Electrical Resistance of Mixtures of Sulphur and Carbon. 347 



"which we may suppose this to happen. It may be that, as 

 Prof. Barrett suggests (Phil. Mag. April 1867), the mischief 

 is due to the irregular flow and consequent ricochetting of the 

 current of gas from side to side of the pipe ; or, again, the 

 cause may lie in the actual production of sonorous disturbance 

 of the kind to which the flame is sensitive, afterwards propa- 

 gated forwards to the burner along the supply-pipe acting as 

 a speaking-tube. The latter explanation was the one that 

 suggested itself to my mind at the time, in consequence of the 

 observation that a hissing sound was easily audible by the ear 

 placed close to the half-open stopcock through which gas was 

 passing : and it was confirmed when I found that a screw 

 pinch-cock could be used for adjustment near the flame with 

 impunity, in which case no sound was perceptible. 



Subsequently further experiments were tried with various 

 nozzles inserted in the supply-tube. These included holes in 

 thin metal plates and drawn-out glass tubes. Even though 

 the rubber tubes were so bent that the streams issuing from 

 the nozzles were directed against the sides, no sound was heard, 

 and no loss of sensitiveness was apparent. It would seem 

 that mere irregularity of flow produced no marked effect, and 

 that, provided no sound attended it, the full pressure could be 

 borne without flaring. 



These observations in no way impair the value of the prac- 

 tical rule laid down by Tyndall. In some cases I have found 

 a flame flare without external excitation when a neighbouring 

 stopcock was partially closed, and in spite of the increase of 

 pressure recover itself when the stopcock was completely 

 opened. When the object is to investigate the conditions of 

 flaring, the use of a manometer near the flame is decidedly to 

 be recommended. 



March 24, 1882. 



XLII. The Effect of Temperature on the Electrical Resistance 

 of Mixtures of Sulphur and Carbon. By Shelford 

 Bidwell, M.A., LL.B.* 



SINCE December 1880 I have from time to time made a 

 number of experiments with the object of ascertaining 

 whether sulphur could, under any circumstances, be made to 

 exhibit the remarkable property possessed by selenium, and 

 in a smaller degree by tellurium, of having its electrical resist- 

 ance diminished by the action of light. 



* Communicated by the Physical Society, having been read at the 

 Meeting on March 25, 1882, 



