166 PHOSPHORESCENCE. LECT. VIII. 



acid, in the proportion of 1 to 9, forms a medium in which 

 the phosphorescence continues for several hours. We may, 

 therefore, conclude, that it is in consequence of some altera- 

 tion in the phosphorescent matter, that this ceases to glow 

 after it has been for some days in pure oxygen, one portion 

 only of which has been replaced by carbonic acid. 



I examined the hydrogen in which I had kept several 

 glow-worms for the space of twenty-four hours, and in 

 which they had glowed for a few minutes only. The follow- 

 ing is the result obtained when the gas was pure, and the 

 experiment was conducted over mercury; the bell-glass 

 being carefully filled by inverting it two or three times, in 

 order to get rid of all the air adhering to the glow-worms ; 

 the volume of the gas was slightly augmented : with 8 cubic 

 centimetres of hydrogen, I obtained an excess of 0*2 cubic 

 centim. which was absorbed by potash. Thus, then, the 

 insects produce carbonic acid, which must either be formed 

 by the union of carbon with the oxygen remaining in the 

 tracheaB, or exist ready formed in the animals. When the 

 luminous segments alone are placed in hydrogen, with due 

 precaution, they glow for a few seconds only and the gas 

 is not altered. 



Sthly. Heat, within certain limits, augments the light of 

 the phosphorescent matter ; cold has a reverse effect. 



9thly. When the heat is too strong, the phosphorescent 

 matter becomes altered, as it also does when placed in the 

 air or in any gas whatever for a certain length of time. This 

 undoubtedly is the reason why these insects cannot live in 

 all climates, and why they shine only during certain months 

 of the year. 



lOthly. The phosphorescent matter, when thus altered, 

 is no longer capable of emitting light or of becoming lumi- 

 nous. 



. These conclusions evidently prove the nature of the 



