Page:Popular Science Monthly Volume 76.djvu/275

Rh essentially the same. Indeed in some respects the older view has the advantage, as it lays greater stress upon the motion of the atoms; a forecast of the modern kinetic theory of matter.

The lack of development of the atomic theory is to be ascribed largely to the adverse criticism of Aristotle. The overwhelming influence of the Aristotelian philosophy was thrown against it, and it made little headway down through the middle ages. Not until the downfall of scholasticism do we find any extensive revival of the system; a revival culminating in the seventeenth century school of atomists, among whom are to be noted Gassendi, Boyle and, as we have seen, Newton. But still another century of stagnation was to elapse before it was to be transformed and modernized at one stroke by the genius of the English chemist John Dalton.

The modern atomic theory founded by Dalton and developed during the nineteenth century must not be regarded merely as an extension of the older theory, but as a new structure built upon the old one as a foundation. That was speculative, this was scientific. That was vague, this was definite. That was based merely upon observation and introspection, this upon experiment and calculation. The theory of the elements and the theory of atoms was blended into a single comprehensive whole. The prime distinction between the different kinds of atoms was found in a single property—that of their relative mass. The older theory was not inadequate in the early days of science; but it failed when the quantitative relations of phenomena were brought into prominence by the development of experimental methods; and such was the case when the principle of the indestructibility of matter was raised by Lavoisier from a philosophic dogma to a scientific truth, and emphasis was thus laid upon mass as the fundamental property of matter.

I need not detail to you the marvelous growth of the theory during the past century; how it met every demand made upon it by modern chemistry, and indeed inspired much of the development of that 6cience; how, on the other hand, it has lent its aid to the progress of physics and especially how by the founders of the kinetic theory of gases,

 the flaring atom streams And torrents of her myriad universe Ruining along the illimitable inane

were marshaled to the defense of the great principle of the conservation of energy, and the science of heat was annexed to the domain of mechanics. Let me rather recall to you the salient points of the theory as held by the close of the century, for comparison on the one hand with the theory of the past and on the other with its developments in the future.