46 M7'. James Rice on 



stresses which are quite independent of the body's state of 

 motion, and which exist whether it is at rest at or in motion 

 through the position or configuration considered. Once more the 

 mathematician teaches us how to measure the amount of potential 

 energy which a body in one position possesses in excess of what it 

 possesses in another, viz., by the mechanical work of the forces 

 as the body passes from the first — and more advantageous — 

 position to the second — and less advantageous — position. The 

 formulae obtained vary with the nature of the forces involved 

 and the particular laws which connect the magnitude of the 

 forces with the relative position of the body. In one very 

 important case, the energy of a raised mass, the measure is 

 obtained by multiplying the weight by the height, and perhaps by 

 a numerical factor suitable to a special unit of energy. In 

 another case, the energy of a stretched string, the result depends 

 on the tension and the elongation of the string — half their pro- 

 duct giving the energy of strain. 



It used to be urged against the workings of the scientific 

 mind that it sought to give a "mechanical" explanation to the 

 universe and to life itself — the implication being that in so 

 doing it affected to regard living matter as a "dead machine," 

 an automaton without emotions or feelings. The implication 

 was, of course, false, but the original statement contained an 

 element of truth in so far as there has always been on the part 

 of the scientist an effort to explain all physical and che^nical 

 changes in terms of movement of matter, especially matter in 

 the molecular, atomic or subatomic form ; such movement being 

 always subject to the dynamical laws, which were first propounded 

 clearly by Newton, and whose consequences were fully worked 

 out by the great mathematicians of the 18th and early 19th 

 century. One of the deductions from these laws establishes the 

 existence of an exact equivalence between the two forms of 

 energy just dealt with, whenever the forces involved are of a 

 conservative nature — in practice this would exclude the action 

 of forces arising from friction and percussion. AVhenever the 



