CHAPTER II 

 THE STORAGE OF ENERGY 



" All forces of the earth, all manifestations of life are modulations and variations 

 of the same heavenly melody which proceeds from the smi." Tyndall. 



All life processes demand for their continuation and mainten- 

 ance a continuous supply of matter and energy. As far as 

 matter is concerned, there is a closed cycle. Animals feed on 

 plants, and plants feed on the products of animal metabolism and 

 disintegration. Energy, however, must be supplied from outside 

 the cycle. The one essential physical factor that makes the 

 process possible is the supply of energy as simlight to the plant. 



The ultimate source of all the energy upon which existence on 

 this planet depends is the sun. (One need not here enter on the 



IZOOO 



lOOOO 



8000 



6000 



■*ooo 



20 oo 



.y^ 



HEftT 



VISUAL 



ACTINIC 



Fig. 1. — Cui-ves showinsi relative energy and hiuiiiiusity uf dittereut regions of tlie 

 spectrum. (Abney.) Tlie wave-lengths ^are given in Angstrom units. An Angstrom 

 unit (A.T'.) = one ten millionth of a millimetre = 0-1 /x/x 



interesting question of how the sun evolves energy ; see Soddy, 

 Matter and Energy, Chap. X.) As far as we know, the higher 

 forms of life are unable directly to use either heat or light as 

 sources of bodily energy. Some of the lower forms of animal life 

 may have this power ; plants certainly have. As we shall see 

 later, light may act as trigger-energy starting a series of changes 

 in matter and its energy content whereby a liberation of free energy 

 is effected. This free energy will then be available for work. 



The green plant is able to collect and conserve a portion of the 

 stream of energy emitted from the sun. This it does by virtue of 

 its content of a green pigment chlorophyll dissolved in the lipoids 



14 



