THE DOGMA OF EVOLUTION 



earth by an external impulse, or it is given kinetic en- 

 ergy if its velocity is increased; the body maintains 

 this energy and may, later, give it back to other 

 bodies. Let us see if the analogy is one of words only, 

 or whether memory can be expressed in terms of en- 

 ergy. Suppose, for example, I see a pencil and that 

 a chemical change of the retina occurs. As a result, 

 a definite portion of the brain may be physically 

 changed. If memory be a physical phenomenon I 

 can imagine no other physical change in the brain 

 than such a rearrangement in space of molecules or 

 atoms as will increase the potential energy of the por- 

 tion of the brain just as would be effected in it by an 

 increase of heat. That is, the sight of the pencil causes 

 a molecular change in a portion of the brain and 

 increases its potential energy. If, tomorrow, circum- 

 stances arise such that the appearance of the pencil 

 is recalled in my mind, I can think of no other ex- 

 planation but that I have used some of the potential 

 energy which was stored up by the original stimulus 

 of seeing the pencil. Each time, then, that I remem- 

 ber the pencil I use a portion of this potential energy 

 until, if the process were repeated often enough, the 

 portion of the brain would return to its original state. 

 As a physical process memory would grow fainter the 

 oftener the faculty is used, whereas psychologically 

 memory increases with use. It really seems as if not 

 only our mental actions were not measurable in phys- 



1:2683 



