whither will all this discussion of relativity lead us, and what is the chief end and aim and hope of those interested in the relativity theory. The answer will depend upon the point of view. To the mathematician the whole theory presents a consistent mathematical structure, based on certain assumed or demonstrated fundamental postulates. As a finished piece of mathematical investigation, it is, and of necessity must remain, of theoretical interest, even though it be finally abandoned by the physicists. The theory has been particularly pleasing to the mathematician in that it is a generalization of the Newtonian mechanics, and includes this latter as a special case. Many of the important formulas of the relativity mechanics, which contain the constant denoting the velocity of light become, on putting this velocity equal to infinity, the ordinary formulas of the Newtonian mechanics. Generality is to the mathematician what the philosopher's stone was to the alchemist, and just as the search for the one laid the foundation of modern chemistry, so is the striving after the other responsible for many of the advances in mathematics.
On the other hand, those physicists who have advocated the theory of relativity see in it a further advance in the long attempt to rightly explain the universe. The whole history of physics, is, to use a somewhat doubtful figure of speech, strewn with the wrecks of discarded theories. One does not have to go back to the middle ages to find amusing reading in the description of these theories, which were seriously entertained and discarded only with the greatest reluctance. But all the arguments of the wise, and all the sophistries of the foolish, could not prevent the abandoning of a theory, if a few stubborn facts were not in agreement with it. Of all the theories worked out by man's ingenuity, no one has seemed more sure of immortality than the one we know as the Newtonian mechanics. But the moment a single fact appears which this system fails to explain, then to the physicist with a conscience this theory is only a makeshift until a better one is devised. Now this better one may not be the relativity mechanics—its opponents are insisting rather loudly that it is not. But in any case, the entire discussion has had one result pleasing alike to the friends and foes of relativity. It has forced upon us a fresh study of the fundamental ideas of physical theory, and will give us without doubt, a more satisfactory foundation for the superstructure which grows more and more elaborate.
It can well happen that scientists, some generations hence, will read of the. relativity mechanics with the same amused tolerance which marks our attitude towards, for example, Newton's theory of fits of easy transmission and reflection in his theory of the propagation of light. But whatever theory may be current at that future time, it will owe much to the fact that in the early years of the twentieth century, this same relativity theory was so insistent and plausible, that mathe-
