the sense, though assisted with the most finished instruments, nor have their figures and original differences been determined by a just induction. Leaving, therefore, to other philosophers the sublimer disquisition of primary corpuscles or atoms, of which many bodies or worlds have been formed by the fancy, genuine chemistry contents itself with grosser principles, which are evident to the sense, and known to produce effects in the way of corporeal instruments."

As it is clear that matter has various appearances, so if there be only one matter, it must be capable of putting on various forms. This variation of forms has been given as an innate power of matter, and if we extend this idea, we come to the conclusion, more or less clearly expressed by many writers, from the earliest times, that matter itself has no qualities; but that we perceive only the qualities it has put on. Quality means, then, the true matter, or sensible thing which we see. A great many metaphysical, as well as physical difficulties have been removed by allowing a greater number of elements, leaving the difficulties to be solved of a much more profound character.

The remarkable position given to character, making it play the part of matter, is seen well in Hooke's works.*

"I conceive the whole of realities that in any way affect our senses, to be body and motion. By body I conceive nothing else but a reality that has extension every way, positive and immutable; not as to figure, but as to quality; and that the body, as body, is the same, whatever figure it be of: as a quart of water is a quart of water, or a certain quantity of body, though contained in a globe, cylinder, cone, cube, quartpot, or any other figured containing vessel; and as body, it is indifferent to receive any figure whatever; nor has it more extension in the one than in the other vessel, nor can it have

*The Posthumous Works of Robert Hooke, M.D., F.R.S. Folio. 1705. Pages 171-2. He died in 1703.

less; nor is it more essentially a body, when solid, as ice, than when fluid; that is, the minims of it are equally disposed to motion or rest in position to each other; and therefore body, as body, may as well be, or be supposed to be, indefinitely fluid as definitely solid; and, consequently, there is no necessity to suppose atoms, or any determinate part of body perfectly solid, or such whose parts are incapable of changing position one to another; since, as I conceive, the essence of body is only determinate extension, or a power of being unalterable of such a quantity, and not a power of being and continuing of a determinate quantity and a determinate figure, which the anatomists (or atomists) suppose. These, I conceive, the two powers or principles of the world, to wit, body and motion, uniformity of motion making a solid, and difformity of the motion of the parts making a fluid, as I shall prove more at large by and by."

* * * “As for matter, that I conceive in its essence to be immutable, and its essence being expatiation determinate, it cannot be altered in its quantity, either by condensation or rarefaction.; that is, there cannot be more or less of that power or reality, whatever it be, within the same expatiation or content; but every equal expatiation contains, is filled, or is an equal quantity of materia; and the densest or heaviest, or most powerful body in the world contains no more materia than that which we conceive to be the rarest, thinnest, lightest, or least powerful body of all; as gold for instance, and ather, or the substance that fills the cavity of an exhausted vessel, or cavity of the glass of a barometer above the quicksilver. Nay, as I shall afterwards prove, this cavity is more full, or a more dense body of æther, in the common sense or acceptation of the word, than the gold is of gold, bulk for bulk; and that because the one, viz., the mass of æther, is all æther; but the mass of gold, which we conceive, is not all gold, but there is an intermixture, and that vastly more than is commonly supposed, of æther with it; so that

vacuity, as it is commonly thought, or erroneously supposed, is a more dense body than the gold as gold. But if we consider the whole content of the one with that of the other, within the same or equal quantity of expatiation, then are they both equally containing the materia or body."

This argument will not appear so conclusive to his readers, but it serves well to shew how unsettled were the opinions on matter, when a man of Hooke's high standing spoke in this manner. He could not believe in epicurean atoms as he called them, and he had as little faith in "the four elements, the three chemical principles, magnetism, sympathy, fermentation, alkaly, and acid, and divers other chimeras." The quotation is by no means intended as a specimen of Hooke as a philosopher. Aristotle's aether and the abstract ideas of Plato are still perceptible here in confusing the reason and obliterating the observation.

