LECT. VIII CAUSE OF THE PHOSPHORESCENCE. 167 



phenomenon ; the production of light, by this insect, is 

 essentially connected with the combination of oxygen with 

 carbon, which is one of the elements of the phosphorescent 

 matter. 



Cause of the Phosphorescence. We must now inquire 

 how the phosphorescence is produced in the living animal: 

 under what circumstances it varies: and what is the struc- 

 ture of the luminous substance and of the parts which sur- 

 round it. 



Not due to Insolation. I placed some very lively and 

 shining glow-worms in a tin-box which closed accurately. 

 I opened it twenty-four hours afterwards, it being then two 

 hours after sunset. The insects appeared dead, but they 

 still emitted a feeble light. By warming them in my hand, 

 they began to move, and the light became more vivid. 



After thirty hours more, passed in this box, some of the 

 insects were dead, and no longer glowed ; in others, slight 

 phosphorescence was observed. This experiment supports 

 the opinions of Beccaria, Mayer, and other philosophers, 

 who regarded the phosphorescence of these insects as due 

 to insolation. 



But here is another experiment, the result of which is 

 clear and satisfactory. In the same box, which was pro- 

 vided with a double bottom, I put, in one compartment, a 

 great number of glow-worms, and in the other, a like quan- 

 tity, intermixed with some fresh cut grass, gathered in the 

 places where the insects had been found. At the expiration 

 of twenty-four hours I examined them; what I have before 

 related had happened to the first, but the others were still 

 lively and glowing. When we opened the box during the 

 day, in a dark place, we perceived their phosphorescence. 

 To avoid prolixity I shall content myself with saying, that 

 for nine days I preserved the glow-worms, with which the 

 grass had been intermixed; and during this period they 



