150 



THE PHOSPHORESCENCE OF BODIES. [MEMOIR VIII. 



by a Leyden spark, and the flat and shining surface 

 instantly put on the upper face^ of the pile. But there 

 was no movement of the astatic needles. 



Then, taking the stone by its handle, it was touched 

 with the tip of the finger for one second, and quickly 

 placed on the pile. A prompt movement of the needles, 

 amounting to four degrees, ensued. These experiments 

 were repeatedly tried, and the results were uniformly 

 the same. 



In Fig. 18, a a is the thermo-electric pile, b b the 



plate of chlorophane, c the 

 handle. 



On considering these re- 

 sults, it appears that as the 

 temperature of the air near 

 the multiplier in one of 

 the experiments was 53, 

 and the estimated temper- 

 ature of the skin 94, the 

 amount of heat which the 

 stone received from the 

 touch of the finger must 

 have been very small. I 

 made a comparative trial 

 by touching the bulb of a 

 thermometer for the same space of time, in the same 

 way, and found that there was a rise of about 1|. But 

 the conductibility of quicksilver is much greater than 

 that of chlorophane. 



It is to be inferred, therefore, that the quantity of 

 heat set free during phosphorescence is very small, 

 and that the surface of the chlorophane does not 

 change its temperature by one fourth of a degree ; 

 for had it done so, the multiplier would have instant- 

 ly detected it. 



Fig. 18. 



