4>^ fM Gvbve oT^A^ Jpplicatic^W^ 



applicable to lighting miiies';' their publication "vt'a^ postponed, 

 and I had nearly forgotteii jKeta. ' iiHtJ'F 'rfefhinded by tWe' 

 papers above-mentioned. -''Miu , .ii.. -ji 



'^'l substituted the voltaic ignition 'of si 'platina wire for the 

 disi'uptive discharge. Any one who'ha^ seen the common 

 lecture- table experiment of igniting a platina wire by the vol- 

 taic current nearly to the point of fusion, will have no doubt 

 of the brilliancy of the light emitted ; although inferior to that 

 of the voltaic arc, yet it is too intense for the naked eye to 

 support, and amply sufficient for the miner to work by. My 

 plan was then to ignite a coil of platinum wire as near to the 

 point of fusion as was practicable, in a closed vessel of atmo- 

 spheric air, or other gas, and the following was one of the 

 apparatus which I used for this purpose, and by the light of 

 which I have experimented and read for hours : — A coil of 

 platinum wire is attached to two copper wires, the lower parts 

 of which, or those most distant from the platinum, are well- 

 varnished; these are fixed erect in a glass ol" distilled water, 

 and anotlier cylindrical glass closed at the upper end is in- 

 verted over them, so that its open month rests on the bottom 

 of the former glass ; the projecting ends of the copper wires 

 are connected with a voltaic battery (two or three pairs of the 

 nitric acid combination), and the ignited wire now gives a 

 steady light, which continues without any alteration or incon- 

 venience as long as the battery continues constant, the length 

 of time being of course dependent upon the quantity of the 

 electrolyte in the battery cells. Instead of making the wires 

 pass through water, they may be fixed to metallic caps well- 

 luted to the necks of a glass globe. 



The spirals of the helix should be as nearly approximated 

 as possible, as each aids by its heat that of its neighbour, or 

 rather diminishes the cooling effect of the gaseous atmosphere ; 

 the wire should not be too fine, as it would not then become 

 fully ignited ; nor too large, as it would not offer sufficient re- 

 sistance, and would consume too rapidly the battery consti- 

 tuents ; for the same reason, i. e. increased resistance, it 

 should be as long as the battery is capable of igniting to a full 

 incandescence. 



The helix form offers the aidvantages, that the cooling effect 

 being lessened, a much longer wire can be ignited by the same 

 battery: by this increased length of wire, the battery fuel is 

 oeconomised, while a greater light is afforded ; by the increased 

 heat, the resistance is still further increased, and the con- 

 sumption still further din)inished, so that, contrary to the 

 usual result, the increment of consumption decreases with the 



