“Radiant heat,” said Mr. Wilton, “moves with the same velocity as light, that is, one hundred and ninety-two thousand miles per second. It also follows the same general principles as light in all its motions. It is absorbed, reflected, or transmitted in the same manner as light. And this is true of either luminous heat—that is, heat radiated from a body which is red hot—or obscure, or dark heat.
“As there are good and poor conductors, so there are good and bad radiators of heat. The radiation of heat depends upon three conditions:
“1. Upon the temperature of the body. The higher the temperature, the more rapid and energetic is its radiation.
“2. Upon the surface of the radiating body. A dull, rough surface radiates heat more rapidly than a surface bright and polished.
“3. Upon the substance of the radiating surface. With surfaces equally smooth and bright, some substances radiate heat much better than others. A surface of varnish radiates heat much more powerfully than a surface of gold or silver.
“Ansel, you may, if you can, explain the radiation of heat.”
“I can give no other explanation than that radiation is conduction through that subtle ether which is supposed to pervade all space.”
“Very well; perhaps that is as good an explanation as can be given. But it seems rather like the propagation of an impulse than the spreading of atomic vibrations in every direction. The motion is propagated in straight lines. If it be conduction, it must be carried on by different vibrations from those of ponderable substances. Heat, light, and electricity are supposed to be all propagated through the same theoretical ether. Sir Isaac Newton estimated the density of the ether as seventy thousand times less than the density of our atmosphere, and its elasticity in proportion to its density as four hundred and ninety millions times greater. But the very existence of this universally-diffused ether is a supposition made to account for the phenomena of light, heat, and electricity; and, of course, all its qualities must be theoretical also. Radiation is believed to be the propagation of a motion or impulse through an inconceivably rare and elastic ether.
“Peter, what is the third method by which heat passes from place to place?”
“Convection,” was his reply.