308 CARBON AND HYDROGEN. 



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 cool- 

 ing 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 con- 

 structed 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 ap- 

 proaches 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. 



The researches which led to the safety-lamp may be 

 regarded as among the most complete examples of 

 correct inductive experiment in the range of English 



