1841] WRITINGS OF JOSEPH HENRY. 191 



be evolved during the combustion of coal in a stove. But 

 what (he asked) is the source of electricity in this case ? Is 

 it combustion, the evaporation of the moisture, or the fric- 

 tion of the hot air on the interior of the pipe? 



EXPERIMENTS ON PHOSPHORESCENCE. 



(Proceedings of the American Philosophical Society, vol. ii, p. 46.)* 

 April IG, 1841. 



Professor Henry mentioned that he had recently repeated 

 some experiments of Becquerel and Biot on phosphorescence, 

 the results of which demonstrate the existence of an emana- 

 tion from incandescent bodies, particularly when in an 

 electrical state, of a character not heretofore known. He 

 promised to give a more full account of these at a future 

 meeting of the Society. 



[*The title-page of vol. ii, (comprising the proceedings from Jan., 1841, 

 to May, 1843,) bears date 1844.] 



