HEAT AND MOTION, AND POLITICAL ECONOMY. 331 



mination of a value unit, for only thus can we know the value ; or, 

 to speak more exactly, only thus can we conceive the labor expended 

 on the thing. We must be able to say, not only that labor has been 

 expended on the thing, but also how much. 



Marx was the first to essay the determination of a value-unit. This 

 he found in a fixed term of " labor-time," usefully expended in the 

 work. But time is no measure. The measure must be a thmg, if it 

 is to be cognizable at all, and such a measure is presented to us only 

 in Mayer's law. 



For, if work be equal to motion, and motion to heat, then a given 

 amount of work (task) can also be regarded as equal to the amount 

 of materials expended in producing the heat required for such work 

 (motion). And hence, just as we compare a given net amount of efi'ect 

 from a steam-engine with the coal expended, so may we compare a 

 certain amount of work with the amount of food expended in produc- 

 ing it ; and since wheat contains all the essential elements of nutrition, 

 we may compare a task with the quantity of wheat expended in per- 

 forming it. Where a day's wages is paid in the shape of a day's 

 provisions we have a crude example of the application of this theory. 



Hence, as natural forces are gratuitous, the value of a thing ex- 

 presses the amount of food expended in its production ; and the value- 

 unit is a fixed quantity of this food, say so much as is won by a day's 

 work. 



Exchange of values is effected with the aid of a thing in which are 

 expressed the food-units required for its production; this is metal 

 coin. Hence exchange-metal is both value and an index of value. 



Mayer's law furthermore gives the law of wages. The workman 

 must get back what he has expended in his labor in the shape of food ; 

 and this expenditure must be supposed to cover the cost of his bring- 

 ing up and development, as also provision against old age when he can 

 no longer work. 



The idea of capital, too, and especially of the justification {Berech- 

 tigung) of capital, falls under Mayer's law. Experience teaches that 

 the amount of food-material gained by labor is in excess of that 

 expended in labor. This excess is capital in the strict sense, perfectly 

 justified capital. 



In virtue of the law of equal wages for equal work, every one, even 

 though he does not produce (if we may so speak) food-stufis, is enti- 

 tled to the same surplus in recompense (food-stuffs) that he would 

 have earned by work expended in the production of food-stuffs. 



Perhaps it will be objected that Mayer's law applies to bodily 

 labor, not to mental ; but here, too, it holds good. The natural forces 

 are gratuitous : it is only human labor that produces value. Now to 

 natural forces belong not only the materials of the animal, vegetable, 

 and mineral kingdoms, but also intellectual qualities, even genius 

 itself. 



