152 
DR. DAUBENY ON THE ACTION OF LIGHT UPON PLANTS, 
Now it remained to be seen, with which of the above scales the power of occasioning 
a decomposition of carbonic acid in the vessels of the plant, and of forwarding those 
other functions of vegetable life which depend upon light, most nearly corresponded. 
For this purpose, a certain number of fresh leaves, which presented in each case 
an extent of surface as nearly as possible equal, and had been previously ascertained 
to give out equal quantities of oxygen, were introduced severally into jars, filled M T ith 
water impregnated with carbonic acid gas, placed on the surface of a pneumatic 
trough, and exposed for a certain time to the influence of the solar rays. 
The jars, in which the leaves thus selected stood, were severally covered over by a 
wooden screen, which intercepted all light from the included jar, excepting in front, 
where a frame was fitted to it of a nature calculated to support, either a circular pane 
of glass, or a flat bottle of corresponding dimensions. 
By fixing into the frame the various coloured media with which it was intended to 
operate, 1 was enabled to ascertain the influence which the light transmitted through 
each might exert upon the plant included. 
From a variety of experiments, which it seems unnecessary to detail, in as much as 
they merely tend to confirm the statements of preceding observers, it appeared, that 
the kind of leaf selected made but little difference in the result. I therefore con- 
tented myself with selecting such, as could be procured most readily, and in the 
freshest condition. 
