ii THE PLANT AND THE ANIMAL 121 



the necessity of physical forces the largest possible amount 

 of indetermination. This effort cannot result in the 

 creation of energy, or, if it does, the quantity created 

 does not belong to the order of magnitude apprehended 

 by our senses and instruments of measurement, our ex 

 perience and science. All that the effort can do, then, is 

 to make the best of a pre-existing energy which it finds 

 at its disposal. Now, it finds only one way of succeed 

 ing in this, namely, to secure such an accumulation of 

 potential energy from matter, that it can get, at any 

 moment, the amount of work it needs for its action, 

 simply by pulling a trigger. The effort itself possesses 

 only that power of releasing. But the work of releasing, 

 although always the same and always smaller than any 

 given quantity, will be the more effective the heavier 

 the weight it makes fall and the greater the height or, 

 in other words, the greater the sum of potential energy 

 accumulated and disposable. As a matter of fact, the 

 principal source of energy usable on the surface of our 

 planet is the sun. So the problem was this : to obtain 

 from the sun that it should partially and provisionally 

 suspend, here and there, on the surface of the earth, its 

 continual outpour of usable energy, and store a certain 

 quantity of it, in the form of unused energy, in 

 appropriate reservoirs, whence it could be drawn at the 

 desired moment, at the desired spot, in the desired 

 direction. The substances forming the food of animals 

 are just such reservoirs. Made of very complex mole 

 cules holding a considerable amount of chemical energy 

 in the potential state, they are like explosives which only 

 need a spark to set free the energy stored within them. 

 Now, it is probable that life tended at the beginning to 

 compass at one and the same time both the manufac 

 ture of the explosive and the explosion by which it 



