not intercept an explosion from olefiant gas, would prevent it with fire-damp.
The combustibility of different gases is, to a certain extent, in direct proportion to the masses of heated matter required to inflame them. A red-hot wire, one fortieth of an inch in diameter, will not ignite olefiant gas, but it will inflame hydrogen gas; and the same wire heated white-hot, will inflame olefiant gas, but will not inflame the carburetted hydrogen of the coal-mines, which fortunately is the least combustible of the inflammable gases. The cooling power of metal, in regard to flame, is well shown by encircling a very small flame with a cold iron wire, which instantly causes its extinction. The interruption of the flame, therefore, in the author's safety-lamp, depends upon no recondite cause, but is simply referable to the cooling power of the wire-work tissue.
From the facts contained in the first part of this paper, the author conceives that the light of meteors depends not upon the ignition of inflammable gases, but upon that of solid bodies; that such is their velocity of motion, as to excite sufficient heat for their ignition by the compression even of rare air; and that the phenomena of falling stars may be explained by regarding them as small incombustible bodies moving round the earth in very excentric orbits, and becoming ignited only when they pass with immense rapidity through the upper regions of the atmosphere; while those meteors which throw down stony bodies, are similarly circumstanced, combustible masses.
Having shown, in a former communication, that the temperature of flame is considerably greater than that required for the ignition of solid bodies, the author thought it probable that, during the combination of certain gaseous substances, the heat evolved might be adequate to the incandescence of solid matters exposed to them, though insufficient to render the gases themselves luminous, or, in other words, to produce flame.
In a combustible mixture of coal-gas and air, the author suspended a small wire-gauze safe-lamp, in which some fine platinum wire was fixed above the flame; and when the inflammation had taken place within the cylinder of gauze, the quantity of coal-gas was increased, under the idea that the heat acquired by the mixed gas in passing through the wire gauze would prevent the excess from extinguishing the flame. When this happened, the wire of platinum continued to glow, though there was no inflamed gas in the cylinder; so that the oxygen and coal-gas in contact of the wire seemed to burn without flame, and yet produced heat enough to keep the wire ignited. This conclusion was verified by introducing a hot platinum wire into a
