VOL. VII.] PHILOSOPHICAL TRANSACTIONS, A*J 



pulsion or percussion from without, which possibly may be the case, and principally 

 from the spring of the air about us; then while this pulsion and percussion is 

 wanting, the bodies accounted heavy will not of themselves begin to fall : which 

 seems to be the present case. 



And this is the more considerable, because we cannot find what is the utmost 

 height at which the quicksilver, thus accumulated, will remain suspended; there 

 having been no height yet attempted, at which, if cleansed, it will not stand ; 

 and that of 75 inches, considering the weightiness of quicksilver, is a very great 

 one, being more than equivalent to 80 feet of water. 



My Lord Brouncker a little alters the case, from what I take to be the hypo- 

 thesis of M. Huygens. For he supposes this purer part of the air to be of like 

 nature with the grosser part, which I think M. Huygens does not; and, though 

 finer than the rest, so as to penetrate glass, which the grosser will not ; yet of a 

 springy nature, as the grosser parts are: which therefore acts, not by its weight 

 only, but by its spring; and therefore when once entered, though in a small 

 proportion, acts as effectually, at its first entrance, as if the whole incumbent 

 air had admission ; its spring being of a like tensure with that of the outward 

 air. But M. Huygens's more subtile matter than air, though he must allow it 

 weight, yet whether he allow it a spring, I cannot tell ; nor does he inform us. 

 And when he says, this more subtile matter without difficulty penetrates glass, 

 water, quicksilver, and all other bodies, which we find impenetrable to air ; I 

 know not whether he mean, without any difficulty, or without great difficulty, 

 though with some. 



But his Lordship, though he allow his springy subtile matter to penetrate 

 glass, yet not without difficulty ; and till it have some room made (as HD) 

 wherein it may recollect itself, cannot exert its spring, and therefore not while 

 top-full of cleansed quicksilver : but, so soon as some room is made for it : 

 whereas if the quicksilver be not purged of air, that little air remaining by its 

 spring begins the motion. He thinks it also not improbable, that a large but low 

 tube of glass, shorter than 29 inches, may stand top-full of quicksilver, though 

 with a small hole in the top, as at K ; at least, if immerged in water, in case air 

 be too subtile for our mechanics. He might also, suitably enough to his own 

 hypothesis, have so explained himself, as to allow his more subtile parts of com- 

 mon air to penetrate quicksilver, but not glass ; and therefore, in case of room 

 for it at HD, it might through the stagnant quicksilver, and that at C, pass 

 upwards to HD, and there exert its spring. 



I shall forbear to dispute against this hypothesis for the present; because I 

 think it more proper to examine by experiment, whether well purged quicksilver 

 may not be made to stand higher than CI, the ordinary standard, suppose at , 



