Unlike Keely, Edison through all his years of experimental research has never once made a discovery. All the work of this great and successful inventor has been deductive, and the results achieved by him have been simply those of pure invention. Like Keely he constructs a theory, and works on its lines until he finds it untenable; then, he at once discards it and forms another theory. In connection with the electric light, he evolved or constructed three thousand successive theories; each one reasonable and apparently likely to be true; yet, only in two cases was he able to prove by experiment that his theories were correct. Of such a nature is the "dead-work" which all researchers on scientific principles must toil through to attain success. They must keep their minds open to every suggestion or idea, no matter how fanciful it may seem to others, and they must never let go their hold of it until it has been tested in all its possibilities. The same words which Lathrop uses, in describing Edison's characteristics, are equally applicable to Keely, who, in addition to his native endowment of a genius for science and mechanics, brings to bear vast patience in logical deduction, careful calculation, unlimited experiment, a ceaseless industry, and a persistence which refuses to be discouraged. Edison has said that he does not philosophize. Like General Grant, he is a man of action. When asked what theory he held upon a subject under discussion, General Grant replied, "I never theorize: when there is anything to be done, I do it." [12] Edison is always doing something which the public can see and appreciate, but, unlike Keely, he has no system to work out and transmute into the pure philosophy which is now revealing to the world "the further link in the chain of causation," "the cause of the cause," which hitherto has rather been assumed than demonstrated. "If we believe," says Professor Sir G. G. Stokes, "that what are called the natural sciences spring from the same supreme source as those which are concerned with morals and Natural Theology in general, we may expect to find broad lines of analogy between the two; and thus it may conceivably happen that the investigations, which belong to natural science, may here and there afford us hints with respect even to the moral sciences, with which at first sight they might appear to have no connection. And if such are to be found, perhaps they are more likely to be indicated by one whose studies have lain mainly in the direction of those natural sciences than by one whose primary attention has been devoted to moral subjects."