Having given an idea of the coarse-grainedness of matter, Thomson proceeds to consider the various theories of that structure, and gives an account of the most important of these by Lord Kelvin and Lindemann. Rücker in 1888, are then explained, and the limits of molecular action deduced from these experiments. The results of the well-known researches of Quincke on silver films and on capillary elevation, as summarized in a lecture delivered before the Chemical Society of London by Prof. must be comparable with the range of molecular action of the water molecules. The discussion of the methods by which the limit is reached in the case of surface tension is next clearly given, and the result arrived at that a thickness of 10 -8 cm. surface-tension, the difference of potential which occurs when two metals are placed in metallic connection, the amount of polarization at the surface of an electrode and of an electrolyte, and the viscosity, the diffusion, and the conductivity for heat, of gases. These conclusions are founded upon considerations of several distinct sets of phenomena, viz. Lord Kelvin, Loschmidt, and others have gone still further, not only proving that matter possesses structure, but giving limits below which the “coarse-grainedness” of matter cannot lie. But this attempt was an incomplete one, and a less ambiguous proof was given by Osborne Reynolds in 1879, based upon the thermal effusion of gases. The first attempt was made by Cauchy, founded on the dispersion which light experiences when it passes through transparent bodies. Thomson briefly but clearly explains the historical development of this proof. And although the theory of the molecular constitution of matter now universally held has been adopted as regards chemical change ever since the publication of Dalton's new system of chemistry in 1808, the crucial proof of its necessity has only recently been given. It is from the interpretation of chemical phenomena, by the help of exact physical research, that we may most hopefully look for insight into the true explanation of these phenomena. Thomson, of Cambridge, on the theories of the molecular structure of bodies. Amongst the articles written by eminent specialists, one, the most important, is that contributed by Prof. THE third of the four volumes of this excellent work has just appeared, and in value and interest this one does not stand behind the two previous volumes.
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