The Background to Radiation Theory

Abstract

The origins of most scientific theories go back to pre-scientific observations and speculations, not barring radiation theory, the theory of emission and absorption of radiation, of the conversion of light theory and heat into each other. The exchange between heat and light was known since people rubbed sticks or hit flint in order to make fire. Blacksmiths from time immemorial used the color of radiation emitted from hot pieces of metal to judge whether they were hot enough for given purposes. Science picked up when Newton declared fire nothing but radiating air. (Incidentally, he did not know about gases and considered air an elastic fluid; gases entered physics after air was viewed a mixture of oxygen and nitrogen whose components are neither a compound nor separated to layers as fluids should be. Later on the flames were considered not gaseous but plasma, which does not fit the view that matter is solid, fluid or gaseous. But we need not go into that: it should suffice to note that Newton deemed flames hot matter.) Newton illustrated his view with a most beautiful experiment which historians of science regularly overlook; quite apart from its immense importance, it is breathtaking in its simplicity. What Newton wanted to illustrate is that what looks like a flame, what looks like an entity, is nothing but a zone of high temperature. A candle’s flame hardly looks less of a thing than its wick; a camp-fire exhibits its dancing flames as dancing just because they look like things. Imagine a patch of green grass on a sandy bank. Imagine that someone told you there is no grass there; there is a drift of sand into and out of the patch, and that each grain of sand turns green when it enters the zone and sandy-colored again on its way out.