same place. Two French academicians, of the last century, saw at Larochefoucault a man, who, from habit, supported during ten minutes the heat of an oven, in which fruits and meats were cooked; they found the heat to be 112° of Reaumur, 32° above that of boiling water. The rarity of the air, its weak conducting power, and its small capacity for caloric, serve to explain how a person can exist in so warm an atmosphere. It is by its action upon the skin, and the consequences which ensue from that, that fire becomes injurious. Now the "Fire King," who exhibited himself in London last spring, was wrapped up in wide pantaloons, of red wool, a loose mantle also of wool, and wore on his head a great quilted felt cap; and the wool being a bad conductor of heat, this wonderworking genius should awaken the astonishment of the ignorant alone.

Why are porous or spongy substances, as feathers, fleecy matter, &c. bad conductors of heat?

Because, in great measure, of the quantity of air which they have in their structure; air being, probably, the worst conductor known, that is, the substance which, when at rest, impedes the passage of heat the most.-Arnott.

Why does a drop of water roll about on a red-hot iron without evaporation?

Because its surface becomes so highly polished as to reflect all the heat. If the heat be less, the water penetrates the pores of the oxidated iron, and losing its polish is evaporated.

Why is water frozen in a vessel from which the air has been pumped out, and which contains bodies that quickly absorb its vapours?

Because the evaporation of the water is thus accelerated-the heat required for the conversion of one portion of the water into vapour, being taken from the other portion, which is thus reduced to ice.

Why is soft and flabby meat unfit for cooking?

Because, after the rigidity has totally ceased, animal flesh soon experiences the commencement of those chemical changes which terminate in putrefaction.

Why do confectioners melt ice with common salt? Because they thus produce cold much greater than that of the original ice.

Why do not springs freeze?

Because the earth conducts cold or heat but slowly, and the most intense frosts penetrate but a few inches into it; the temperature of the ground, a few feet below its surface, is nearly the same all the world over.Arnott.

Why are many of the gothic halls and cathedrals cool in summer and warm in winter?

Because, in proportion as buildings are massive, they acquire more of those qualities, which have just been noticed, of our mother-earth.-Arnott.

Why is the degree of cold greater the farther we remove from the earth's surface?

Because the air is not heated immediately by the rays of the sun passing through it; but on their meeting with an opaque (or dense) body, as the earth, their heat is elicited, and thence gradually communicated to the surrounding atmosphere.

In winter, the earth, at eighteen inches depth, is warmer than the air; in summer, the air is warmer than the earth at that depth: these effects are owing to the earth being a bad conductor of heat.—Parkes.

Why do the Swiss peasants, when they wish to sow their seed, spread black cloth on the surface of the snow?

Because it may absorb the sun's rays, and facilitate the melting of the snow. Dr. Franklin, to exemplify the effect of the different colours in absorbing heat, covered snow with pieces of cloth of different colours,

at a time when the sun was shining fully upon the snow. Having done so, he observed that the snow under the black cloth was melted first, then that under the blue, then under the brown, whilst that under the white cloth was very inconsiderably melted.

Why are the heights of mountains calculated by the temperature at which water boils upon their summits?

Because, if we diminish atmospheric pressure, we lower the boiling point. Thus, water, under mean atmospheric pressure of 30 inches of mercury, boils in a metallic vessel at 212°. At the top of Mont Blanc, Saussure found that it boiled at 187°, from the atmosphere being less dense there than below.

Why is the air warm in misty or rainy weather?

Because of the liberation of the latent heat from the precipitated vapour.

Why is heated air thinner or lighter than cold air? Because it is a property of heat to expand all bodies; or rather we should say, that we call air hot or cold, according as it naturally is more or less expanded.

Why is a tremulous motion observable over chimneypots, and slated roofs which have been heated by the sun?

Because the warm air rises, and its refracting power being less than that of the colder air, the currents are rendered visible by the distortion of objects viewed through them.

Within doors, a similar example occurs above the foot-lights of the stage of a theatre; the flame of a candle, or the smoke of a lamp.

Why are the gas chandeliers in our theatres placed under a large funnel?

Because the funnel, by passing through the roof into the outer air, operates as a very powerful ventilator, the heat and smoke passing off with a large proportion of the air of the house.

The ventilation of rooms and buildings can only be perfectly effected, by suffering the heated and foul air to pass off through apertures in the ceiling, while fresh air, of any desired temperature, is admitted from below. -Brande.

Why is the atmosphere of theatres, and other crowded places, prejudicial to health?

Because it has been found, that in a theatre, from the commencement to the end of the play, oxygen or vital air is diminished in the proportion of from 21 to 27, or nearly one-fourth, and is in the same proportion less fit for respiration than before.-Lavoisier.

Why are diving-bells restricted in their descent to ten or twelve fathoms?

Because of the density, and more especially the heat, of the air, although renewed by forcing pumps, becoming insupportable.

Why does the bark of trees resemble clothing?

Because it allows the heat to pass from the tree but slowly, and secures, therefore, the temperature necessary to vegetable life.

That caloric is as necessary for the support of vegetable as it is for that of animal life, may be proved by direct experiment. If, in the middle of winter, a hole be bored in a tree, and a thermometer put into it, it will be seen that the tree is many degrees warmer than the atmosphere.

Why does the effect of wind, or motion of the air, quicken evaporation?

Because it removes air saturated with the moisture, and substitutes air which is not, thus producing nearly the case of the substance placed in a vacuum.

Why do liquids evaporate neither so rapidly nor so greatly in air, as in a vacuum?

Because the presence of the air impedes the spreading from the liquid surface of the newly-formed vapour, and keeps it where its pressure resists the forma

tion of more vapour; and, because the air in contact with a liquid, shares its higher temperature with the liquid. Still, in India, flat dishes of water, placed through the night on beds of twigs and straw, kept wet, and in a current of air, soon exhibit thin cakes of ice and thus ice is procured in India, for purposes of luxury.-Arnott.

Why do heated sea-sand and soda form glass ?

Because, by heating the mixture, the cohesion of the particles of each substance to those of its own kind is so diminished, that the mutual attractions of the two substances come into play, melt together, and unite chemically into the beautiful compound called glass. Why is sand used in glass?

Because it serves for stone; it being said, that all white transparent stones which will not burn to lime are fit to make glass.

Why do cracked glass vessels allow liquors to escape more or less?

Because of the various fissures, which are distinguished into four kinds. The first are such, that the Tiquid contained in the broken vessel escapes through them into the air. The second are such as retain the liquid, unless the vessel be immersed in water, or a similar fluid, and then the levels of the two portions of the fluid, tend to approach each other. The third are not permeable, (or, to be passed through) unless the fluids on opposite sides have a chemical action on each other: this is also the effect produced by the membrane of the bladder. The fourth kind are so fine, that no fluid passes, except in a single case.-Fischer. Why is fine table-glass very liable to wear and damage

Because of the great quantity of oxide of lead which it contains, to give it more density and refractive power. Its disadvantages are extreme softness, great fusibility, and liability to be corroded by acids, A