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Rh six thousand times the weight of the earth of solid coal. With the quickness of genius he saw that we had here a power sufficient to produce the enormous temperature of the sun, and also to account for the primal molten condition of our own planet. Mayer shows the utter inadequacy of chemical forces, as we know them, to produce or maintain the solar temperature. He shows that were the sun a lump of coal it would be utterly consumed in five thousand years. He shows the difficulties attending the assumption that the sun is a cooling body; for, supposing it to possess even the high specific heat of water, its temperature would fall 15,000° in five thousand years. He finally concludes that the light and heat of the sun are maintained by the constant impact of meteoric matter. I never ventured an opinion as to the truth of this theory; that is a question which may still have to be fought out. But I refer to it as an illustration of the force of genius with which Mayer followed the mechanical theory of heat through all its applications. Whether the meteoric theory be a matter of fact or not, with him abides the honor of proving to demonstration that the light and heat of suns and stars may be originated and maintained by the collisions of cold planetary matter.

Let us now go back ten years and see how this verdict was arrived at.

When Professor Tyndall was preparing his work on heat, he desired to acquaint himself with all that Mayer had done upon this subject. He accordingly wrote to two eminent Germans, authorities upon this question, for information. Both responded, and one of them, Professor Clausius, procured Mayer's publications to send to Tyndall. In his first letter he said he thought Professor Tyndall would not find anything very important in Mayer's writings. But before forwarding the memoirs he read them himself, and then wrote to Tyndall: "I must here retract the statement, in my last letter, that you would not find much matter of importance in Mayer's writings; I am astonished at the multitude of beautiful and correct thoughts which they contain." He then went on to point out various important subjects in the treatment of which Mayer had anticipated other eminent writers. Professor Tyndall perfectly agreed with Clausius, and resolved to do his share toward making so able and original a man better known in England. Accordingly, on June 6, 1862, he gave a most interesting lecture at the Royal Institution, full of new views and novel experiments, on the subject of "Force." At its close he remarked: "To whom, then, are we indebted for the striking generalizations of this evening's discourse? All that I have laid before you is the work of a man of whom you have scarcely ever heard. All that I have brought before you has been taken from the labors of a German physician, named Mayer. Without external stimulus, and pursuing his profession as town physician in Heilbronn, this man was the first to raise the conception of the interaction of natural forces to clearness in his own mind. And yet he is scarcely ever heard of in scientific lectures, and even for scientific men his merits are but partially known. Led by his own beautiful researches, and quite independent of Mayer, Mr. Joule published his