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.
If particles of iron, sulphur, and water be mixed together, these bodies thus capacitated to act on each other, are heated by degrees, and ultimately produce a violent combustion. If flour be wetted with water, and the mixture closed up, it will be found, after some lapse of time, (by the aid of a mic
