MEMOIR VIII.] THE PHOSPHORESCENCE OF BODIES. 



which a pair of iron wires to serve as a discharger passed 

 air-tight, and descended to within a short distance of the 

 phosphorus, sufficient time was allowed in various repeti- 

 tions for the index liquid to come to rest. It was hoped 

 that this form of experiment would have advantages over 

 the preceding, because the discharging wires could be 

 brought nearer to the phosphorus, and the effect take 

 place without the intervention of the quartz. When 

 the spark was made to pass, there was a great move- 

 ment in the index tube, as in the instrument known as 

 Kinnersley's electrometer, but the liquid immediately re- 

 turned to within a short distance of its first place ; then 

 a slow dilatation occurred, as though the air was gradu- 

 ally warming. Thus in one experiment the liquid stood 

 at 24, after the explosion it returned to 26, and then 

 there was a gradual dilatation to 32. 



To eliminate the various disturbing causes in this ex- 

 periment, it was repeated many times, the spar being al- 

 ternately introduced into the glass tube, and alternate- 

 ly removed. It was found that whenever the spar was 

 present the gradual dilatation alluded to took place; 

 but when the spar was not in the tube, instead of a 

 dilatation, there was a gradual contraction until the in- 

 dex liquid recovered its original position. 



From this it appears that with the evolution of light 

 there is a feeble extrication of heat. 



The quantities of heat thus liberated are so small, and 

 the causes of error are so numerous, that I endeavored 

 by other methods to obtain more trustworthy results. 

 Thus I attempted to determine the surface temperature 

 of a flat piece of chlorophane while phosphorescing by 

 means of the thermo-electric multiplier. The thermo- 

 pile was placed in a vertical position, and the spar 

 having been attached to a piece of wood, which served 

 as a handle, intense phosphorescence was communicated 



