In addition to theology, Newton also studied chemistry; and in 1701 a paper by him, entitled “Scala graduum caloris,” was read at the Royal Society; while the queries at the end of his “Optics” are largely chemical, dealing with such subjects as fire, flame, vapour, heat, and elective attractions.

He regards fire as a body heated so hot as to emit light copiously; and flame as a vapour, fume, or exhalation, heated so hot as to shine.

In explaining the structure of solid bodies, he is of the opinion “that the smallest particles of matter may cohere by the strongest attractions, and compose bigger particles of weaker virtue; and many of these may cohere and compose bigger particles whose virtue is still weaker; and so on for diverse successions, until the progression end in the biggest particles on which the operations in chemistry and the colours of natural bodies depend, and which, by adhering, compose bodies of a sensible magnitude.  If the body is compact, and bends or yields inward to pressure without any sliding of its parts, it is hard and elastic, returning to its figure with a force arising from the mutual attraction of its parts.

“If the parts slide upon one another the body is malleable and soft.  If they slip easily, and are of a fit size to be agitated by heat, and the heat is big enough to keep them in agitation, the body is fluid; and if it be apt to stick to things it is humid; and the drops of every fluid affect a round figure by the mutual attraction of their parts, as the globe of the earth and sea affects a round figure by the mutual attraction of its parts by gravity.”

In a letter to Mr. Boyle (1678-79) Newton explains his views respecting the ether.  He considers that the ether accounts for the refraction of light, the cohesion of two polished pieces of metal in an exhausted receiver, the adhesion of quick-silver to glass tubes, the cohesion of the parts of all bodies, the phenomena of filtration and of capillary attraction, the action of menstrua on bodies, the transmutation of gross compact substances into aerial ones, and gravity.  If a body is either heated or loses its heat when placed in vacuo, he ascribes the conveyance of the heat in both cases “to the vibration of a much subtler medium than air”; and he considers this medium also the medium by which light is refracted and reflected, and by whose vibrations light communicates heat to bodies and is put into fits of easy reflection and transmission.  Light, Newton regards as a peculiar substance composed of heterogeneous particles thrown off with great velocity in all directions from luminous bodies, and he supposes that these particles while passing through the ether excite in it vibrations, or pulses, which accelerate or retard the particles of light, and thus throw them into alternate “fits of easy reflection and transmission.”  He computes the elasticity of the ether to be 490,000,000,000 times greater than air in proportion to its density.