EXPERIMENTS OF POUILLET. 315 



external surface, positive electricity was indi- 

 cated, as in the experiments of Mr. Read, which 

 became more and more intense as the distance 

 diminished, until the coil touched the flame, 

 when nearly all signs of electricity disappeared. 

 Hence it was concluded, that around the flame 

 of hydrogen gas, there is a sort of atmosphere 

 at least 4 inches in thickness, which is always 

 charged with positive electricity. 



Now, it is obvious that aqueous vapour is pro- 

 duced during the combustion of hydrogen gas, 

 constituting an atmosphere above and around the 

 flame ; which vapour gives out positive electricity 

 as proved by Mr. Read. It is also evident, that 

 in the immediate vicinity of the flame, the va- 

 pour cannot be condensed by the platinum coil ; 

 and therefore cannot give out much, if any, 

 electricity. It is for the same reason, that the 

 vapour of the atmosphere gives out but little 

 electricity during the heat of a clear day, which 

 increases in the evening. When Pouillet placed 

 a small coil of platinum wire in the centre of the 

 flame, so that it was enveloped on all sides, and 

 made to communicate with a condenser, the 

 instrument was electrified negatively. This is 

 a thermo-electric phenomenon which has very 

 little connexion with atmospheric electricity, as 

 will be seen hereafter. He found that during 

 the combustion of alcohol, aether, wax, oils, fat, 

 and many vegetable bodies, the same phenomena 



