Aire-pump, the Cylinder being well emptied of Aire, should draw up above an hundred pound weight, moving up as it were of its own accord. For, as the ingenious Experimenter has observed in his third Experiment, this forcible endeavour of the subingression of the Aire is not from the pressure of the ambient Aire as strengthned by the accession of the Aire sucked out, because then he that manages the Pump would find the Resistance of the Aire increased as the Sucker is drawn down lower, which yet is not observed. To which we may adde in reason, that the Aire being nothing but a thin body or Congeries of small particles in perpetual motion, what is pumped out will naturally spread out into such distances as it may move more freely in, that is, into those spaces where the Aire is more thin; so that, as it were in a moment, all the Aire becomes of one and the same consistency. And therefore any new pressure (upon the account of the Aire nearest to the Pump becoming more thick) cannot come into compute in this case.
10. The most plaustble Mechanical Solution therefore that can be given of this Phænomenon is that Hypothesis which the excellent Authour himself has made use of, and which will agree universally to the Aire though in its own natural temper: namely, that there is an Elastick power in the Aire, whether you explain it the Cartesian way, by the playing and whirling of every particle thereof, whereby they attempt to possess a larger space; or whether there be such a compression of the particles as there is in the hairs of a lock of wooll, which will expand it self upon the receding of what bore too strongly against it.
But let this Elastical power consist in this or in what else it will, though the Solution look at first sight very hopefull and promising, yet I must confess (but with submission to better judgments) that the Effect that is attributed to the Hypothesis in this Experiment, seems to me a Demonstration against the Hypothesis it self. For this Elastical power, according to the Experiment, has no less force of pressure then an hundred pound weight or more: which pressure (as in all flexible bodies that have a Spring power in them) is perpetual and every where in the Aire, if it be there at all. And therefore any Cylinder of Aire in the same height from the ground, and of the same diameter with that of the Sucker of the Pump, will press as forcibly as an hundred pound weight.
Now suppose a Lump of Butter in a pair of wooden scales having the same diameter with the Sucker of the Aire-pump: it is manifest that this Butter will be pressed with the force of the pressure of two hundred pound weight, a Cylinder of Aire from beneath and another from above pressing with the force of an hundred pound weight apiece. This would necessarily follow if there were this Elastick power in the Aire. But the Butter is not pressed at all, as appears in that no serose humour is squeezed out of it, nor is it at all flatted or spred out by any such compression, although it have the force of two hundred pound weight pressing it, according to this Hypothesis of the Elastick power of the Aire.
11. Nor can I excogitate any Evasion against this Demonstration, unless it be that the Spring of the Aire pressing against the sides of the Butter as well as the bottom and top, keeps it from flatting. But it is
