490 



All;. .1. I!. LAWES, DR. GILBEIIT, \\\> DB. PTJGH OS 



plant were operated upon ai the same time. Both were prepared in the shade; an 



then the vessels containing them were each entirely excluded from the light, by meant 

 (if ;i thick paper covering. In this condition each was attached to a Torricellian ex- 

 hauster*. The paper was then removed from one of tie to expose it. 

 with its contents, to the direct rays of the sun ; the other vessel, with its enclosed plant, 

 remaining covered. The exhaustion of both was then commenced immediately, and the 

 action continued for half an hour. 



The follow in- Table shows the results obtained in this manner, in sunlight, and in 

 the- dark, respectively. 



Table IV. — Showing the amount and composition of the gas evolved, during half an 

 hour, into a Torricellian vacuum, by duplicate quantities of plant, both kept in the 

 dark for some time before commencing the exhaustion, then one exposed to sun- 

 light, and the other kept in the dark, during the process. 



(1858.) 



The amounts of carbonic acid and oxygen recorded in the Table, indicate very clearly 

 the ready transformation of the one into the other — or, rather, the transformation of 

 carbonic acid into a solid carbon compound, and free oxygen. In reference to the 

 question we are considering, these results have a high importance, as showing the great 

 reducing-force manifested under the influence of the sun's rays, by which the carbonic 

 acid is so suddenly reduced. 



* This term, for convenience, vre apply to the apparatus which has been described at p. 4S7, by which the 

 plant in the vessel, fig. 7, Plate XII., is exhausted. 



