of the various Forms of Energy. 279 



that body (by an amount not greater than the work clone); 

 hence this effect is called energy, and it is measured by the 

 quantity of work done in producing it*. Whenever work is 

 done by a body, i. e. anti-work done on it, its working-power 

 is found to be diminished (to - at least the extent of the work 

 done), and it is said to have lost energy — the energy lost 

 being measured, as before, by the anti-work done in destroy- 

 ing it. 



6. But in every action taking place between two bodies the 

 work is equal to the antiwork ( § 3) ; hence the energy gained 

 by the first body is equal to the energy lost by the second ; or, 

 on the whole, energy is neither produced nor destroyed, but 

 is simply transferred from the second body to the first. (Re- 

 member footnote to § 1.) 



To summarize then : — Work creates energy ; anti-work 

 destroys it ; so both together simply transfer it. Or, in other 

 words, the transference of energy requires a stress to act 

 through a distance, and involves therefore two equal opposite 

 works. If it were possible to obtain a force without its anti- 

 force, or if it were possible for two bodies exerting stress on 

 one another to move over unequal distances (§ 3), then it would 

 be possible to obtain work without the anti-work, and thus to 

 get a source of new energy (technically called the Perpetual 

 Motion); but, as a fact of experience, it is not possible. 



7. When work is done upon a body, different kinds of 

 effects can be produced, depending both on the nature of the 

 body and on the way in which the forces doing the work are 



* This definition of energy, as the effect produced in a body by an act of 

 work, is not so simple as the usual one — "the power of doing work ;" but 

 this latter definition seems a little unhappy. For energy is power of doing- 

 work in precisely the same sense as capital is the power of buying goods. 

 Now a sovereign has an infinite power of buying goods if it has any at all 

 — twenty-shillings worth being bought whenever it is transferred from 

 one man to another. The proper statement is that a sovereign usually 

 confers upon the man that possesses it a certain buying-power, which power 

 he loses when he lias transferred it ; and in this sense money is a power 

 of buying goods. It does not, however, necessarily confer upon its owner 

 any buying-power, because there may not be any accessible person to buy 

 from ; and if there be, lie may have nothing to sell. Just so with energy : 

 it usually, though not necesarily (see § 14), confers upon the body pos- 

 sessing it acertain power of doing work, which power it loses when it has 

 transferred it. The analogy here indicated will be found useful in teaching. 



Energy corresponds to capital. 



Doing work corresponds to buying. 



Doing antiwork corresponds to selling. 



The transfer of capital is accompanied by two equal opposite acts, buy- 

 ing and selling • and it is impossible for one to go on without the other. 

 Hence the algebraic sum of all the buying in the world is always zero : this 

 is the law of the conservation of capital. 



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