ter and could be released from the atom by a variety of agencies. This idea was much widened and strengthened by the investigations of Zeeman and Lorentz, who showed that the radiation of light must be mainly ascribed to the movements of electrons of the same small mass within the atom.
It does not fall within the scope of my address to outline the very important consequences that followed in many directions from this fundamental discovery of the independent existence of the electron and its connection with matter. It was found by Kaufmann that the mass of the electron was not a constant but increased with its speed, and from this result it was deduced that the electron was an atom of disembodied or condensed electricity occupying an exceedingly small volume, whose mass was entirely electrical in origin.
Unit of Electricity
I should mention here one important consequence that has followed from these discoveries. From the laws which control the passage of electricity in conducting solutions, Faraday recognized that there must be a close connection between the atom of matter and its electrical charge. Maxwell and Helmholtz suggested that the results were simply explained by supposing that electricity was atomic in nature. This conclusion is now definitely established, and the positive charge carried by the hydrogen atoms in the electrolysis of water is believed to be the fundamental unit of electrical charge. This charge is equal to and opposite to the charge carried by the electron. Any charge of electricity, however small or large, must be expressed by an integral multiple of this fundamental unit of electricity. The actual value of this unit charge has been measured by a great variety of methods and with concordant results. One of the most detailed and accurate investigations of this important constant has been made by Professor Millikan, of the University of Chicago.
Objections to the Atomic Theory
We have so far implicitly assumed that the great majority of scientific men now regard the atomic theory not only as a working hypothesis of great value but as affording a correct description of one stage of the sub-division of matter. While this is undoubtedly the case to-day, it is of interest to recall that less than twenty years ago there was a revolt by a limited number of scientific men against the domination of the atomic theory in chemistry. The followers of this school considered that the atomic theory should be regarded as a hypothesis, which was of necessity unverifiable by direct experiment and should, therefore, not be employed as a basis of explanation of chemistry. This point of view was much strengthened by the recognition of the power of thermodynamics in affording a quantitative explanation of the
