davy suggested that matter and electricity were kindred phenomena he could hardly have suspected how near he was to the truth as it is seen to-day. The materialists and energists are now on the high-road to reconciliation, and we are permitted to feel that an explanation may soon be forthcoming for the well-known relation between specific heat and atomic weight, and for that existing between spectral phenomena and atomic weight.
The matter of gravitation can not be put aside without a few additional remarks. Lord Kelvin, by calculation, has ascribed to the ether a weight of one-thousand-billionth of a gram per cubic meter. This is not very much, and can give little encouragement to Lothar Meyer's suggestion that the slight divergences between theoretical and actual atomic weights in the periodic system may be due to the imprisonment of a quantity of the ether within matter; as just suggested, these differences are more likely due to electronic losses.
If the new theory of mass is accepted we must postulate a quantity of energy in the ether in keeping with its weight. We shall know more about this when these quantities have been calculated by different indirect methods and the results compared. We shall have occasion, a little later, to discuss the temperature of space between which and its internal energy and mass some relation may exist. Heat is usually considered to be due to atomic agitation; we are now assuming mass to be due, possibly, to corpuscular agitation, which already produces, as we know, light and other electro-magnetic phenomena. The day may come when, able to control the internal forces of the atom and effect transmutations, man may set about destroying matter, as such, altogether, for use in his industries at so much per kilowatt-hour. To the peculiar forms of insanity which induce some men to sell eternal salvation and others
