VOL. XVI.] PHILOSOPHICAL TRANSACTION'S. 2gT 



it will happen, that at last a body may be reduced to that minuteness, that its 

 gravity pressing downwards, which is in proportion to its bulk, may be less than 

 the resistance of the medium which operates on the surface of the body ; seeing, 

 as was said, the surfaces of bodies do not decrease so fast as their bulks, these 

 decreasing in a triplicate, but those in a duplicate ratio of the diameters of the 

 bodies. 



But because it was said that the forementioned law of hydrostatics is a little 

 defective, I desire to explain myself a little further on that point. In weights 

 falling through the air, were gravity only considered, the proportions of their 

 descents would be exactly as Galileo has demonstrated ; but it is allowed by all, 

 that the resistance of the air not being considered in those demonstrations, they 

 are not mathematically true in practice, but that there is really some deviation 

 from that proportion on account of the air's resistance. Now, what is this less 

 than to say, that the resistance of the air takes off some of the action of gravity, 

 by its opposition. And if so, what shall we say were an iron sphere let 

 through a medium of water ? surely the proportions of its descents would be 

 much more disturbed in it, as water is much more solid and difficult to be sepa- 

 rated or passed through than air, and consequently more of the operation of 

 gravity is taken off or resisted by this opposition of the water than that of the 

 air. And if so, surely there may be a certain degree of gravity, that may be 

 quite taken off by the resistance of the water ; were a pistol bullet let fall 

 through the air it would descend nearly according to the proportions assigned 

 by Galileo ; but were a single grain of sand so let fall, it would be much hindered 

 in its course, and the half of this grain would be still more obstructed ; what 

 shall we then say of the 10,000th part, or of a part the 10,000,000,000th of 

 this, and again of the infinite subdivisions of that, till at last we come to a 

 part that would be wholly resisted or sustained ; such as the minute particles of 

 a body dissolved in a menstruum are ? 



On this account it is, that the above-mentioned principles of hydrostatics is 

 a little defective ; for it does not consider the natural congruity of the parts of 

 a liquor which they unite and keep together ; and therefore liquors have an 

 innate power of resisting a certain degree of force that would separate them ; 

 such as I suppose the degree of gravity in the most minute particles of a body 

 dissolved in a menstruum. 



But I would not be thought wholly to reject my brother's solution of this 

 problem, for that motion in a menstruum which is able to dissolve such a solid 

 body as iron, that is, which can disturb the close and strong cohesion of the 

 parts of iron, may very well be supposed sufficient to sustain those parts in 

 the vessel, wherein the solution was made ; and certainly no better account can 

 possibly be given of such solution than by supposing such an internal motion 



VOL. III. Q a 



