MATTER AND FORCE. 393 
The solid matter of which our lead and silver trees 
were formed was, in the first instance, disguised in a trans- 
parent liquid; the solid matter of which our woods and 
forests are composed is also, for the most part, disguised in 
a transparent gas, which is mixed in small quantities with 
the air of our atmosphere. This gas is formed by the 
union of carbon and oxygen, and is called carbonic acid 
gas. The carbonic acid of the air being subjected to an 
action somewhat analogous to that of the electric current 
in the case of our lead and silver solutions, has its carbon 
liberated and deposited as woody fiber. The watery vapor 
of the air is subjected to similar action; its hydrogen is 
liberated from its oxygen, and lies down side by side with 
the carbon in the tissues of the tree. The oxygen in both 
cases is permitted to wander away into the atmosphere. 
But what is it in nature that plays the part of the electric 
current in our experiments, tearing asunder the locked 
atoms of carbon, oxygen, and hydrogen? The rays of the 
sun. The leaves of plants which absorb both the carbonic 
acid and the aqueous vapor of the air, answer to the cells 
in which our decompositions took place. And just as the 
molecular attractions of the silver and the lead found ex- 
pression in those beautiful branching forms seen in our 
experiments, so do the molecular attractions of the liberated 
carbon and hydrogen find expression in the architecture of 
grasses, plants, and trees. 
In the fall of a cataract and the rush of the wind we 
have examples of mechanical power. In the combinations 
of chemistry and in the formation of crystals and vege- 
tables we have examples of molecular power. You have 
learned how the atoms of oxygen and hydrogen rush to- 
gether to form water. I have not thought it necessary to 
dwell upon the mighty mechanical energy of their act of 
combination; but it may be said, in passing, that the 
clashing together of 1 Ib. of hydrogen and 8 Ibs. of oxygen 
to form 9 Ibs. of aqueous vapor, is greater than the shock 
of a weight of 1,000 tons falling from a height of 20 feet 
against the earth. Now, in order that the atoms of oxygen 
and hydrogen should rise by their mutual attractions to 
the velocity corresponding to this enormous mechanical 
effect, a certain distance must exist between the particles. 
It is in rushing over this that the velocity is attained. 
