Here let me observe by the way, that in considering the velocity of the planets, we are very apt to conceive falsely of it, by taking our ideas from the comparative velo~ city of smaller projected bodies, which bear

no

man imagine that there is no more motion in all the parts of the city, thus on fire together, than there was in the first little spark that began the fire? that there is no more power or force in this prodigious fire, than there was in the scarcedistinguishable spark which began it? But if there be not supposed something mixed in the materials of the city thus on fire, which has a power of moving itself, all the prodi gious force of motion in the city thus on fire must be supposed in the first little spark which began the fire; for nothing can give what it has not. There are innumerable other phænomena which evidently shew, that some parts of matter are self-moving agents, and which ever move, unless hindered by the force of resisting matter." See An Explanation of the first Causes of Action in Matter; printed at New-York, 1745. p. 6.

So reafoned this ingenious author; who, from the phænomena of nature, thought it necessary to attribute action to some matter, and inertness or resistance to other matter. We now express the same thing in clearer terms, and less exceptionable, by shewing which of the elements of matter are passively moved, and which are comparatively active as the established causes of motion to other matter. And to this philosophy must come sooner or later, notwithstanding all the opposition which custom and fashion may raise against those who are the first to propose this doctrine in its native form.

no proportion to their magnitude: and then it appears less credible that they should be moved by any force of the elements. When the mouse runs with all its swiftness, it is outstripped by the foot-pace of the dromedary so the velocity of smaller bodies may be far exceeded by the gentle and equable motion of such bodies as the planets. If we will compare the planet and the cannonbullet, let us have respect to their different magnitudes; and then, what is wonderful in the one, will be easy and natural in the other. If a bullet were taken to represent the earth, and it were placed at a distance from the centre of its orbit proportional to that of the earth, it would seem to move exceedingly slow, if it were to pass over no more than the space of its own diameter in four minutes, and revolve round its axis only once in twenty-four hours. The time of the earth's motion may be accommodated to the bullet with as much propriety as the velocity of the bullet can be accommodated to the earth. If we estimate the motions of the solar system according to their own proper scale, and not according to some diminutive comparison, the motions that obtain in it will be found suitable to the magnitude of the boK 2 dies

dies that are placed in it; and then it will seem reasonable that their motions may be effected by very gentle forces acting insensibly upon them. The medium which produces the great effect of gravity, and occasions such accelerations, begins with a very gentle impulse, which, in the instant when it first takes place, is less than any force we can assign; and yet, by the addition of successive impulses every moment, produces very great effects.

Mediation of Corporeal Causes must be supposed in Nature.

So long as we mean to keep within the limits of philosophy, we must account for the motions of nature by referring them to corporeal causes: and where this cannot be done to satisfaction, we must either give them up, or wait with patience till some better clue of consideration, or some farther light of experience, shall come in to assist us. It is to no purpose to amuse ourselves with names and qualities which contradict the known laws of mechanism, and supersede the operations of the elements. In some cases the causes of motion may be very occult, and

yet

1

yet there may be no necessity for giving them up; for if all space, as later experiments teach us, is filled with active matter, (not active in its own nature, but according to the positive mechanism of the world,) there must be a general stress upon all bodies, which, if it is interrupted in any part, will occasion a motion where its action is freest, and toward that side where there is least resistance. If the internal medium within the pores of dense and solid bodies is in a more. subtile and rarefied state than the external medium, all dense bodies will be attended with an atmosphere of pressure, which will carry light bodies toward them, and confine them to their surface. This principle will bear an application to all the minute instances of fluids in vessels, capillary tubes, fragments of cork floating on water, &c. In the experiments of electricity it has got possession; and as it will be found that electricity only shews us bodies affected in a greater degree, as they are at all times naturally affected in a lesser, (for the whole world is constantly electrified to a certain degree,) the same reasoning which has been adopted in that science, may be extended to all common cases. So that wheresoever we see a

body change its state from rest to motion, we may lay it down as an invariable truth, that this is the effect of matter in motion acting upon matter at rest. That two distant bodies, both supposed at rest, should be able to act upon one another so as to produce motion in each, without the assistance of

any

third substance, is to invest matter with a power of beginning motion in itself; which is the same as to say, that motion is essential to matter, and on this concession the materialist erects his system; so that it is not only a notion false in itself, but extremely dangerous in its consequences: and indeed I have been informed, that a French philosopher has turned to the purposes of atheism, the concession of the moderns in regard to matter and motion. We must either fall into this danger, or, when we see two bodies at rest begin to approach each other, without any visible cause, we must introduce some third body already in motion. And to justify ourselves in this practice, we have nothing to do but to shew that active matter is present, where it is neither seen nor felt: which is now abundantly done by the experiments of electricity, if it had not been sufficiently shewn before on other principles.

There