Prof. Draper on the Phosphorescence of Bodies. 89 



surface of which was finely polished, was made to phosphoresce 

 brightly along a given line, determined by the blunt ends of two 

 iron wii'es, which served as a discharger, and were placed near 

 to the poUshed surface. The spar was forthwith suspended in 

 the mercui'ial box of a Daguerreotyjie apparatus, and kept there 

 for an hour. The mercury was found condensed upon it faintly, 

 in the manner it would have been on a Daguerreotyjie plate, 

 especially on and in the vicinity of those parts that were more 

 immediately exposed to the spark. This, therefore, seems to 

 prove, that there is in these cases a molecular modification of the 

 shinmg sm-face. 



3rd. Wlien a phosphorescent body gloivs, does it likeivise emit 

 heat? 



A veiy thin bulb, half an inch in diameter, Avas blown on a 

 piece of thei"mometer-tu.be ; and after being washed over with 

 gum-water, finely-powdered chlorophane was dusted on it till it 

 was neatly coated all over. A di-op of water was then introduced 

 into the tube to serve as an index. Although the instrument 

 was veiy sensitive to heat, when the chlorophane was made to 

 shine by a powerful electric spark passed 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. 



A modification of this experiment was tried, which appeared 

 to offer several advantages. The instrument which had been 

 used to determine whether any dilatation of a phosphorescent 

 body took place, as described above, was emptied of its water, 

 and a single drop put in the index-tube. It was supposed that, 

 when the rays of the electric spark passed through the quartz 

 and made the phosphorus shine, if its temperature rose, the sur- 

 rounding air in the tube warmed thereby would expand, and a 

 movement of the index liquid in the thermometer-tube take 

 place. But in several trials, in which different bodies, chloro- 

 phane, Canton's phosphorus, &c., were employed, the results 

 were uniformly negative ; for though these different substances 

 glowed splendidly as soon as the spark passed, there was not the 

 smallest rise of temperature perceptible. 



A further attempt was made as follows : — The disc of quartz 

 being removed, it was replaced by a cork, through which a pair 

 of iron wires, to serve as a discharger, ])assed air-tight, and de- 

 scended to within a short distance of the phosi)horus. A suffi- 

 cient period of time was allowed, in various repetitions, for the 

 index liquid to come to rest. It was ho])ed that this form of 

 experiment would have advantages over the ))reeeding, because 

 the discharging wires could be brought nearer to the |)hosphorus, 

 and the effect take place without the intervention of the quartz. 



