13. IN the year 1814 Mr. Buddle, an Englishman, read a paper before a society formed for preventing accidents in coal-mines, illustrating the various modes employed in the ventilation of collieries by plans and sections.

At that time the only light used in coal-mines was

the candle made of sheep or ox tallow, the latter being considered the better.

When the air in the mine became mixed with inflammable gas, the mode of determining its existence and degree of inflammability was described by Mr. Buddle as follows:

"In the first place the candle, called by the colliers 'the low,' is trimmed; that is, the liquid fat is wiped off, the wick snuffed short, and carefully cleansed of red cinders, so that the flame may burn as purely as possible. The candle, being thus prepared, is holden between the fingers and thumb of the one hand; and the palm of the other hand is placed between the eye of the observer and the flame, so that nothing but the spire of the flame can be seen, as it gradually towers over the upper margin of the hand. The observation is generally commenced near the floor of the mine, and the light and hand are gently raised upwards till the true state of the circulating current is ascertained. The first indication of the presence of inflammable air is a slight tinge of blue, a bluish-gray color, shooting up from the top of the spire of the candle, and terminating in a fine extended point. This spire increases in size, and receives a deeper tinge of blue, as it rises, through an increased proportion of inflammable gas, till it reaches the firing-point. The experienced collier

knows all the gradations of shew (as it is called), and seldom fires the inflammable gas, except in cases of sudden discharge."

When the air was highly charged with inflammable gas, the steel mill was resorted to. It consisted of a steel wheel, to which was applied a piece of flint when it was turned rapidly, thus throwing off a continuous succession of sparks, the light of which was rather uncertain however, it was a substitute. But as it required one man to work the mill for every man cutting coal, mining became too expensive; and only those portions of the mine were worked where a sufficient current of air could be brought to bear upon the gas to dilute it sufficiently to allow of candles being used.

In 1814 Dr. Clanny produced a lamp by which a light could be used in an inflammable mixture of gas with impunity. The insulation of the flame was accomplished by means of water; and, although the first lamp which was produced, it was too complicated and cumbrous for general use.

In 1815 at the same time, but in distant localities Mr. George Stephenson and Sir Humphry Davy both produced lamps which insulated lights in inflammable mixtures of fire-damp without exploding the gas externally. These productions have been of the utmost importance in coal-mining, and consequently to the commercial interests of the country generally.

Mr. Stephenson reasoned, that "if a lamp could be made to contain the burnt air above the flame, and to permit the fire-damp to come in below in a small quantity, to be burned as it came in, the burnt air would prevent the passing of the explosion upwards; and the velocity of the current of the air from below would also prevent it passing downwards." He accordingly constructed a lamp of tin, with a hole in the bottom to admit the air to the flame, and a top perforated with holes. By experiments with this lamp he discovered the true principles of the safety-lamp.

Sir H. Davy, at about the same time, communicated with a friend that he had "discovered that explosive mixtures of mine-damp will not pass through small apertures or tubes, and that if a lamp or lantern be made air-tight on the sides, and furnished with apertures to admit the air, it will not communicate flame to the outward atmosphere." He subsequently found that "iron-wire gauze, composed of wires from onefortieth to one-sixtieth of an inch in diameter, and containing twenty-eight wires, or seven hundred and eighty-four apertures to the inch, was safe under all circumstances."

The process by which Mr. Davy arrived at the above conclusion is given by himself in a small work "On the Safety-Lamp for Coal-Mines, with some Researches

on Flame:" "In reasoning upon the various phenomena brought about by my various experiments, it occurred to me, -as considerable heat was required for the inflammation of the fire-damp, and as it produced, in burning, a comparatively small degree of heat, — that the effect of carbonic acid or azote, and of the surfaces of the small tubes in preventing its explosion, depends upon their cooling powers, or their lowering the temperature of the exploding-mixture so much that it was no longer sufficient for its continuous inflammation."

Mr. Stephenson's lamp has been much improved. It consists of a glass cylinder above the lamp, covered by a cylinder of wire gauze; and, instead of air passing through the perforated plate, it passes through the meshes of the gauze (Fig. 1).

The Davy lamp differs from the Stephenson, inasmuch as the former admits air through the meshes of the wire on all sides: consequently, when immersed in an inflammable mixture, the whole cylinder becomes filled with flame, and ultimately the wires become red-hot. Yet they radiate sufficient heat to keep the temperature of the wires below that required for the passage of flame through the meshes, and the lamp continues to burn with safety if kept in a still atmosphere.

Stephenson's lamp, on the contrary, only admits air