Structure of the Universe 397" 



interstellar space where there was no planet or sun to attract it, it- 

 would remain suspended in space without motion, and would have na- 

 weight; but its mass would be the same as before. How is this? 

 Because it would require exactly the same amount of force to move- 

 it over a certain distance in a certain time. Mass is measured by 

 the amount of force required to move it over unit distance in unit 

 time, and unit mass is that quantity of mass which is moved unit dis- 

 tance in unit time by unit force, no matter in what part of the uni- 

 verse it may be placed, whether it may be on earth, or on the planet 

 Mars or Jupiter or billions of miles away in interstellar space. But 

 this only gives us a measure of mass. It does not tell us what mass 

 is. It is only in recent years by the study of X rays, cathode rays, 

 and other electrical discharges in the Crookes' tube that physical 

 science has been able to gain some definite knowledge on this subject. 

 Ag I stated in a previous part of this lecture, a good deal is now 

 known about the • behaviour of the particles, called electrons or cor- 

 puscles, which make up the discharge which passes from the negative 

 to the positive pole of the tube. The mass of these particles, the 

 electric charge which they carry, and the velocity with which they 

 travel have been measured. These particles may be called electric 

 points, or electric point charges, and it is found that their mass is 

 not a constant quantity, but that it varies with the speed with which 

 they travel in the tube. As their velocity is increased their mass' 

 becomes greater, as it is diminished their mass becomes less; so that 

 their mass is a function of their velocity. They have no mass apart 

 from motion. This being the case, their momentum is also a func- 

 tion of their velocity, as is also their energy, for momentum is the 

 product 01 mass and velocity and energy the product of mass and the 

 square of the velocity. I spoke about the electrons which whirl 

 around inside the system of the atom with very high velocities, in 

 some cases with nearly the velocity of light. Calculations have been 

 given by Sir J. J. Thomson showing the enormous amount of elec- 

 tronic energy due to the motions of the electrons inside the atomic 

 system. It is found that inside the atoms of one gram of hydrogen 

 gas there is contained an amount of electronic or corpuscular energy, 

 which if set free, would be sufficient to raise one million tons 300 feet 

 high. We know the energy which is liberated in an explosion of 

 dynamite or guncotton. That is atomic energy, caused by what we 

 call chemical affinity. But we see how much greater sub-atomic 

 energy is. Perhaps the day will come when man will know how to 

 set free this sub-atomic energy, but for the present it is probably bet- 

 ter that he does not know. 



'Negative Inequalities. 



The ordinary chemical atom, then, seems to be a sort of hole or 

 sink or hollow place in some medium which fills space, and to be a 

 locus or point into which pours tremendous energies from this 

 medium. This hole or sink or hollow place in space which is the 

 locus of the atom is what Reynolds calls a "negative inequality" in 

 the medium, or a "singular surface of misfit" due to a deficiency of 

 grains below the number in the regular normal piling in the sur- 



