218 Newton's Letters, Hypothesis and Experiments 



of receding from one another. But, on the other hand, to 

 counterpoise this endeavour, there will not yet be any excess 

 of density of the aether which surrounds the bodies, above 

 that of the aether which is between them at the line I K. But 

 if the bodies come nearer together, so as to make the aether 

 in the mid-way line I K grow rarer than the surrounding 

 aether, there will arise from the excess of density of the sur- 

 rounding aether a compressure of the bodies towards one an- 

 other, which when by the nearer approach of the bodies it 

 becomes so great as to overcome the aforesaid endeavour the 

 bodies have to recede from one another, they will then go to- 

 wards one another and adhere together. And, on the con- 

 trary, if any power force them asunder to that distance, where 

 the endeavour to recede begins to overcome the endeavour to 

 accede, they will again leap from one another. Now hence 

 I conceive it is chiefly that a fly walks on water without wet- 

 ting her feet, and consequently without touching the water; 

 that two polished pieces of glass are not without pressure 

 brought to contact, no, not though the one be plain, the other 

 a little convex; that the particles of dust cannot by pressing 

 be made to cohere, as they would do, if they did but fully 

 touch ; that the particles of tinging substances and salts dis- 

 solved in water do not of their own accord concrete and fall 

 to the bottom, but diffuse themselves all over the liquor, and 

 expand still more if you add more liquor to them. Also, that 

 the particles of vapours, exhalations, and air do stand at a di- 

 stance from one another, and endeavour to recede as far from 

 one another as the pressure of the incumbent atmosphere will 

 let them ; for I conceive the confused mass of vapours, air, 

 and exhalations which we call the atmosphere, to be nothing 

 else but the particles of all sorts of bodies, of which the earth 

 consists, separated from one another, and kept at a distance, 

 by the said principle. 



From these principles the actions of menstruums upon 

 bodies may be thus explained: suppose any tinging body, as 

 cochineal or logwood, be put into water; so soon as the water 

 sinks into its pores and wets on all sides any particle which 

 adheres to the body only by the principle in the second sup- 

 position, it takes off, or at least much diminishes, the efficacy 

 of that principle to hold the particle to the body, because it 

 makes the aether on all sides the particle to be of a more uni- 

 form density than before. And then the particle being 

 shaken off by any little motion, floats in the water, and with 

 many such others makes a tincture ; which tincture will be of 

 some lively colour, if the particles be of all the same size and 

 density ; otherwise of a dirty one, for the colours of all natural 



