VOL. VII.] PHILOSOPHICAL TRANSACTIONS. 45 



materia subtilis of Descartes or M. Iluygens ; as not necessary to the inquiries 

 in hand. 



To the pressure of this purer matter, which they suppose so eubtile, as to 

 penetrate the mercury, marble, and glass itself, they ascribe the suspension of 

 the quicksilver to so great a height. And my Lord Brouncker in particular 

 had a design of prosecuting the experiment, as M. Huygens now advises, to see 

 if he could bring it to some determination what was the utmost height at 

 which it might be thus made to stand; thereby to determine the pressure of 

 this purer matter, as that of the common air is determined by the Torricellian 

 experiment. But his leisure not then serving, I only gave that brief account of 

 his notion, as it is there inserted: and, whether he has since had leisure, 

 amidst a great press of other business to pursue it, I am not certain. 



Now, though I would not wholly exclude this, if such shall be found to be 

 evinced, yet surely there must be somewhat more in it than that of this subtile 

 matter, to solve the phenomenon, notwithstanding the two experiments now 

 alleged by M. Huygens in favour of it. For, if this matter be so subtile as to 

 press, through the top of the glass, on the quicksilver, and consequently 

 through the upper on the nether of the two marbles, as is acknowledged ; I 

 do not see why it should not balance itself, above and below, in the same man- 

 ner as common air would do, if the tube were pervious to it at both ends, and 

 the quicksilver, by the preponderance of its own weight, fall presently. 



And the answer, that, though the glass be- penetrated by it, yet not in so 

 copious a manner as where no glass is; does not to me solve the difficulty: be- 

 cause the same obstacle remains just in the same manner when the tube is in 

 part emptied, and when the quicksilver is unpurged : the pores of the glass not 

 being, by either of those, made more open or more pervious. And if we sup- 

 pose the subtile matter by percolation to be strained through, with some dif- 

 ficulty, as air or water would be through a cloth, this might possibly cause the 

 quicksilver, when it does sink, to sink gradually; but not, as we see it, suddenly 

 to fall to the height of 29 inches; as from D to I. 



The connection or cohesion of the parts of quicksilver, either to each other, 

 or to the sides of the glass, which Mr. Huygens supposes to require, for their 

 separation, a greater force than is in these percolated particles, till they have 

 room made for them to combine; seems to me the less coiisiderable, because it 

 is not so necessary to separate them from each other, since they may un- 

 separated slide down by the sides of the glass ; to which, it is well known, and 

 visible to the eye, the quicksilver is not at all apt to stick, but doth rather de- 

 cline that contact; in like manner as we find water not apt to join with oil or 

 grease; though water to glass, and quicksilver to gold, do very readily apply 



