These philosophers, also, notwithstanding they saw above them an infinite number of globes that moved with great rapidity round a common centre, still adhered to their favourite opinions; and never ceased to suppose some whimsical causes for these movements, until the immortal NEWTON clearly demonstrated that it was the effect of the gravitation of these celestial bodies towards each other. Experimental philosophers, however, and amongst them the great Newton himself, have held the cause of gravitation as inexplicable. Notwithstanding the great weight of this authority, it appears manifest that it may be deduced from the motion of matter, by which bodies are diversely determined. Gravitation is nothing more than a mode of moving--a tendency towards a centre: to speak strictly, all motion is relative gravitation; since that which falls relatively to us, rises, with relation to other bodies. From this it follows, that every motion in our microcosm is the effect of gravitation; seeing that there is not in the universe either top or bottom, nor any absolute centre. It should appear, that the weight of bodies depends on their configuration, as well external as internal, which gives them that form of action which is called gravitation. Thus, for instance, a piece of lead, spherically formed, falls quickly and direct: reduce this ball into very thin plates, it will be sustained in the air for a much longer time: apply to it the action of fire, this lead will rise in the atmosphere: here, then, the same metal, variously modified, has very different modes of action. A very simple observation would have sufficed to make the philosophers, antecedent to Newton, feel the inadequateness of the causes they admitted to operate with such powerful effect. They had a sufficiency to convince themselves, in the collision of two bodies, which they could contemplate, and in the known laws of that motion, which these always communicate by reason of their greater or less compactness; from whence they ought to have inferred, that the density of _subtle_ or _ethereal_ matter, being considerably less than that of the planets, it could only communicate to them a very feeble motion, quite insufficient to produce that velocity of action, of which they could not possibly avoid being the witnesses. If Nature had been viewed uninfluenced by prejudice, they must have been long since convinced that matter acts by its own peculiar activity; that it needs no exterior communicative force to set it in motion. They might have perceived that whenever mixed bodies were placed in a situation to act on each other, motion was instantly excited; and that these mixtures acted with a force capable of producing the most surprising results.