LIGHT AND LIFE. 115 



Biot relates that in 1807, while at Formentera, em- 

 ployed in the work of extending the meridional arc, he de- 

 voted his leisure hours to the analysis of the gas contained 

 in the swimming-bladder of fishes living at different depths 

 in the sea. The oxygen required for these analyses was fur- 

 nished him by the leaves of the Cactus opuntia, which he 

 exposed in water to sunlight, under hand-glasses, ingen- 

 iously applying the discovery of Tngenhousz and Senebier. 

 It occurred to him one day to expose these leaves, rn_ a 

 dark place, to the illumination thrown by lamps placed in 

 the focus of three large reflectors, used for night-signals in 

 the great triangulation. He threw the light from three of 

 these reflectors on the cactus-leaves. The eye, placed in 

 this concentration of light, must have been struck blind, 

 Biot says. The experiment, kept up for an hour, did not 

 cause the release of a single gas-bubble. The glass was 

 then taken into the diffused light outside the hut. The sun 

 was not shining, but the evolution of gas took place at once 

 with great rapidity. Biot is a little surprised at the result, 

 and concludes that artificial light is impotent to do what 

 solar light can. The labors of Prillieux and other contem- 

 porary botanists have proved that all light acts on the res- 

 piration of plants, provided only it is not too powerful. 

 In Biot's case artificial light had no effect, because it was 

 far too intense. 



III. 



Lavoisier somewhere says : " Organization, voluntary 

 movement, life, exist only at the surface of the earth, in 

 places exposed to light. One might say that the fable of 

 Prometheus's torch was the expression of a philosophic 

 truth that the ancients had not overlooked. Without light, 

 Nature was without life ; she was inanimate and dead. A 

 benevolent God, bringing light, diffused over the earth's 

 surface organization, feeling, and thought." These words 