When a definite form is given to the minutest particles of bodies, it leads to their indivisibility by a very easy reasoning, but the moment these ideas become vague, or if a prime matter is allowed, taking various forms, or a few elements changing into each other, essentially the same things, then infinite divisibility is more likely to lay hold of the imagination.

Des Cartes, speaking of the theory of Democritus, says, “it is rejected because he supposed the existence of indivisible corpuscles, because there was a vacuum around each, which could be demonstrated impossible, and because there was weight given to each, whereas no body has it when taken alone, its existence depends on the situation and motion of other bodies."* But he thinks also that natural things might have been made in various ways. We must explain the phenomena as we best can. "Ita non dubium est, quin summus rerum opifex, omnia illa quae videmus, pluribus diversis modis potuerit efficere." He also retained the four elements.

* Renati Des Cartes, Principia Philosophiae. Page 219. Amsterdam, 1677. + Prop. ccii.

S

We find Sennertus, about the same time, expounding Aristotle's opinions on the elements, and looking to the authority of character more than experiment, but he does not give a fifth element such as Aristotle's ether. The argument he gives that there are only four is curious, and another of the interminable varieties of method in which vagueness thinks. "There are two right motions, one from the mean, the other to the mean, there will, therefore, be an equal quantity of simple bodies, subject to these two simple motions, one which absolutely is heavy, called earth; another absolutely is light, called fire. But because nature wishes the world to be one, but contrary extremes cannot constitute one, she always couples the extremes by means (per media), and connects the last of the superior kind with the first of an inferior. This mean is therefore required. But this cannot be one. Because, if so, it would occupy the mean place between the extremes, or between the centre and circumference, and so no right motion (rectus motus) could be given to it. For it could neither be moved to the middle, nor from the middle, nor could it be called more or less heavy. It is necessary, therefore, to have two means, one light, and which may be moved from the middle upward, in respect of which it is heavy, and is called air; the other heavy, and tending to the middle, in respect of which it is light, which is called water. There are, therefore, four elements, fire, air, water, earth. There cannot be a fifth for the same cause, that there cannot be only one But if any one will desire to establish five, his senses and experience disprove it." *

mean.

He endeavours to establish a difference between the pure fire and the common drudge of life, and quotes Scaliger to support him, but in neither of them do we find any distinct ideas of what these differences consist. We are confounded by the great part which hot, cold, moist, and dry, have to play, and it

* Danielis Sennerti Vratislaviensis Epitome Naturalis Scientiae. Oxoniae, 1632. Page 185.

never occurs to them that hot air is air and heat, and that moist air is air and moisture, but they are qualities put on by air at will, or at command, by accident, by growth, by motion, or by life. The qualities of the elements are not substantial forms, but accidents; the original first matter forms the elements which put on various forms, and so perform everything that elements have the power of accomplishing. The changes are performed by generation, fermentation, and corruption.

Baumé, a believer in the four elements and phlogiston, in 1773, says, that it is of no advantage to consult the ancient chemists, they are so ambiguous; and says: *_

"Is it not probable that nature combines the elements in a direct manner by twos and twos, and by threes and threes, by means absolutely unknown to us? If these simple combinations exist, they will be secondary principles, or principles made from principles (principes principiés), of which nature makes use to form compound bodies. Knowledge, on this subject, entirely fails. We have no information on the immediate combinations of the four elements; we only know that they have such a disposition to mix, that it is impossible to have them perfectly pure and isolated from each other."

We have here an opinion freed from the shackles of salt and sulphur, but not beyond the early times, and I think not so penetrating, although as practical as Roger Bacon's.

It will be interesting here to quote Bishop Watson, a man who brought into chemistry more common sense and less pretension than many less penetrating observers. Speaking of elements, he says, "by chemical elements, which are the last products of chemical analysis, we are to understand, not very minute indivisible particles of matter, but the simple homegeneal parts of bodies which are not capable, as far as our experience teaches us, of any farther resolution or division, except in a mechanical sense, into

*

Page 119, Vol. I., of " Chymie Expérimentale et Raisonnée."