Ever since the period when Newton established the great law of gravity, philosophers have occasionally speculated on the existence of some more comprehensive law, of which gravity itself is a consequence. Although some have considered it vain to search for a more general law, the great philosopher himself left encouragement to future inquirers; and the time, perhaps, has even now arrived, when such a discovery may be near its maturity. It would occupy too much space to introduce many illustrations of this opinion; there is, however, one which deserves attention, because it is not merely a happy conjecture, but the hypothesis on which it rests has been carried out by its author, through the aid of profound mathematical reasoning, to many of its remote consequences. [179/180]
M. Mosotti1 has shown, that by supposing matter to consist of two sorts of particles, each of which repels similar particles, directly as the mass, and inversely as the squares of their distances, whilst each attracts those of the other kind, also according to the same law,— then the resulting attractions explain all the phenomena of electricity, while there remains a residual force, acting at all sensible distances,, according to the law of gravity.
Many of the discoveries of the present day point towards some more general law; and many philosophers of the present time anticipate its near approach. Under these circumstances, it may be interesting as well as useful briefly to state the principles which such a law must comprehend; and to indicate, however imperfectly, the path to be pursued in the research.
If matter be supposed to consist of two sorts of particles, or rather, perhaps, of two sorts of centres of force, of different orders of density; and if the particles of each order repel their own particles, according to a given law, but attract particles of the other kind, according to another law, — then, if we conceive only one particle of the denser kind to exist, and an infinite [180/181] number of the other kind, that single particle will become the centre of a system, surrounded by all the others, which will form around it an atmosphere denser near the central body.
If we conceive a stream of particles, similar to those forming the atmosphere, to impinge upon it, so as just to overcome its resistance, they will, whilst continually producing undulations throughout its whole extent, gradually increase its magnitude, until it attains such a size, that the repulsion of the particles at the outer surface of this enlarged atmosphere is just balanced by the attraction of the central particle. If the stream continue after this point is reached, the whole outer layer will be pressed a little beyond the limit of attraction, and will fly off at right angles to the surface, which might then be said to radiate.
If the whole of the space in which such a central particle with its atmosphere is placed, is itself full of atmospheric particles, then their density will increase in approaching the central body; and if a stream of such particles were directed towards the centre, they might produce throughout the atmosphere vibrations, which would be transmitted from it in all directions.
If two such central particles, with their atmospheres, exist at a distance from each other, they will be drawn together by a force depending on the difference between [181/182] the mutual repulsion of their atmospheres and central bodies respectively for each other, and the attraction of each central particle for its neighbour's atmosphere: and in order to coincide with the existing law of nature, this force must be directly as the mass, and inversely as the square, of the distance. The other conditions which such a law must satisfy, are —
1. That the juxtaposition of such atoms must, in some circumstances, form a solid body: —
2. In other circumstances, a fluid.
3. That again, in still other circumstances, its particles shall repel each other, or the body become gaseous.
4. In the first state the body must possess cohesion, tenacity, malleability, elasticity; the measure and extent of each of which must result generally from the original law, and in each particular case from the constants belonging to the substance itself.
5. In the second state, it must possess capillarity, susceptibility of being compressed without becoming solid, as also elasticity.
But besides these, the central atoms must admit of a more intimate approach, so that their atmospheres may [182/183] unite and form one atmosphere. This might constitute chemical union. Binary compounds might then (supposing the distance between the two central particles to be very small, compared with the diameters of the atmospheres) have atmospheres not quite spherical, and attracting differently in different directions; thus possessing polarity. Combinations of three or more atoms, as the central body of one atmosphere, might give great varieties of attractive forces. Each different combination would give a different atmosphere; and the equation of its surface might, perhaps, become the mathematical expression of the substance it constituted. Thus, all the phenomena produced by bodies, acting chemically on each other, might be deduced from the comparison of the characteristic surfaces of the atmospheres of their atoms. Another result, also, might ensue. Two or more central atoms uniting, might either not be able to retain the same amount of atmosphere, or they might possibly be able to retain a larger quantity. If the particles of such atmospheres constituted heat, it would in the former case be given out, and in the latter absorbed by chemical union.
Hence the whole of chemistry, and with it crystallography, would become a branch of mathematical analysis, which, like astronomy, taking its constants from observation, would enable us to predict the character of any new compound, and possibly indicate the source from which its formation might be anticipated. [183/184]
For the sake of simplicity, two species of particles only have been mentioned above; but it seems more probable, that matter consists of at least three kinds.
Suppose each of the three kinds to repel its own particles; and the central atom, whilst it repels similar particles, to attract those of the two other kinds; and moreover, that the latter are either repulsive, or indifferent to each other. We might then conceive matter to be made up of particles, each having a central point, with an atmosphere surrounding it, and this atmosphere again inclosed within another and larger one.
Under such circumstances, the outer atmosphere might give rise to heat and light, to solidity and fluidity, and the gaseous condition; to capillarity, to elasticity, tenacity, and malleability. The more intimate union of the central atoms, by which two or more become enclosed in one common atmosphere of the second kind, might represent chemical combinations, and perhaps that atmosphere itself be electricity. Possibly, also, this intermediate atmosphere, acted on by the pressure of the external one, and by the attraction of the central atom, might take the liquid form. These binary or multiple-combinations of the original atoms, and their smaller atmospheres, would still be enclosed in an atmosphere of the outer kind, which might be nearly spherical. The joint action of the three might, at sensible distances, produce gravity. [184/185]
The reader should, however, bear in mind, that these hints are thrown out only as objects of reflection and inquiry; and that nothing but a profound mathematical investigation can establish them, or even give to them that temporary value which arises from any hypothesis, representing a large collection of facts. [185/186]