that solar light is injurious to luminous animals, and 

 that in the case of one at least of those in the sea 

 it retreats from the surface. He tried electrical sti- 

 muli, but supposed them to act merely as mechanical 

 powers in educing light. 



Dr. Darwin supposed that the luminous exhibition 

 was owing to a secretion of some phosphoric matter, 

 and a slow combustion arising from this phosphorus 

 entering into combination with the oxygen inspired 

 the large spiracula in glow-worms seemed to give a 

 plausible colouring to the idea. It was also stated 

 that the light was increased by heat and oxygen 

 and extinguished by cold, also hydrogen, and carbonic 

 acid gas. We have clearly ascertained, however, ex- 

 perimentally, that the luminous matter does not con- 

 tain phosphorus that the light is not sensibly in- 

 creased by the purest oxygen and is not extinguished 

 in hydrogen and carbonic' acid gas. Spallanzani re- 

 .garded the luminous matter as a compound of hydro- 

 gen and phosphoretted hydrogen. Carradori found 

 that the luminous matter of the lampyris italica shone 

 in vacuo, oil, water, and under other circumstances, to 

 the exclusion of oxygen; and he and Brugnatelli con- 

 cluded, that the emission of light was owing to its ab- 

 sorption in food or air, and subsequently secreted in a 

 sensible form. Mr. Macartney ascertained that the 

 light of the glow-worm is not diminished by immersion 

 in water, or increased by the application of heat. We 

 find, on the contrary, that the maximum of brilliancy 

 is exhibited at 98 or 99 Fahrenheit, while it declines as 

 this temperature is increased. Foster and Spallanzani 

 assert that glow-worms shine more brilliantly in oxygen ; 

 while Beckerheim, Dr. Hulme, and Sir H. Davy, dis- 

 covered no such effect and to these last we adjoin 

 our testimony. Spallanzani and Dr. Hulme state that 



