6 LAWS OF ENERGY 



the energy thus Hherated is, iiv theory, available for work. In 

 practice, it is found that all this surplus energy cannot be recovered 

 as work. No system is absolutely isolated and, though the total 

 cosmical energy may be constant, its distribution and its state 

 may alter. Some of the freed energy is always converted into heat, 

 part of which is diffused among surrounding objects and is thus 

 lost, as far as work is concerned. The quantity of energy is not 

 decreased, but its dispersion is so great that in quality it has not 

 sufficient potential gradient to be of use. As an example of 

 dispersion of energy, consider how waves in ether, e.g. light or the 

 longer (wireless) waves, fall away in strength in widening concentric 

 zones as their influence spreads from the source, till at infinite 

 distance the most sensitive apparatus can only with difficulty 

 detect the disturbance. The wave energy has been so spread that 

 it may be disregarded. 



The second law is usually worded, " The entropy of an isolated 

 system tends to a maximum." Entropy is a function which, while 

 theoretically of great value as indicating the direction in which 

 chemical or other processes take place, cannot be directly measured, 

 ^'urther, one never has, in Biology, to deal with an isolated 

 system. The difficulty as well as the great interest of our science 

 depends on the close interrelation and co-ordination of all the 

 systems in it. A simple expression of the law, and one suited 

 to our purpose, would be, " Every change takes place at the cost 

 of a certain amount of available energy." The amount of energy 

 so " degraded " during a transformation from one form to another 

 may be taken as an inverse index of the efficiency of the transform- 

 ing mechanism. 



States of Energy. 



A substance may be endowed with kinetic energy, or with 

 potential energy, or with both. Kinetic energy is directly avail- 

 able for work, potential energy requires the use of some kinetic 

 energy to liberate it. The energy of a substance may be in the 

 motion of the substance itself or in the motion of the ultimate 

 particles composing it. This kinetic energy and its value depend 

 on the mass of the substance and the rate at which it moves or 

 at which its particles vibrate. 



Potential energy, on the other hand, is said to be possible to 

 a substance in virtue of its configuration, i.e. position, composi- 

 tion, history, etc. A quantity of energy that may be lueasured 

 is stored up (or rendered passive in some way), and this same 

 quantity is theoretically recoverable in a measurable form. It 

 may not be apparent how energy is stored up, but it may be demon- 



