Table 1. Reflecting Power

All metals will conduct heat internally much faster than they can either absorb it at, or emit it from, their surfaces. It will be seen, therefore, that a knowledge of their actual conducting power is not so valuable or essential in the arts of heating and ventilation, as a knowledge of their transmitting power.

11. The law which governs the distribution of heat by conduction is as follows:

All bodies within a given enclosure tend to come to an equal temperature; and the heat within any certain body will tend to diffuse uniformly throughout its whole extent.

If one or more of the bodies have a higher temperature than the others, an interchange of heat will take place, until all are equally heated.

12. The following table shows the relative conducting powers of various materials, silver being taken as the standard:

Table 2

When heat passes from a dense substance to one less dense, or the reverse, the transmission is considerably retarded, and the condition of the surface through which it passes determines the rapidity of the passage.

13. The absorptive and emissive powers of various substances are shown in the following table:

Table 3

Color does not affect the heat-absorbing capacity of the material.

14. Convection

Convection. If there is any difference in the condition of the various layers of a body in weight, electric tension, or chemical condition, they will move about until all the particles have acquired the same condition. The minute motion of each particle is called convection, and the general movement of the mass upon itself is called circulation.