THE FORCE INCLUDED IN PLANTS. [MEMOIR XI. 



of heat, the energy it had absorbed. As, however, I am 

 here speaking of the source of light in flames, in which 

 carbon takes the leading and hydrogen only an indirect 

 or subordinate part, it is not necessary to trace in further 

 detail the action of the latter element. 



A very interesting illustration of the principles here 

 under consideration occurs in the case of the decomposi- 

 tion of water by an electric current. The constituents 

 of the water, hydrogen and oxygen, are set free in the 

 gaseous form. But for them to assume that form they 

 must be furnished with caloric of elasticity. The current 

 supplies them with this, and, indeed, the decomposition 

 can only go on at the rate which is regulated by that 

 supply. The heat they have thus assumed remains in- 

 sensible in them, imparting to them their elastic or gas- 

 eous condition, until they are caused to reunite and re- 

 form water, when it is at once given up. The part that 

 is played by that portion of the electric current which is 

 thus transformed into heat and furnishing their caloric 

 of elasticity to the evolving gases is absolutely essential 

 to the decomposition has been hitherto too much over- 

 looked by chemists. 



Nature thus offers us in the instance we have been 

 considering in this Memoir a striking illustration of the 

 transmigration of matter and of force. Plants obtain 



o 



carbon from the atmosphere ; it constitutes the basis of 

 their combustible portions. Sooner or later it suffers ox- 

 idation, turns back into the condition of carbonic acid, 

 and is diffused again into the atmosphere. There is a 

 never-ending series of cycles through which it runs : now 

 it is in the air, now a part of a plant, now back again 

 in the air. And the same is true as regards the energy 

 with which it was associated. Derived from the sun- 

 beam, it lay hidden in the plant, awaiting re-oxidation ; 

 then it was delivered, escaping under the form of heat or 



