FROM these we have selected the following, as giving, unitedly, a pretty fair reply to the several questions. Some of our correspondents are altogether wrong; but it would gain no good end, and take up too much room in our columns, to specify and meet all their errors. We must do this by simply pressing on each and all, whose replies are not printed, a thoughtful perusal of the subjoined answers. Wherever their answers differ in principle from these they are incorrect, and they may thus rectify their own mistakes. We are highly gratified with the ready and general response that has been given to our questions; and we beg our correspondents, whose papers have not been deemed fit for publication, or superseded by those we give, not to be discouraged, but to try again.

ANSWERS TO QUERIES IN THE

FEBRUARY NUMBER. FIRST QUERY FROM "S. F.," AND

THIRD FROM "HENRY."

ANSWER BY G. W. "The reason that the marble hearth or the penny feels colder than the carpet or the cork may be found in the fact that dense bodies are in general the best conductors of heat;

light, porous bodies, the worst. Hence, when the foot or hand comes in contact with so dense a body as marble or copper, the heat is so rapidly conveyed from it as to give rise to the feeling of coldness; but when in contact with so porous a substance as the carpet or a cork, it passes so slowly as to continue the sensation of warmth."

ANSWER BY F.

"To explain this phenomenon we must remember that the names 'heat' and 'cold' are relative terms used to designate the process of assimilation which takes place when bodies of different temperature come in contact with each other. Some substances are quicker at imbibing or imparting heat than others, and are called accordingly good or bad conductors. Metals and marbles are good conductors, though not equally so, and imbibe a considerable portion of heat. Hence it is, that when in cold weather we touch the hearth or the penny, a considerably larger quantity of heat is by them absorbed from us than would be by a woollen carpet or a piece of cork, which are bad conductors. In the former case, we

were sensible of losing heat, and describing this sensation, by the common mode of expression, we say, "It feels cold."

The same principle regulates our clothing in winter, when our garments are made of wool, fur, velvet, &c.; all these being bad conductors of heat, and preserving thus the animal warmth about the body."

ADDITIONAL ILLUSTRATIONS. Metals are the best conductors of heat; liquids next, and gases next. Amongst solids, gold, silver, and cop

per are the best; glass, bricks, and many stony substances are bad; but fur, hair, charcoal, and porous or spongy substances, the worst.

Examine an ice-house. It is sur

rounded by bad conductors, to prevent the admission of heat. Notice the handles of the teapot, the blacksmith's tools, the Italian irons of the laundry-maid, the soldering-iron of the tin-smith. They are all made of wood, or other bad conductors, to prevent the heat proceeding to the hand. Look at the large furnaces used for smelting metals, or in the manufacture of glass, or china, where great internal heat is needed. They are all surrounded by bad conductors. But look at the stoves placed in the middle of your rooms; they are surrounded with iron and other good conductors, to give out the heat.

Put the poker in the fire till it is red hot, taking care to place the handle higher than the other end. The heat is speedily conducted along, so that you cannot bear to touch it.

Put a piece of dry wood of the same length and size into the fire.

The upper end remains cool a long time.

Get the Italian iron of the laundry-maid, and make it red hot. You cannot bear to touch the iron part that enters the wooden handle, yet you can hold that handle comfortably, and scarcely perceive that its temperature is changed.

SECOND QUERY FROM S. F.
ANSWERED BY G. W.

"The cause of the water bottle cracking when the water which it contains freezes, is ascribed to the peculiar position of its particles at the time of congelation. Ice is, in fact, crystallized water, and while forming the particles arrange themselves in different positions crossing each other, at angles of 60° and 120°, and consequently taking up more room than when liquid. In proof of this you may observe the surface of water while freezing in a saucer."

ANSWER BY F.

"Heat generally expands bodies, and cold contracts them: but in the case of freezing nature has deviated from her general rule, and water when frozen takes up more room than before. This is caused by the arrangement of its crystals, which do not form a compact body, but have small interstices between them, increasing considerably its bulk.

So potential is its force when thus frozen that mighty rocks have been splintered by the simple freezing of the water gathered in their crevices."

ADDITIONAL ILLUSTRATIONS.

Take a saucer or small basin, around the inner surface of which a

line is distinctly marked at about half an inch or more from the edge, and fill it with water to that line. Put it in the open air some frosty night, and in the morning, when it is frozen over, observe how much it has risen above that line; increased in bulk.

Fill a phial with water, and cork it tightly. Put it out some frosty night, and in the morning, if the water be frozen, the phial will be burst.

Throw a piece of ice upon a basin of water. It floats, showing that ice is lighter than water, bulk for bulk.

FIRST QUERY FROM HENRY."

ANSWERED BY G. W.

"When you apply heat to the bottom of a vessel containing any liquid the lower portion of the liquid becomes warmer and lighter, and therefore rises to the top. Another portion is then heated, which also rises; and so on until the heat is propagated throughout the whole. On the contrary, when you heat the surface of the liquid, the cooler parts cannot rise to displace the warmer, on account of their greater weight. So that the heat can be conveyed downwards only by slow transmission from particle to particle."

ANSWER BY S. S.

"Heat is the repulsive property of matter in opposition to gravitation, which has the tendency to draw substances together. It is communicated in two ways:

1st. By conduction, when it passes from one body to another placed in contact with it; and

2nd. By radiation, when it proceeds in rays, as from the sun or the fire.

Metals are good conductors of heat; liquids are not so, they conduct it but slowly.

When a vessel containing liquid is placed over a fire, the heat is conducted through the metal to the lower portion of the liquid. Thus heated it is immediately expanded, and made lighter than the surrounding fluid, causing it to rise to the top, displacing the colder and heavier portions there, and making them descend, till in turn the whole mass is heated.

When heat is applied to the surface the same result cannot follow. The heat passes, of course, by conduction to the liquid immediately below and in contact with it, but as this is rendered lighter and less dense than before, it cannot sink, and the heat must be diffused through the whole mass, on the principle of conduction from particle to particle, which, as the liquid is a bad conductor, would be very slowly done."

ADDITIONAL ILLUSTRATIONS.

Take a glass tube of, say, six inches long, and sealed at one end. Quarter fill it with some coloured water, and then carefully fill up to near the top with clear water, but so as not to mix the two. Apply a spirit lamp to the upper part of the tube till the clear water at the surface boils. You will see that all below is still left undisturbed.

Now apply the lamp to the sealed end of the tube, and the coloured water will be seen to rise in small