"This mythological tradition has, however, one falsehood: there was no need that men should steal fire from the gods; God freely gave it. Heat is indeed a gift from heaven." CHAPTER V. CONVEYANCE AND VARIETIES OF HEAT. "To-day we review the modes in which heat passes or is conveyed from place to place. It is evident that if heat were confined to the very place or point where it is generated, it could subserve none of those uses to which it is now applied in the economy of Nature or in the works and arts of man. But heat passes from place to place with great facility, and by one method, with the speed of light, it tends to diffuse itself evenly through all; it seeks an equilibrium. The modes of its diffusion, or conveyance, are three in number. Ansel may name them." "Heat passes from place to place and from body to body by 'conduction,' by 'radiation,' and by 'convection.'" "What is meant, Ansel, by the 'conduction' of heat?" "The passing of heat from atom to atom and from particle to particle through a body is called conduction." "That is right. I will call upon Peter to give some illustrations of the conduction of heat." "The examples are so many," Peter answered, "that I hardly know what to mention first. If I hold a pin in the flame of a lamp, the part of the pin that touches the flame is first heated, but soon the heat runs along the whole length of the pin and burns my fingers. The parts of a stove which touch the fire are first heated, and from them the heat spreads through the whole stove. A pine-wood shaving, kindled at one end, is heated by conduction, but the heat passes through it very little faster than the flame follows. Heat escapes from our bodies by being slowly conducted through our clothing. There is no end to the examples of conduction which one might give." "We must not think of the conduction of heat," said Mr. Wilton, "as if it were a fluid slowly absorbed by a porous body, as water poured upon the ground soaks into it, or as water percolates through a lump of sugar and moistens the whole of it. We must remember that the transfer of heat is not a transfer of any substance, but a transfer of motion. One atom is set in motion, and strikes against another atom and sets that in motion, and thus motion is communicated from atom to atom and from molecule to molecule through the whole mass of matter till every atom is agitated with the heat vibrations. Do all bodies conduct heat with equal rapidity?" "No, sir," replied Ansel; "there is the greatest possible difference. Some substances are called good conductors, because heat permeates them so readily and rapidly; others conduct heat very slowly, and are called poor conductors or bad conductors."