148 THE PHOSPHORESCENCE OF BODIES. [MEMOIR VIII. 



3. When a phosphorescent body glows, does it likewise 

 emit heat? 



A very thin bulb, half an inch in diameter, was blown 

 on a piece of thermometer tube, and after being washed 

 over with gum-water, finely powdered chlorophane was 

 dusted on until it was neatly coated all over. A drop 

 of water was then introduced into the tube to serve as 

 an index. Although the instrument was very sensitive 

 to heat, when the chlorophane was made to shine and 

 emit a gorgeous emerald green light by the passage of 

 a powerful electric spark near it, no movement whatever 

 of the index ensued. From this it would appear that 

 the quantity of heat developed by phosphorescence must 

 be very small. 



In Fig. 17, a a is the glass bulb covered with a coat- 

 ing of powdered chlorophane, b 

 a drop of water serving as an 

 index. 



A modification of this exper- 

 iment, which appeared to offer 



several advantages, was tried. The instrument repre- 

 sented in Fig. 14 was emptied of its water, and a single 

 drop, h, put into the index tube. It was supposed that 

 when the rays of the electric spark passed through the 

 quartz and made the phosphorus shine, the air contained 

 in the tube, warmed thereby, would expand, and a move- 

 ment in the index liquid of the thermometer tube take 

 place. But in several trials, in which different bodies 

 chlorophane, Canton's phosphorus, etc. were employed, 

 the results were uniformly negative; for though these 

 different substances glowed splendidly as soon as the 

 spark passed, there was not the slightest rise of tem- 

 perature perceptible. 



A further attempt was made as follows : The disk of 

 quartz being removed and replaced by a cork, through 



