ETHER AND GRAVITY

From a letter to Robert Boyle¹

Honored Sir,

I have so long deferred to send you my thoughts about the physical qualities we speak of that, did I not esteem myself obliged by promise, I think I should be shamed to send them at all. The truth is, my notions about things of this kind are so indigested that I not well satisfied myself in them; and what I am not satisfied in I can scarce esteem fit to be communicated to others, especially in natural philosophy, where there is no end of fancying. But because I am indebted to you, and yesterday met with a friend, Mr. Maulyverer, who told me he was going to London and intended to give you the trouble of a visit, I could not forbear to take the opportunity of conveying this to you by him.

It being only an explanation of qualities which you desire of me, I shall set down my apprehensions in the form of suppositions as follows. And first, I suppose that there is diffused through all places an etherial substance, capable of contraction and dilatation, strongly elastic, and, in a word, much like air in all respects, but far more subtle.

2. I suppose this ether pervades all gross bodies, but yet so as to stand rarer in their pores, than in free spaces, and so much the rarer as their pores are less; and this I suppose (with others) to be the cause why light incident on those bodies is refracted toward the perpendicular, why two well-polished metals cohere in a receiver exhausted of air, why [mercury] stands sometimes up to the top of a glass pipe though much higher than thirty inches, and one of the main caused why the parts of all bodies cohere; also the cause of filtration and of the rising of water in small glass pipes above the surface of the stagnating water they are dipped into; for I suspect the ether may stand rarer, not only in the insensible pores of bodies, but even in the very sensible cavities of those pipes; and the same principle may cause menstruums to pervade with violence the pores of the bodies they dissolve, the surrounding ether, as well as the atmosphere, pressing them together.
3. I suppose the rarer ether within bodies and the denser without them not to be terminated in a mathematical superficies, but to grow gradually into one another; the external ether beginning to grow rarer and the internal to grow denser at some little distance from the superficies of the body, and running through all intermediate degrees of density in the intermediate spaces; and this may be the cause why light, in Grimaldo's experiment, passing by the edge of a knife or other opaque body is turned aside and as it were refracted, and by that refraction makes several colors ...
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