DISTRIBUTION OF HEAT.
Heat is distributed by radiation, conduction, and convection. By the first we mean that heated bodies have the power of projecting from themselves, by means of the ether, their own vibrations. Thus the sun is constantly distributing its light and heat in all directions. Conduction takes place where the molecules of a substance nearest a fire first become heated and then impart their motion to the remainder of the mass, somewhat as in a row of suspended ivory balls, the first of which, when struck, transmits its motion from ball to ball, the last one flying off.
Convection takes place in liquids and gases. Here the particles in contact with the heated body becoming lighter by expansion, rise, and are followed by others, thus forming a current.
WATER A POOR CONDUCTOR.
Ex.—Fill a tube nearly full of water, applying a flame to the upper part of the tube. The water at this point will readily boil, while that in the lower part of the tube remains cool, showing that water is a poor conductor, and that liquids must be heated by convection.
The process of warming a room illustrates the three methods of heat distribution. The heat passes through the stove by conduction, away from it by radiation, and to the remote parts of the room by convection.