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The bodies which allow this power free course are called conductors, and those which do not are named non-conductors, Metals are good conductors; feathers, wool, and furs are poor conductors; and water, air, and gases are non-conductors. Another principle of heat is Convection, by which water, air, and gases are warmed.
And one might be pardoned for the enthusiasm which would lead one to suggest that it is only in the supplying of this kind of radiant heat in the modern bath that true and rapid progress can be expected, and possibly that not until this great or partial according as the system of radiation and convection pertains in existing baths revolution has been effected, will the bath, at present used by the few, become the custom of the many.
But, in virtue of a second factor, the difference would be much greater than that consequent on these geometrical relations. The escape of heat from a cooling mass is effected by conduction, or by convection, or by both. In a solid it is wholly by conduction; in a liquid or gas the chief part is played by convection by circulating currents which continually transpose the hotter and cooler parts.
The simplest mode of warming a house and cooking food is by radiated heat from fires; but this is the most wasteful method, as respects time, labor, and expense. The most convenient, economical, and labor-saving mode of employing heat is by convection, as applied in stoves and furnaces. But for want of proper care and scientific knowledge this method has proved very destructive to health.
Each pound of vapor thus liberates, according to Professor Tyndall's estimate, enough heat to melt five pounds of cast iron; so the amount given out where large masses of cloud are forming must enormously add to the convection currents of the air, and hence to the storm-developing power of the forming cyclone.
For our present purpose, it will be sufficient to see how much the whole loss is, without dividing it under the several heads of "imperfect combustion," "radiation," and "convection," by the heated gases passing to the chimney.
The stem being somewhat less than the bore of the tube, a small opening is formed by which the necessary equilibrium of pressure will be established with the external atmosphere. It should be mentioned that the indications of the thermometer during the experiment have been remarkably prompt, the bulb being subjected to the joint influence of radiation and convection.
The heating of the "bath" is the Alpha and Omega of the whole matter. There are two ways in which heat may be applied to the body by direct radiation, as from the sun or an open fire; and by convection, as through a volume of air.
Recently M. Sutherland has imagined that attraction is due to the difference of action in the convection currents produced by the positive and negative corpuscles which constitute the atoms of the stars, and are carried along by the astronomical motions.
Let the bed-clothing be increased, so as to keep warm in bed, and protect the head also, and then the more air comes into a sleeping-room the better for health. In reference to the warming of rooms and houses already built, there is no doubt that stoves are the most economical mode, as they radiate heat and also warm by convection.
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