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molecular, molecules, bodies, volume, assumptions, conceptions, matter, nature and phenomena

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THEORY Or CORPUSCULAR THEORY). There is much evidence, already, to indicate that the "affinity" that chemical substances have for one another is of an electrical character; and when the physicist has arrived at a more definite knowledge of the ultimate nature of electricity, it is possible (and even probable) that this knowledge will go far to clear up the mysteries of chemical affinity, and to consolidate chemis try and physics into a single science.

The molecular theory in its present form may be said to be a development of the 19th century; for although the celebrated Swiss mathematician, Daniel Bernouilli, had suggested, in the 17th century, that gases consist of little molecules moving freely about among them selves, and that gaseous pressure is due to the collisions of these molecules with the walls of the containing vessels, and although other thinkers had made analogous suggestions which helped to prepare the way for the modern the ory, it was the work of John Dalton, in chem istry, which gave the first great impetus to the molecular theory, by making it, in some form or other, almost a necessity of thought. Dal ton showed (1805) that when substances com bine chemically, they do so in certain definite proportions; and he concluded that the facts of this sort which he amassed could be best explained by assuming that matter consists of exceedingly minute particles, or "atoms," each of which has a definite weight, and that when bodies combine chemically, their atoms come together in pairs, or in threes, or fours, or in other combinations involving only integral num bers, according to the compound formed. (See ATOMIC THEORY). It was shortly afterward observed that when gases combine they do so in accordance with certain simple volumetric laws. One volume of hydrogen, for example, combines with one volume of chlorine, to form two volumes of hydrochloric acid gas; and two volumes of hydrogen combine with one volume of oxygen to form approximately two volumes of steam-gas. To bring facts of this sort into harmony with Dalton's theory, it was suggested by Avogadro in 1811, and independently by Am pere in 1813, that all gases, when under the same conditions of temperature and pressure, contain the same number of molecules per unit of volume. 1Nith these tangible evidences of the molecular structure of matter as an incen tive, physicists and chemists set themselves the task of testing, in all conceivable ways, the con sequences of such a theory; and in the course of a century of experimental and mathematical study, no fact has been discovered which tends to controvert the fundamental doctrine that matter has a molecular structure. The molecu lar theory, in some form, is, therefore, confi dently believed to be true by practically all physicists and chemists. The observations

which have been made, and which must be har monized and explained by the molecular theory, are so numerous and so varied, however, that no single set of mutually consistent hypotheses about the nature of molecules has yet been pro posed, which completely and demonstrably ex plains everything that is known about mat ter.

It is quite probable that our progress in the development of the molecular theory has been seriously handicapped by our natural reluctance throw overboard, when dealing with ultra nucroscopical bodies, conceptions at which we have arnved by studying larger bodies upon which we can experiment, or the behavior of which we can directly observe. Many indica tions of this are already apparent. For exam ple, the principle of relativity (if further study proves it to be sound) will oblige us to substi tute new tnethanical axioms (or postulates) for those of Newton, in many lines of Investiga tion; and we already recognize that when we have to deal with matter moving at extreme velocities (1) we can no longer assume muss to be constant, and (2) we have to distinguish between longitudinal and transverse mass, be cause the behavior of the body with respect to an impressed force is different, according as the force acts parallel to the velocity or at right angles thereto. (See ELECTRON THEORY). In dealing with molecular and sub-molecular bodies and magnitudes, there is no logical rea son why we may not make any assumptions whatsoever that prove to be convenient,— pro sided these assumptions, when the bodies to which they are applied are large and tangible, harmonize with the facts of experience in the world that we can see; and when this fact is fully appreciated, and we have wholly aban doned the attempt to make the behavior of in dividual molecules and corpuscules harmonize with conceptions we have formed from a study of the larger facts of nature, our progress will doubtless be much more rapid. But until we have found out the precise set of assumptions that will hest account for the ultramicroscopic phenomena of the universe, we shall perforce continue to treat the molecule as though it obeyed Newton's laws of motion, except in certain special cases or aspects, where we may know that it does not; and in the transitional stage that science is now entering, we shall be further vexed by having to deal with incompat ible assumptions to a large extent, and to ex plain certain phenomena in accordance with our older conceptions, while at the same time we apply newer and broader conceptions to other closely related phenomena.

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