could be carried, was early made the subject of philosophic discussion, and, indeed, very easily, though not necessarily, became allied with opposing theological dogmas.

The Peripatetics were the great advocates of the infinite divisibility of matter, whilst the Epicureans, on the other hand, maintained the contrary doctrine that a certain point existed, beyond which the process of division could no longer be carried. Hence, using, as we may with propriety, the language of modern chemistry for the purpose of designating these rival schools -the Epicureans may be said to have believed in an atomic theory and the Peripatetics in a non-atomic theory.

It would be unprofitable to discuss the numerous arguments which were employed by these two schools in support of their opposed doctrines. All of these arguments, save one, were propounded rather as dogmas than as based upon reason; but the excepted one is so essentially rational in its nature, and so specious in its appearance that it merits our consideration.

According to the peripatetic doctrine-a doctrine which amongst the moderns has been sanctioned by the high authority of Descartes-the hypothesis of assuming matter to be composed of atoms, or ultimately indivisible molecules, is absurd on obvious mathemamatical grounds; for it is easy to conceive a particle, however small, capable of subdivision to infinity, a

notion altogether inconsistent with an assumption of the existence of atoms.

This argument is specious; but the possibility of its fallacy is obvious. The idea of continuous subdivision is not referable to a particle as matter, but as filling a position in space, hence the idea of subdivision refers to space and not to matter. This distinction seems to have been apprehended by Zeno, who states in a paradoxical aphorism that, although a body is infinitely divisible, it does not consist of infinite parts. Nor was this distinction left unrecognised by the mathematical mind of Newton, who thus succinctly states his belief in the atomic constitution of the world. "It seems to me," he remarks," that God, in the beginning, formed matter in a solid mass of hard, impenetrable particles; and that these primitive particles, being solids, are incomparably harder than any porous bodies compounded of them; even so very hard as never to wear or break in pieces, no ordinary power being able to divide what God made one in the first creation."

So little profit had accrued from the discussion of these two rival doctrines-so hopeless appeared the chance of arriving at truth by any line of demonstration, or of aiding by any train of plausible evidence even the wanderings of speculation, that philosophers by tacit consent allowed the question to remain at rest, until at length evidence in favour of the Epicurean or atomic theory was derived from a source whence it might have least been expected-from the domains of

chemistry. Anterior to the period of the Saxon chemist Wenzell, in 1777, the opinion had prevailed that chemical combinations were not absolutely fixed and unvarying in composition.* Selecting, for example, the substance chloride of silver, it was consistent with the views of all chemists anterior to the time of Wenzell, to regard this compound not necessarily as being made up of a fixed invariable proportion of chlorine united with the metal silver. The remark is equally true as regards other compounds; therefore, had the exact composition of chloride of silver been known, the idea would never have occurred to chemists of this period to estimate the amount of chlorine existing in a solution, by determining the amount of silver with which it could unite. To Wenzell is attributable the credit of propounding the canon that, " When two neutral salts decompose each other, the results are also neutral," a proposition which conveys within itself the doctrine of definite proportionalism; and is the starting point of a series of deductions, leading us in the end to an acquiesence in the atomic theory.

The nature and tendencies of the discovery made by Wenzell will be best comprehended by limiting our observations to some specific case. Taking, then, the two neutral salts, sulphate of potash and nitrate of baryta, and mixing them in the exact proportions necessary to insure mutual decomposition, we obtain two neutral

* Lehre der Verwandschaft.

compounds as the result. This is shown by the subjoined

In which it is seen that the one proportional of sulphuric acid existing in sulphate of potash is exactly sufficient to neutralize the one proportional of baryta, and the one proportional of nitric acid of nitrate of baryta exactly sufficient to neutralize the one proportional of potash. In other words, in the solution which has served as the medium of decomposition, there does not exist any free sulphuric or nitric acids;-any free baryta or potash. Hence there must have been a mutual proportionality between the reacting compounds in the case under notice, and Wenzell demonstrated by experiment that a similar remark applied to every decomposition of parallel kind.

It is strange that Wenzell did not press to farther limits the curious fact made known by his experiments. Had he gone one step farther, had he weighed the amounts of bodies decomposed, and weighed the results,— had he compared these weights as between two or more cases of decomposition, he could scarcely have failed to reap the honours which were reserved for Dalton twentysix years later.

In order to illustrate the near approach made by Wenzell to a discovery of the laws of definite chemical combination, it will be sufficient to repeat the previous

chart of decomposition, with the addition of the amount by weight of substances decomposed, together with the weighed amount of the results;-and to append a parallel case of decomposition, involving the use of two other salts, also indicating the parts by weight of substances decomposed, and their results.

A comparison between these charts of decomposition will render evident a nexus pervading the numeral equivalents of combination belonging to each substance represented in the diagrams. Thus it will be seen that 88 parts of sulphate of potash would have taken the