Because it takes up some portion of the heat, but it does not alter the direction of the rays.
This is clearly illustrated by reference to rays of light which are seen under many circumstances. But they are never bent, moved, nor in any way affected by the wind.
190. Why will not a current of air disturb the rays of heat, just as it would a spider's web, or threads of silk?
Because heat is an imponderable agent, that is, something which cannot be acted upon by the ordinary physical agencies. It has no weight, presents no substantial body, and is, in these latter respects, similar to light and electricity.
191. What other sources of radiation of heat are there besides the sun and the fire?
The earth, and all minor bodies, are, in some degree, radiators of heat.
192. What substances are the best radiators?
All rough and dark coloured substances and surfaces are the best radiators of heat.
193. What substances are the worst radiators of heat?
All smooth, bright, and light coloured surfaces are bad radiators of heat.