On Light produced by the Discharge of an Air-gun. 05 



I cOul'd not re-produce the light that evening, I imagined that 

 the first wadding (made of paper,) had been drier and a better 

 electric. 



I now tried dry silk, wbolleh, feathers, paper, rosin, shell-lac, 

 sugar, as well as tubes, and narrow slips of glass. 



The first three and shell-lac occasionally produced light; 

 Sugar arid glass never fail to do so ; but that from the glass 

 was by far most vivid, affording a stream of bright greenish- 

 coloured light, extending about a foot in length from the 

 muzzle. Imagining that it was the velocity with which the 

 electric substance was driven through the air that occasioned 

 the phenomenon, I enclosed small lead shot, peas, &c., in 

 pieces of silk, leaving a tag of silk behind. By this con- 

 trivatice I expected to produce a luminous stream, but I could 

 perceive no light whatever from any of them. 



The preceding experiments were made in the cellar of a 

 half-finished house. I repeated them before sortie friends on 

 the following evening, with the same success. Biit what 

 was our surprise on tt-ying some of the old silk wadding, 

 which had become damp and dirty from lying on the floor 

 since the last night's experiments, to find them yield a much 

 more luminous appearance than before; and, that small 

 pieces of split lath, and even damp saw-dust picked tip off 

 the floor, likewise afforded light. We now tried the gun 

 empty or without a charge in its barrel, when we found it 

 always to give light at the first shot, after the magazine was 

 charged; and this took place whether the charge was high 

 or low. 



My brother remarked that some particles of lime or sand 

 might possibly fall into the barrel, as the gun was rested 

 against the wall, during the time that the magazine was 

 charging ; the attrition of which particles might probably be 

 the cause why the first discharge appeared luminous. Ac- 

 cordingly, on taking precautions against this accident, no light 

 could be obtained. But on introducing a little sand, a beautiful 

 Stream of light was seen at every discharge. 



It was now evident that the light was produced by attrition^ 

 Vol. XV. F 



