Every equivalent of carbon and of hydrogen in the burning body unites with two equivalents of oxygen, in strict conformity with the laws of combination. The flame of hydrogen, if pure, gives scarcely any light, but combined with the solid particles of carbon, it increases in brightness. The most brilliant of the illuminating gases is the olefiant gas, produced by the decomposition of alcohol, and it is only hydrogen charged with carbon to the point of saturation. Flame is a cone of heated vapour, becoming incandescent at the points of contact with the air; a mere superficial film only being luminous. It is evident that all the particles of the gas are in a state of very active repulsion over the surface, since flame will not pass through wire gauze of moderate fineness. Upon this discovery is founded the inimitable safety-lamp of Davy, by means of which the explosive gases of a mine are harmlessly ignited within a cage of wire gauze. This effect has been attributed to a cooling influence of the metal; but, since the wires may be brought to a degree of heat but little below redness without igniting the fire-damp, this does not appear to be the cause. The conditions of the safety lamp may be regarded as presenting examples exactly the converse of those already stated with reference to the spheroidal state of water; and it affords additional evidence that the condition of bodies at high temperatures is subject to important physical changes. The principle upon which the safety lamp is constructed is, that a mixture of the fire-damp and atmospheric air in certain proportions explodes upon coming in contact with a flame. This mixture passes readily through a wire gauze, under all circumstances, and it, of course, thus approaches the flame of the lamp enclosed within such a material, and it explodes. But, notwithstanding the mechanical force with which the exploding gas is thrown back against the bars of its cage, it cannot pass them. Consequently, the element of destruction is caught and caged; and notwithstanding its fierceness and energy, it cannot impart to the explosive atmosphere without, any of its force. No combustion can be communicated through the wire gauze.