flame also appears upon brick and tile kilns, which are heated by coal ashes; and in such situations it has been occasionally mistaken for the "ignis fatuus."

The blue flame is supported by the oxygen of the air combining with the excess of carbon, so that carbonic acid is again produced; and this is the reason that a piece of paper cannot be lighted with readiness on the top of a "cinder-fire," the heat may be sufficient to char the paper, but it cannot inflame, because it is enveloped by the carbonic acid, which is slowly rising; if this be quickly dissipated by the breath, or by suddenly opening the door, the paper thus freed is fanned into flame by the contact of the air.

If the piece of paper be held amidst the glowing cinders near the bottom bars of the grate, where the fresh air first arrives it will generally kindle immediately, but will not do so if the cinders are only dull red hot, because such degree of heat, though capable of producing volatile matter from the paper, is incapable of kindling such product; indeed it requires a white heat for its accension; this is obtained either by fanning the fire, or blowing it with the bellows, to excite more rapid chemical affinity between the elements of the fuel and the oxygen of the air.

We frequently hear of thatched buildings, barns, and hay-ricks being accidentally set on fire, from the wadding of a gun incautiously discharged near them, and lodging in the thatch; the wadding may not be hot enough to do this immediately, but by remaining in the thatch or hay for a time, it is fanned by the

wind into flame, and then instantly establishes an extensive conflagration.

"clear

The bright and dark spots presented in a glowing cinder fire," depend upon the intensity of the combustion of some parts of the fuel being greater than others; and these are liable to great variations, by the draught of air proceeding towards the fire; and whilst watching such variations, the imagination soon becomes active in discovering grotesque resemblances between the forms of the fuel and those of familiar objects.

When the fire that has afforded so much information is "burnt out," the ashes in the grate consist of carbon and a small portion of earthy matters; the carbon is capable of burning in a very strong heat, and the ashes are accordingly collected as fuel for tile and brick kilns.

The utility of coal as a source of artificial heat and light needs no comment; the wisdom and beneficence of The Almighty, displayed in the occurrence of extensive strata of coal where forest fuel is scarce, calls forth our admiration and gratitude.

In this country,

66 a land whose stones are iron,"

these ores could not be obtained without the aid of coal, to produce steam as the motive power of the engine, and draw them forth from the mine; neither could they be reduced to the metallic state, without the agency of coal and limestone. We accordingly find that The Creator has associated the ore of iron

or the "iron-stone" with the very agents required for its extraction and reduction.

But the incessant demands that are made upon these subterranean stores of treasure, compel the miner to descend to greater depths, and to encounter greater perils, than were originally needed; and most particularly on account of the air of the mine being rendered inflammable and explosive, by a gaseous exhalation of carbon and hydrogen, similar in composition to the "carburetted hydrogen" of stagnant waters, as mentioned at page 221; this in coal mines is called "The fire-damp," to distinguish it from the natural exhalation of carbonic acid gas, that frequently occurs in limestone and chalk quarries, which is not inflammable, but produces suffocation, and is called "The choak-damp."

"The fire damp" was long unconquerable, and the most terrific explosions, attended with dreadful loss of human life and destruction of machinery, were of extremely frequent occurrence; but The Almighty, who ordained its presence in the mine, permitted the great philosopher-to whose memory a feeble tribute has been paid during this inquiry-permitted him, to reflect, examine, and experiment upon its habitudes and composition, and ultimately to succeed in perfectly effecting its subjection.

From the statement at page 125, it will be evident that flame requires a very high temperature for its existence, or else spontaneous combustion would be

common during the heat of summer: and from the statement at page 71, it will be learned that metals are the best conductors of heat which are known to

man.

These two facts were reasoned upon by the philosopher thus;-as flame requires a high heat for its existence, and as metals are the best conductors of heat, they, when applied to flame, should conduct away its heat, and cause extinction.

The experiment was made with success, and its practical application immediately followed, for safely illuminating a mine contaminated with "Fire-damp;' the flame of a candle being surrounded with metallic gauze, through the apertures of which the "Firedamp" passed, kindled at the flame, burned within the gauze prison, but could not escape from it as flame to explode the surrounding atmosphere, because the good. conducting power of the metal deprived it of heat; and thus was a fiery enemy converted into a fettered slave.

66

The principle of this invaluable invention of the safety lamp," may be experimentally demonstrated by the following simple arrangement; indeed it is the form in which a flame was first protected from kindling the "fire-damp" of a coal mine.

Provide a cylinder of fine wire gauze, such as is used for sieves and window-blinds; let it be about ten inches long, two inches in diameter, and closed at one end with wire-gauze ;—take a lump of soft clay, and mould it around the middle of a candle; light its

wick; then cover it with the wire-gauze cylinder, that the lower edge may be firmly pressed and imbedded in the lump of clay.

Fig. 68.

Unscrew the burner of a gas-lamp, and substitute for it a piece of flexible gas tubing, about two feet long, and half an inch in diameter; make the joint perfect, by tying it round with leather and string, and then bend the tube horizontally; turn on the gas, and allow it to blow from the tube against the part of the wire gauze that is imbedded in the lump of clay, by which the arrangement is held in the hand.

Immediately upon the entrance of the gas,-which is closely analogous in chemical nature to "fire-damp,”it will kindle at the flame of the candle, and by moving the wire-gauze nearer or farther from the pipe, the combustion within will assume various degrees of intensity, but the flame will not escape to kindle the gas that is issuing from the pipe, and which artificially