Prof. Draper on the Phosphorescence of Bodies. 91 



4th. Is phosphorescence accompanied ivith a development of 

 electricity ? 



It has ah-eady been stated^ that the experimenters of the last 

 century paid a good deal of attention to this point. Dnfay 

 estabUshed the fact, that though in many cases of phosphores- 

 cence there is a development of electricity, there are many others 

 in which the light seems to be wholly unattended by any dis- 

 turbance of that kind. 



I have repeated some of these experiments, and with the same 

 results, if proper care be taken to avoid friction, and other ob- 

 vious causes of electric excitement. Thus a flat piece of chloro- 

 phane, phosphorescing powerfully, was put on the cap of a very 

 delicate gold-leaf electroscope, but no distm-bance whatever was 

 perceptible. 



A large ciystal of iluor-spar was made to phosphoresce bril- 

 liantly along a line about half an inch in length, by passing the 

 spark of a Leyden jar between two blunt iron wires, the ends of 

 which were that distance apart, and resting on the face of the 

 ciystal. Over this line of blue light, which was pretty sharply 

 marked, and which lasted for several minutes, a delicate hair 

 was held. This would ha\ e been readily attracted and repelled 

 by the feeblest excitation on sealing-wax, but in this case it 

 wholly failed to yield any indication whatsoever. 



In connexion with the foregoing experiments I may mention 

 some miscellaneous facts. I made some attempts to deter- 

 mine whether phosphorescent bodies, in the field of a powerful 

 electro-magnet, would exhiljit any change of property. Six 

 Grove's jjairs were made to magnetize a good electro-magnet ; 

 the power they could give to it would enable the keeper to sup- 

 port about half a ton. Between its polar piece, chlorophane, 

 Canton's phosphorus, &c., which had been made to glow by ex- 

 posure to a Leyden spark, were placed. But whether the mag- 

 netism was on or not, there was no difference in the light. 



It was also found that the electric spark from a contact- 

 breaker would communicate phosphorescence to all the various 

 bodies in use in these experiments ; and that, up to a certain 

 point, the intensity of the light increased with the number of the 

 sparks received. 



Phosphorescence is not communicaljle from one body to an- 

 other. Having provided two polished plates of fluor-spar, one 

 of them was made to gh)w by an electric spark, and the other 

 was immediately ])ut upon it. No communication of ))h()spho- 

 rescence took place ; tiie second piece remained perfectly dark. 



Some authors state; that fluor-spar docs not become phospho- 



