Heat is communicated from one body to another by Conduction, Absorption, Reflection, Radiation, and Convection.

Conduction means the communication of heat from one body to another by contact. Some bodies conduct heat well; others are bad conductors. The best are the metals - lead being inferior to the rest. Light and porous bodies are bad conductors of heat, as hair, fur, wool, eiderdown, cotton, wood, air, water, and snow. Our readers will see in these facts the scientific reason for many of our ordinary practices. Everything which conducts heat from us, must necessarily render us colder; bad conductors on the contrary keep us warm, because they do not rob us of our warmth to transfer it to other objects. Therefore, in winter, when we desire to keep as much heat to ourselves as we can, we dress in woollens and furs, because wool and fur are bad conductors, and will not suffer the warmth of our body to be drawn off by the cold air. Wool and fur do not give out warmth to us from themselves, they simply preserve our own natural heat from escaping into the air, which would otherwise gradually draw it away from us till both it and our body were of the same temperature. For this reason God has clothed his dumb creatures with hair and wool, down and feathers, which, being bad conductors, serve to keep them warm.

Fur, hair, and feathers are bad conductors of heat because the air (which is happily also a very bad conductor) gets amongst their fibres, and thus in a manner defends the creatures covered by them from itself. It may be asked, why, if the air be a bad conductor of heat, it should deprive any part of our bodies exposed to it of warmth, and make us require clothing? The reason is that the air is ever moving and changing; the particles which pass over our skin deprive us of but a small amount of heat at a time, but they move off, and fresh cold ones instantly supply their place, and thus we are continually warming fresh particles of air, to our own loss of temperature.

The act of warming particles of air by conveying to them our own heat, and thus growing colder ourselves, is the reason why a fan or punkah is a relief in warm weather. By agitating the air, we constantly bring fresh cold particles to be warmed by us, and thus bestow on them our superfluous warmth and become ourselves cooler.

We said just now that happily air is a bad conductor of heat. If it were as good a conductor as metal, it would draw the heat from our body so quickly, that we should die of cold. Hot air too would parch and burn us up if it conducted heat as metal does, but fortunately it conveys heat to us as slowly as it takes it away.

The earth is also a bad conductor of heat; the surface may be scorched, but intense heat cannot reach the roots of the trees, neither can cold, in the shape of frost, penetrate more than a few inches beneath the surface. Creative wisdom is shown in this, for if the earth were a good conductor, vegetation would perish; springs of water would be dried up in summer by heat, and in winter frozen hard.

The kettle-holder made of wool, the pieces of ivory which break the metallic communication between the good-conducting silver teapot and it-handle, and the soot - charcoal - covering the bottom of a kettle, which allows the vessel to be taken direct from the fire and held, though full of boiling water, are good and familiar examples of the application of bad conductors.

Snow is a very bad conductor. Its protecting veil consequently defends vegetation from cold and frost, by keeping in the warmth of the earth.

The earth also is a bad conductor; for this reason, the water of a spring is cool in the hottest weather.

The reason that the earth is a bad conductor is that its particles are not continuous. Heat is conducted best by continuity of matter.

Linen is a good conductor of heat; it therefore draws the animal warmth off rapidly, and produces a sensation of chill. Cotton is warmer wear, because it is not so good a conductor as linen. Silk is warm wear also, because it is a bad conductor; raw silk, a very bad conductor, is even a warmer clothing than wool.

The metals are excellent conductors of heat. The iron of stoves conducts the heat of the fire to the air, and thus warms a room. Our readers are, doubtless, aware how hot the handle of a metal teapot will become from the same reason.

The absorption of heat means the sucking in instead of diffusing it. Every good conductor of heat is therefore a bad absorber of it.

The power of absorbing heat depends on the nature of the surface of a body; bright and polished surfaces will not absorb heat as well as black or rough ones do. This is the reason why a kettle, the bottom and back of which are covered with soot, boils much quicker than a bright new one would - for polished metal reflects heat instead of absorbing it; and on this account brilliant tin reflectors, such as plate-warmers, or meat-screens, are used.

"The absorptive power," says Professor Pepper,"was supposed to depend greatly upon the particular colour used. Franklin placed pieces of coloured cloth in the sun's rays on the snow, and found they sank into the snow or melted it in the following order - black, blue, green, purple, red, yellow, white. Tyndall, however, has explained the cause more correctly, and has discovered that the colour has not so much to do with the effect produced as the nature of the material used for the colouring agent. Although it has been stated by Leslie that white surfaces generally reflect heat well, and absorb it indifferently, there is the curious fact, ascertained by Mel-loni, that white lead has quite as great an absorbent power as lampblack; and if the heat comes from boiling water it will absorb twice as much as it would do if it came from an incandescent platinum wire".

Nevertheless colours undoubtedly do affect the heat or coolness of our dress. We think everybody will allow that a black dress in summer is much warmer than a white one, irrespective of its effect on the sight, to which colours appear certainly either warm or cool. Every one is sensible of the heat and glare of scarlet, and of the coolness of green and blue to his eye in the furniture of rooms or in dress.