the solar heat is actually produced in this way by the constant collision upon his surface of meteoric bodies, but for the particulars of this hypothesis we must refer to the book itself. Professor Tyndall opens the question in his volume respecting the share which different investigators have had in establishing the new theory of forces, and his observations have given rise to a sharp controversy in the scientific journals. The point in dispute seems to have been the relative claims of an Englishman and a German--Dr. Joule and Dr. Mayer--to the honor of having founded the new philosophy. Tyndall accords a high place to the German as having worked out the view in an _a priori_ way with remarkable precision and comprehensiveness, while he grants to the Englishman the credit of being the first to experimentally establish the law of the mechanical equivalent of heat. But his English critics seem to be satisfied with nothing short of an entire monopoly of the honor. The truth is, that, in this case, as in that of many others furnished us in the history of science, the discovery belongs rather to an epoch than to an individual. In the growth of scientific thought, the time had come for the evolution of this principle, and it was seized upon by several master-minds in different countries, who worked out their results contemporaneously, but in ignorance of the efforts of their fellow-laborers. But if individual claims are to be pressed, and each man accorded his aliquot share of the credit, we apprehend that America must be placed before either England or Germany, and for the explicit evidence we need look no farther than the volume of Professor Tyndall before us. The first clear connection and experimental proof of the modern theory was made by our countryman Benjamin Thompson,--afterwards knighted as Count Rumford by the Elector of Bavaria. He went to Europe in the time of the American Revolution, and, devoting himself to scientific investigations, became the founder of the Royal Institution of Great Britain. Davy was his associate, and, so far as the new views of heat are concerned, his disciple. He exploded the notion of caloric, demonstrated experimentally the conversion of mechanical force into heat, and arrived at quantitative results, which, considering the roughness of his experiments, are remarkably near the established facts. He revolved a brass cannon against a steel borer by horse-power for two and one-half hours, thereby generating heat enough to raise eighteen and three-fourths pounds of water from sixty to two hundred and twelve degrees. Concerning the nature of heat he wrote as follows, the Italics being his own:--"What is heat? Is there any such thing as an _igneous fluid_? Is there anything that with propriety can be called caloric? We have seen that a very considerable quantity of heat may be excited by the friction of two metallic surfaces, and given off in a constant stream, or flux, in _all directions_, without