SAFETY-LAMPS. 201 



lamps of Clanny and Stephenson ; Davy's celebrated lamp 

 was produced in 1815. Let us now consider to what extent 

 it was possible for Davy to have plagiarised the discoveries 

 of either. Humboldt's lamp was impracticable, because the 

 volume of air employed to support combustion was limited. 

 Dr. Clanny's ^was too complicated and cumbrous. A speci- 

 men of Stephenson's lamp has never happened to fall in my 

 way, but I believe it correctly represented as depending for 

 safety by the adoption, as closely as was practicable, of the 

 exclusion system of Humboldt. The latter isolated his burn- 

 ing wick from the external air completely, whence the com- 

 bustion only continued for a limited period. Stephenson, 

 in providing fresh supplies of air, admitted it through one 

 system of concentric rings, and gave exit to the air which 

 had served the purposes of combustion by another system. 



If Davy plagiarised from any one, it was from Stephen- 

 son ; and sure I am that no person who looks at the case fairly 

 will aver even that much. Stephenson, finding that air must 

 be admitted by some channel or other, and again permitted 

 to escape, limited the admission and the escape within the 

 narrowest bounds. In Davy's lamp there is no air-limitation. 

 The burning wick and the external air are free to commune 

 as they please. Davy's aim was not to limit air, but to limit 

 flame. And here I must pause to say a word in explanation 

 of the principle on which Davy's lamp is constructed. 



I suppose an inquirer to be seated in front of a burning 

 wick : it will be a small wick, because that will best illustrate 

 my position. A small wax-taper wick it shall be. The flame 

 is bright and smokeless, because the combustion is perfect; 

 but if now the experimenter plunges a cooling body say a 

 metallic wire into the flame, it burns dull, emits smoke ; 

 in short, its combustive force is diminished. 



If the experimenter bends the extremity of another cool 

 wire into the form of a small ring, he can arrive at a stronger 

 demonstration. Holding that ring within the flame, and 



