additions the matter shall become less and less, until it is not two-thirds of its original volume. If a given bulk of potassium contains 45 atoms, the same bulk of hydrate of potassa contains 70 atoms nearly of the metal potassium, and, besides that, 210 atoms more of oxygen and hydrogen. In dealing with assumptions, I must assume a little more for the sake of making any kind of statement; let me therefore assume that in the hydrate of potassa the atoms are all of one size and nearly touching each other, and that in a cubic inch of that substance there are 2800 elementary atoms of potassium, oxygen, and hydrogen; take 2100 atoms of oxygen and hydrogen, and the 700 atoms of potassium remaining will swell into more than a cubic inch and a half; and if we diminish the number until only those containable in a cubic inch remain, we shall have 430, or thereabout. So a space which can contain 2800 atoms, and among them 700 of potassium itself, is found to be entirely filled by 430 atoms of potassium, as they exist in the ordinary state of that metal. Surely, then, under the suppositions of the atomic theory, the atoms of potassium must be very far apart in the metal, i. e. there must be much more of space than of matter in that body; yet it is an excellent conductor; and so space must be a conductor, but then what becomes of shellac, sulphur, and all the insulators? for space must also, by the theory, exist in them.

Again, the volume which will contain 430 atoms of potassium, and nothing else while in the state of metal, will, when that potassium is converted into nitre, contain very nearly the same number of atoms of potassium, i. e. 416, and also then seven times as many, or 2912 atoms, of nitrogen and oxygen beside. In carbonate of potassa, the space which will contain only the 430 atoms of potassium as metal, being entirely filled by it, will, after the conversion, contain 256 atoms more of potassium, making 686 atoms of that metal, and in addition 2744 atoms of oxygen and carbon.

These and similar considerations might be extended through compounds of sodium and other bodies, with results equally striking, and indeed more so, when the relations of one substance, as oxygen and sulphur, with different bodies are brought into comparison.

I am not ignorant that the mind is most powerfully drawn by the phenomena of crystallization, chemistry, and physics generally to the acknowledgment of centres of force. I feel myself constrained, for the present, hypothetically to admit them, and cannot do without them; but I feel great difficulty in the conception of atoms of matter which in solids, fluids, and vapours are supposed to be more or less apart from each other, with intervening space not occupied by atoms, and perceive great contradictions in the conclusions which flow from such a view.

If we must assume at all, as indeed in a branch of knowledge like the present we can hardly help it, then the safest course appears to be to assume as little as possible; and in that respect the atoms of Boscovich appear to me to have a great advantage over the more usual notion. His atoms, if I understand aright, are mere centres of forces or powers, not particles of matter in which the powers themselves reside. If in the ordinary view of atoms, we call the particle of matter away from the powers a, and the system of powers or forces in and around it m, then in Boscovich's theory a disappears, and is a mere mathematical point, while in the usual notion it is a little, unchangeable, impenetrable piece of matter, and m is an atmosphere of force grouped around it.

In many of the hypothetical uses made of atoms, as in crystallography, chemistry, magnetism, &c., this difference in the assumption makes little or no alteration in the results; but in other cases, as of electric conductors, the nature of light, the manner in which bodies combine to produce compounds, the effect of forces, as heat or electricity, upon matter, the difference will be very great.

Thus, referring back to potassium, in which as a metal the atoms must, as we have seen, be, according to the usual view, very far apart from each other, how can we for a moment imagine that its conducting property belongs to it any otherwise than as a consequence of the properties of the space, or, as I have called it above, the m? So also its other properties in regard to light, or magnetism, or solidity, or hardness, or specific gravity, must belong to it, in consequence of the properties or forces of the m, not those of the a, which, without the forces, is conceived of as having no powers. But then, surely, the m is the matter of the potassium, for where is there the least ground (except in a gratuitous assumption) for imagining a difference in kind between the nature of that space midway between the centres of two contiguous atoms, and any other spot between these centres? A difference in degree or even in the nature of the power consistent with the laws of continuity I can admit, but the difference between a supposed little hard particle and the powers around it, I cannot imagine.

