[203] Senior’s rent to skill is an entirely different form of surplus from that due to the excess of utility produced above disutility incurred in the “earlier” parts of the working day of all labor. So long as the length of the working day is left to the worker himself, he will stop when the terminal utility and disutility are equivalent. All previous parts of the day produce a surplus of utility. This is the surplus which occupies an important place in J. B. Clark’s theory of value. Compare Marshall’s “producer’s” and “consumer’s rents.” Senior’s “rent to scarce natural talents” is explicable only on the supposition that the disutility endured and the return of utility enjoyed by a skilled laborer can be compared with the same quantities for an unskilled laborer. Senior means merely that skilled laborers obtain higher returns at lower sacrifices as compared with unskilled. A certain part of the return enjoyed by the skilled laborer is equivalent to that enjoyed by the common worker; the part in excess of this is the rent. Senior considers it analogous to the rent which goes to lands of superior fertility. Further consideration will be given in a later section to the relation of skill to the labor theory of value. [204] January, 1894, p. 218. [205] In the _Journal of Political Economy_, vol. ii, p. 561. [206] _Theoretische Socialökonomik_, 1895, vol. i, p. 205. [207] _Theoretische Socialökonomik_, 1895, vol. i, p. 233. Dietzel supposes that Smith conceived of labor solely as “_Unlust_,” but in this he is clearly mistaken. See _ante_, chapter iv. [208] See _ante_, p. 86. [209] For an excellent discussion of the term “esteem value” see Walsh, _The Measurement of General Exchange Value_, pp. 1-6. The writer is greatly indebted to Walsh’s discussion of the value concept. The two kinds of value here distinguished are the same as those designated objective exchange value and subjective value by the Austrian writers. [210] As, for instance, by Pantaleoni, _Pure Economics_, p. 123. [211] This definition by itself does not of course make clear the ultimate source of this power. For proximate and practical purposes the weight of a pound nugget of gold might well be defined as its power to counterbalance in the scales a certain piece of metal, the standard troy pound. This definition contains no hint of the common source of the counterbalancing power of both weights. In the same way the above-given definition of exchange value ignores a certain common source of all exchange values. [212] For a discussion of certain avoidable objections that have been made to the concept of purchasing power, see Walsh, _op. cit._, pp. 7 and 8. [213] It takes little discernment to see that this statement is not equivalent to saying that the formulation of a theory of value is a greater accomplishment than was the formulation of the law of gravitation. The writer does not plead guilty to implying that.