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grow, but it forms no woody matter, it acquires no colour ; even 
in shade it grows slowly and weak. In sunshine it glows with 
colour, and its frame is strengthened by the deposition of woody 
matter eliminated from the carbonic acid of the air in which it 
grows. A momentary digression will make one point here more 
clear. Men and animals live by consuming the products of the 
vegetable world. The process of supporting life by food is 
essentially one of combustion. The food is burnt in the system, 
developing that heat which is necessary for life, and the living 
animal rejects, with every expiration, the combinations, princi- 
pally carbonic acid, which result from this combustion. This 
carbonic acid is inhaled by the plant ; and, by its vital power, 
excited by sunshine, it is decomposed ; the carbon forms the 
ligneous structure of the plant, and the oxygen is liberated to 
renew the healthful condition of the atmosphere. Here we see 
a sequence of changes analogous to those which have been shown 
to be a law of electricity. 
Every equivalent of matter changing form in the sun sends 
forth a measured volume of sunshine, charged with the orga- 
nising powers as potential energies. These meet with the 
terrestrial matter which has the function of living, and they 
expend themselves in the labour of producing a quantity of 
wood, which represents the equivalent of matter which has 
changed form in the sun. The light, heat, chemical and elec- 
trical power of the sunshine have produced a certain quantity 
of wood, and these physical energies have been absorbed — used 
up — in the production of that quantity. How, we learn that 
a cube of wood is the result of a fixed measure of sunshine : 
common experience teaches us that if we ignite that wood it 
gives out in burning, light and heat ; while a little examination 
proves the presence of actinism and electricity in its flame. 
Philosophy teaches us that the powers set free in the burning 
of that cube of wood are exactly those which were required for 
its growth, and that, for the production of it, a definite equiva- 
lent of matter changed its form on a globe ninety millions of 
miles distant from us. 
Myriads of ages before man appeared — the monarch of this 
world — the sun was doing its work. Vast forests grew, as they 
now grow, especially in the widespread swamps of the tropics, 
and, decaying, gathered into thick mats of humus-like substance. 
Those who have studied all the conditions of a peat morass, 
will remember how the ligneous matter loses its woody struc- 
ture in depth — depth here representing time — and how at the 
bottom a bituminous or coaly matter is not unfrequently 
formed. Some such process as this, continued through long 
ages, at length produced those extensive beds of coal which are 
so distinguishingly a feature of the British and American coal- 