To my mind, therefore, the a or nucleus vanishes, and the substance consist of the powers or m; and indeed what notion can we form of the nucleus independent of its powers? All our perception and knowledge of the atom, and even our fancy, is limited to ideas of its powers; what thought remains on which to hang the imagination of an a independent of the acknowledged forces? As mind just entering on the subject may consider it difficult to think of the powers of matter independent of a separate something to be called the matter, but it is certainly far more difficult, and indeed impossible to think of or imagine that matter independent of the powers. Now, the powers we know and recognise in every phenomena of the creation, the abstract matter in one; why, then, assume the existence of that of which we are ignorant, which we cannot conceive, and for which there is no philosophical necessity?

Before concluding these speculations, I will refer to a few of the important differences between the assumption of atoms consisting merely of centres of force like those of Boscovich, and that other assumption of molecules of something specially material, having powers attached in and around them.

With the latter atoms a mass of matter consists of atoms and intervening space; with the former atoms matter is everywhere present, and there is no intervening space unoccupied by it. In gases the atoms touch each other just as truly as in solids. In this respect the atoms of water touch each other, whether that substance be in the form of ice, water, or steam; no mere intervening space is present. Doubtless, the centres of force vary in their distance one from another, but that which is truly the matter of one atom touches the matter of its neighbours.

Hence matter will be continuous throughout, and in considering we have not to suppose a distinction between its atoms and any intervening space. The powers around the centres give these centres the properties of atoms of matter; and these powers again, when many centres by their conjoint forces are grouped into a mass, give to every part of that mass the proper.

ties of matter. In such a view all the contradiction resulting from the consideration of electric insulation and conduction disappears.

The atoms may be conceived of as highly elastic, instead of being supposed excessively hard and unalterable in form; the mere compression of a bladder of air between the hands can alter their size a little, and the experiments of Cagniard la Tour carry on this change in size until the difference in bulk at one time and another may be made several hundred times. Such is also the case when a solid or a fluid body is converted into vapour. With regard also to the shape of the atoms, and, according to the ordinary assumption, its definite and unalterable character, another view must now be taken of it. An atom by itself might be conceived of as spherical or spheroidal, or where many were touching in all directions, the form might be thought of as a dodecahedron, for any one would be surrounded by and bear against twelve others, on different sides. But if an atom be conceived to be a centre of power, that which is ordinarily referred to under the term shape, would now be referred to the disposition and relative intensity of the forces. The power arranged in and around a centre might be uniform in arrangement and intensity in every direction outward from that centre, and then a section of equal intensity of force through the radii would be a sphere; or the law of decrease of force from the centre outward might vary in different directions, and then the section of equal intensity might be an oblate or oblong spheroid, or have other forms; or the forces might be disposed so as to make the atom polar; or they might circulate around it equatorially or otherwise, after the manner of imagined magnetic atoms. In fact, nothing can be supposed of the disposition of forces in or about a solid nucleus of matter, which cannot be equally conceived with respect to a centre.

In the view of matter now sustained as the lesser assumption, matter and the atoms of matter would be mutually penetrable. As regards the mutual penetrability of matter, one would think that the facts respecting potassium and its compounds, already described, would be enough to prove that point to a mind which accepts a fact for a fact, and is not obstructed in its judgment by preconceived notions. With respect to the mutual penetrability of the atoms, it seems to me to present in many points of view a more beautiful, yet equally probable and philosophic, idea of the constitution of bodies than the other hypotheses, especially in the case of chemical combination. If we suppose an atom of oxygen and an atom of potassium about to combine and produce potash, the hypothesis of solid, unchangeable, impenetrable atoms places these two particles side by side in a position easily, because mechanically, imagined, and not unfrequently represented; but if these two atoms be centres of power, they will mutually penetrate to the very centres, thus forming one atom or molecule, with powers either uniformly around it or arranged as the resultant of the powers of the two constituent atoms; and the manner in which two or many centres of force may in this way combine, and afterward, under the dominion of stronger forces, separate, may in some degree be illustrated by the beautiful case of the conjunction of two sea waves of different velocities into one, their perfect union for a time, and final separation into the constituent waves, considered, I think, at the meeting of the British Association at Liverpool. It does not, of course, follow from this view that the centres shall always coincide; that will depend upon the relative disposition of the powers of each atom.

