education, as a matter of course. That the discovery was not sooner made supposes that something farther, and not of common occurrence was necessary; and this additional endowment appears to be the identifying power of similarity in general; the tendency to detect likeness in the midst of disparity and disguise. This supposition accounts for the fact, and is consistent with the known intellectual character of the inventor of the steam engine.” The Part Played by Imagination. A discoverer needs for success much more than identifying power. Professor John Tyndall, one of the chief expositors of science in the nineteenth century, speaks thus of the part played by an investigator’s imagination:-- “How are the hidden things of nature to be revealed? How, for example, are we to lay hold of the physical basis of light, since, like that of life itself, it lies entirely outside the domain of the senses? Now philosophers may be right in affirming that we cannot transcend experience. But we can, at all events, carry it a long way from its origin. We can also magnify, diminish, qualify, and combine experiences, so as to render them fit for purposes entirely new. We are gifted with the power of Imagination, and by this power we can lighten the darkness which surrounds the world of the senses. There are tories even in science who regard imagination as a faculty to be feared and avoided rather than employed. They had observed its action in weak vessels and were unduly impressed by its disasters. But they might with equal justice point to exploded boilers as an argument against the use of steam. Bounded and conditioned by co-operative reason, imagination becomes the mightiest instrument of the physical discoverer. Newton’s passage from a falling apple to a falling moon was, at the outset, a leap of the imagination. When William Thomson tries to place the ultimate particles of matter between his compass points, and to apply to them a scale of millimeters, he is powerfully aided by this faculty. And in much that has recently been said about protoplasm and life, we have the outgoings of the imagination guided and controlled by the known analogies of science. In fact, without this power, our knowledge of nature would be a mere tabulation of co-existences and sequences. We should still believe in the succession of day and night, of summer and winter; but the soul of Force would be dislodged from our universe; causal relations would disappear, and with them that science which is now binding the parts of nature into an organic whole.” Professor Tyndall also tells us how sound theories are divided from unsound:-- Theories Must be Verified.