Professor Pepper adds, "Leslie's principle does apply to clothing, and it appears that if we imitate nature, and, like the Polar bear, wear white, we shall be warmer in winter and cooler in summer".

The power of black to absorb heat was tested by a friend of our own, in his fruit garden. He had the wall behind an apricot tree painted black for one half of the tree, leaving the other side of unpainted bricks. The apricots on the black side were ripe before the others.

Reflection of heat is heat thrown back from polished and bright surfaces; as from a meat-screen; but if the screen be scratched, painted, or dull, it will not reflect or cast back the heat it receives from the fire. Polished boots are cooler than dusty ones from the same cause; a dusty boot absorbs heat.

Polished metals will conduct heat by contact. If a bright steel poker be kept in a hot fire, it will conduct heat; if it were lying in the fender, it would reflect it.

Heat is radiated from one body to another when a non-conducting medium separates them. A fire radiates heat, the burning fuel emitting rays which warm us when near them. Dull and dark substances are radiators: light and polished substances radiate badly; therefore stoves are cleaned with blacklead, which radiates heat better than any other known object.

Bodies which are bad radiators preserve the heat within them. Polished metal is a bad radiator, therefore teapots are made of it, because as it does not radiate well, it keeps the heat of the tea in. Polished metal also keeps cold in it. Hot water will keep hot longest in a metal jug, and cold water (in hot weather) will keep cold longer in one. This fact accounts for the use of tin cans and jugs for bringing hot water to bedrooms. Very brightly polished dish-covers being bad radiators, do not suffer the heat of dishes to escape by radiation, but as polish is essential for non-radiation, the same covers if suffered to become dull, scratched, or dirty, will only badly fulfil the purpose for which they are designed.

Convection of heat, means heat communicated by being carried to another thing, or place. Water is made hot by convection.

Air also (being like water, a bad conductor) is heated by convection.

Water and air both ascend when heated. The water at the bottom of a pot or boiler, and the air nearest to the fire, will both become hot first and then rise. The colder water or air above then descends, but when heated ascends in its turn; thus the whole air in a room, or the whole body of water in a vessel is gradually heated by convection.

The general atmosphere is also heated by convection. The sun (which does not heat the air) heats the earth; the earth heats the air resting on it. This heated air, called "a convective current," rises, and carries heat with it. Colder air takes its place, and is warmed and ascends in its turn.

Fire - our best servant and worst enemy, as the old proverb calls it, is heat and light produced by combustion of inflammable substances, which separate from each other by chemical action, and combine with the oxygen in the air.

Fuel contains carbon, hydrogen and oxygen, with certain mineral substances. Carbon is the solid part of fuel - charcoal is carbon, so are lampblack, coke, and diamonds ! Hydrogen is an inflammable gas; carburetted hydrogen is burned in the lamps in our streets and houses as common gas. It is the lightest substance known; it burns the moment it is ignited, and will, if a light reaches it, explode should there not be enough atmospheric air in the room to render it innocuous. Happily its unpleasant odour is a warning of its presence, which should never be unheeded.

Oxygen is the pure air which gives life. Nitrogen is an invisible gas which will not burn, will not help combustion, and is as deadly as carbonic acid gas. Now three of these elements are employed in making every common fire - i.e., hydrogen gas, carbon, and oxygen; the two former in the fuel, the latter in the air.

The hydrogen is set free by the match, and uniting with the oxygen of the air makes a flame, the flame heats the carbon of the fuel, which also unites with the oxygen and produces carbonic acid gas.

Fire gives forth warmth by liberating latent heat from the air and the fuel. Carbon requires a great deal of heat to make it unite with the oxygen of the air, in consequence of which the fire kindles gradually. A blazing fire burns the fuel quickest, because the inflammable gases then escaping help combustion. A clear, bright fire is more economical, for it burns more slowly, and there is very little smoke with a red hot fire, much less than with one partially black, because the entire surface of the coals being in a state of combustion, very little of the escaping carbon remains uncon-sumed to fly off as soot. Smoke is unconsumed matters separated from the fuel, consisting of minute pieces of carbon, gaseous exhalations, and vapour. It is, we know, possible to consume smoke.

Fresh coals increase smoke, because more carbon and volatile particles are separated from the fuel than can be reduced by combustion, and consequently they fly off in smoke.

The combustion of a fire is very unequal, because the air reaches it in varied currents. The various shades of red, yellow, and white heat, showing the different degrees of combustion, mingled with the unburnt coal, produce the fanciful resemblances we call "faces in the fire".

Coals burn out faster on a frosty day than on a warm one, because the cold condenses the air and thus produces more oxygen; colder air makes the fire burn more intensely.

Our readers are probably well aware that the rays of the sun falling on a fire will often put it out. The reason is, that the solar rays are composed of three parts - lighting, heating, and actinic or chemical rays. The two latter interfere with combustion.

Fires "go out" in summer, not only because less attention is paid to them, but because the hot and rarefied air of summer has its oxygen diffused through a greater space. On damp days, also, fires do not burn well because the air is full of vapour and is too much rarefied. In windy weather, when the air is rapidly changed, plenty of oxygen is supplied, and the fire will burn fiercely. For the same reason, a pair of bellows helps to kindle, or get a fire up, by driving the oxygen rapidly into it.