The view now stated of the constitution of matter would seem to involve necessarily the conclusion that matter fills all space, or, at least, all space to which gravitation extends, (including the sun and its system,) for gravitation is a property of matter dependent on a certain force, and it is this force which constitutes the matter. In that view matter is not merely mutually penetrable, but each atom extends, so to say, throughout the whole of the solar system, yet always retaining its own centre of force. This, at first sight, seems to fall in very harmoniously with Massotti's mathematical investigations and reference of the phenomena of electricity, cohesion, gravitation, &c. to one force in matter, and also again with the old adage "matter cannot act where it is not." But it is no part of my intention to enter into such considerations as these, or what the bearings of this hypothesis would be on the theory of light and the supposed ether. My desire has been rather to bring certain facts from electrical conduction and chemical combination to bear strongly upon our views regarding the nature of atoms and matter, and so to assist in distinguishing in natural philosophy our real knowledge-i. e. the knowledge of facts and laws-from that, which, though it has the form of knowledge, may, from its including so much that is mere assumption, be the very reverse.

It is to be regretted that the memoir of the Rev. Mr. Whewell could not be quoted, being long and obscure. His opinions, it is conceived, have been stated fairly, (1796.)

Motives for republishing my Memoirs on Electrical Theory.

The principal motive, without which the other motives would not have prevailed, is, that having had an interview with the spirit of Franklin expressly to have his advice, it was given decidedly in favour of publication.

There is no door in the temple of science which is so easy of access as that which leads to the department of electricity. The illustrations usually given at a popular lecture may, at the same time, amuse an infant, instruct a student, and yet perplex a profound philosopher. As associated with the phenomena of thunder and lightning, at one time attributed to the bolt of omnipotent Jove, no consequences of scientific research are so awful and sublime: coupled with the magnetic electric telegraph, no other result so miraculous. While vis inertia would keep all nature in statu quo, whether at rest, or like our planet in motion with a velocity fifty times as great as that of a cannon ball: while gravitation tends like the clock weight to produce a definite action and, per se, never to act again : electricity, with a protean diversity of power, appears to be the great instrument of all those changes by which the quiescent influence of the properties above mentioned, is modified in the mundane sphere of chemistry and of life.

Every tyro is aware of the wonderful property imparted to electrics by friction to the tourmaline by heat; and that the same process, on a large scale, will produce sparks, ignition, combustion, deflagration, and destroy animal life by an instantaneous shock. It is notorious that these won

derful powers may all be imparted to a naked pane of glass, while the charge thus imparted is really only two opposite and equal affections, capable of neutralizing each other by due communication. Known also is it, that properties, to a certain extent similar, may be found in a pile of pairs of heterogeneous metals, with the additional power of electrolysis, or, in other words, of resolving chemical compounds into their ingredients, (1376.) It is well known that, by these means, water, long and almost religiously considered as one of the four elements of the universe, can be decomposed into two kinds of air; that the earths and alkalies have been resolved into metals and oxygen; and that there is scarcely any chemical compound consisting of two elements, which may not, when in aqueous solution or in fusion by heat, be directly or indirectly decomposed by electrolysis, as explained in the note to page 384.

These multifarious feats of electricity have caused it to be contemplated as the source of every thing mysterious in nature. It is not surprising, therefore, that those who, through the accessibility of electricity, had become partially acquainted with electrical phenomena, should view it as the source of spiritual manifestations; while those who have a more extensive knowledge of the nature and extent of electrical jurisdiction should perceive at once that the phenomena in question do not fall within its sphere.

After the discovery, by Oersted, of the previously unsuspected reaction between galvanized wire and a magnetic needle, those who had resorted to either one or two fluids to explain electrical phenomena, found themselves completely at fault. Yet the language originated by Franklin has been still employed conventionally. This, though not misleading adepts, introduces confusion in the minds of those who have merely reached the ante-chamber of the electrical department.

Under these circumstances, I deem it expedient to republish the exposition of electrical theory which I first laid before the scientific world in 1848.

I hope that those who endeavour to refer spiritual manifestations or animal magnetism to electricity, in any of its modifications, will study this exposition of my views.

Though, as already stated, there appears to be, for the spirit world, appropriate elements, distinct from those of this mundane world, there is, nevertheless, a correspondence. We mortals can best prepare ourselves to understand the elements of that world by understanding our own. From an idea of our light and our vital air, we may by analogy conceive of theirs as a preliminary to any further knowledge.

The following theory has been submitted to the spirit of Franklin, who fully approved of it, and fully admitted the validity of the reasons assigned by me for substituting this new exposition of electricity for that which goes under his celebrated name.