Page:Elementary Text-book of Physics (Anthony, 1897).djvu/101

 particles, of such sizes and figures and with such other properties and in such proportion to space as most conduced to the end for which He formed them; and that these primitive particles, being solids, are incomparably harder than any porous bodies compounded of them, even so very hard as never to wear or break in pieces; no ordinary power being able to divide what God Himself made one in the first creation. . . . It seems to me, farther, that these particles have not only a vis inertiæ, accompanied with such passive laws of motion as naturally result from that force, but also that they are moved by certain active principles."

The science of physics has been erected upon the conception of the atom embodied in this description. It is not, however, a theory of the nature of the atom in any proper sense: any theory must explain the various properties ascribed to the atom on mechanical principles, with as few assumptions as are necessary to apply those principles. Such a theory was proposed by Thomson: it is known as the vortex atom theory. This theory assumes that the space occupied by the universe is filled with a continuous, incompressible, perfect fluid, and that each atom is a small closed vortex in this fluid. A comparison of the properties of the atom with those of the closed vortex, described in § 123, shows that the two sets of properties are identical. Thus the vortex, like the atom, retains its identity throughout any changes it may undergo, that is, it is not composed merely of matter in similar states of motion, but of identically the same matter at all times. No two vortices can cut each other or can occupy the same space at the same time; they are therefore indestructible and impenetrable. Furthermore, a vortex must move as a whole, and any two vortices near each other change their directions of motion as if they exerted force on each other. A vortex in which the vortex line is implicated or knotted any number of times will always retain the same degree of implication; so that if a vortex of a special sort be once set up, it will always retain its essential characteristics, corresponding to the retention of special characteristics by the atoms of the different elements. This theory, taken in connection with