THOUGHTS o Till: .N Ml |;i: OF TIII(.S.
by which it acquires swiftness, or when amber or a diamond reduced to an extremely tine dust, are divested of colour, that there is any per.-eptil.le. fraction of tin; suhstance of either lost, hut only that their component parts are arranged dim -really as to place. It remains that we try to eradicate from the minds of men an error of which the influence is such, that if credit continues to be attached to it, several of the investigations we have mentioned must be given up in despair as impracticable. For it is the common persuasion, that the ethers (or spirits) of substances, when they have been brought to an extreme degree of exility by heat, evaporate even in the most solid vessels, (such as silver or glass retorts,) through certain impercep tible pores and crevices. This is not true. For neither air, nor such ethers, not even flame itself, volatilize so perfectly, as to become capable of seeking or finding emission through such orifices. But as an exceeding small aperture does not per mit the escape of water, so neither do such pores the passage of air. For, as air is a fluid rarer by far than water, so such pores are proportionally much more minute than visible apertures. Nor would suffocation in a covered vessel he inevita ble, if such exudations either existed, or were competent to produce their supposed effect. And the instance they adduce is pitiful, or rather a fit subject for pity, as are most of the speculations of the common philosophy, when they are brought down to details. They say, that if ignited paper be put in a cup, and the mouth of the cup inverted on a vessel of water, the water is then drawn up wards ; their reason is, that after the flame, and the air subtilized by the flame, occupying as they had done a certain portion of the interior space, had passed out through the pores of the vessel, it remains that some other body should succeed to their place. The same, they say, is the case in cupping glasses, which raise the flesh. And with respect to the water and the flesh succeeding another body which is displaced, their notion is a just one enough, but of the cause which produces that effect, a most ignorant one. For there is no emission, creating vacant space, but only the con traction of that body. For the body into which the flame has passed now occupies much less space than before the flame had been extinguish ed. It is thus that a vacuum is formed, desiderat ing the succession of something else. And this is perfectly clear in the instance of cupping glasses. For when they wish them to act more powerfully on the flesh, they apply to them sponges filled with cold water, that the cold may condense the imprisoned air, and make it gather itself up into smaller space. Thus do we extricate men from the anxiety and the dispiriting impression engendered by the ease with which such finer spirits effect their libera tion; 8) ace the very spirits which they are chiefly ilr, in. ii-, t i iiiilinc, mlnur*, -avnuri, and Uii- like, <io not re. illy i !i.il.- kma their prisons, but are lost within them. Of seeming Quiescence, of Consistency, and of Fluidity VI. That certain bodies appear quiescent and void of motion, is a just impression in reference to their wholes or aggregates, but as respects their parts, it misleads men s opinion. For simple and abso lute immobility, either in the parts or the totality of bodies, there is none; but what is so regarded, is the effect of the obstacles, restraints, and balances with one another, subsisting among motions. For instance, when in the vessels per forated at the bottom, which we use in watering gardens, the water does not find vent through the holes, if the mouth of the vessel be closed, it is evident that this is occasioned by the resilient motion, not the quiescent property of the water. For the water desires to fall, precisely as much as if it were performing the act of descent; but as there is not a body to fill up the vacuity formed at the top of the vessel, the water at the bottom is drawn back, and with considerable force, by the water at the top. Thus, in wrestling, if a man grasp another weaker than himself in such a way that he is unable to move, and yet con tinues to strain his utmost, the motion of renitency is not made less because it is mastered and tied by the stronger motion. Now, the observation we make on false quies cence is useful to be known in numberless cases, and affords no little light in the inquiry into the nature of solid and liquid bodies, or of consistency and fluidity. For solids seem to remain at rest in their positions, but liquids subject to agitation and interfusion of parts. Thus a column, or any other figured body of water, cannot be raised as one of wood or stone. It is, therefore, hastily supposed that the upper parts of the water teml (in their natural motion, as it is termed) to flow downwards, but the corresponding parts of the wood not. But this is not true; since in the parts of the wood forming its top, then the same tendency to motion downwards as in, water; and it would be brought into act, were it not fettered and drawn the other way by a superior motion. Now, the appetite of continuity or horror of separation, which is in itself no less incident to water than to wood, is in the wood stronger than the motion of gravity, in water weaker. For that liquids also partake of this* motion, is manifest. Thus we see in a sin of waterdrops, how. to prevent a solution of con tinuity, the water draws itself out and tapers to | a thin filament, so long as the fluid which sue- ceeds supplies the means; but should water ho wa.iling to maintain the continuity, it then gather*
