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700 Professor Jevons has been at some pains to investigate the bibliography of the subject, and finds it surprisingly full and of considerable value.

It appears from his researches that the theory, as stated by him, and in a form closely resembling his, by M. Léon Walras, of Lausanne, has been anticipated in its chief features by Gossen, of Germany, and Cournot, of France. This is somewhat remarkable, as these writers worked not only independently of each other, but with little or no knowledge of what had been done by any others. They had, in fact, to begin at the beginning and work out the entire subject for themselves. Professor Jevons regards this independent arrival at substantially the same views of the "fundamental ideas of economics," by four different inquirers, as strong evidence of their probable truth. He appends to the present edition of his work a fuller list than was possible in the first of all the writers whose names he has been able to discover, who treat the science on this side, that future students may not remain in ignorance of what has been accomplished.

The present unsatisfactory state of economics is regarded by him as due to the failure, on the part of economists, to distinguish between several branches of knowledge which, though closely allied, are yet separate. There should be a distinction drawn between the abstract science which has to do with the fundamental relations of economic quantities and those special concrete sciences which depend upon it. The relation of this abstract science to the concrete ones he holds to be somewhat analogous to that between the science of mechanics and the physical sciences, all of which have their basis more or less in it. Pleasure and pain are, according to him, the ultimate factors with which economics has to deal, and how to increase the one and decrease the other to the greatest extent possible is the problem to be solved, or, stated more specifically, the problem is: "Given a certain population, with various needs and powers of production, in possession of certain lands and other sources of material; required the mode of employing their labor which will maximize the utility of the produce." In order to subject the science to his analysis. Professor Jevons introduces into economic quantities the physical conception of dimension. These quantities can then be treated geometrically, and their various relations expressed by formulas. A feeling, such as a pleasure or a pain, he considers possessed of two dimensions, intensity and duration, the amount of which can be varied by varying either or both of the factors. A curve whose ordinates correspond with the intensity of the feeling and the abcissas with its duration will express the law of the variation of the intensity, when this variation is continuous.

The relations of the various economic quantities involved would, in any case, be known when the elements of such a curve were determined, or, as the mathematicians say, when the form of the function is known. The agreement of the calculated result, when numerical data are introduced into the formulas, with the actual result, would be the verification of the formulas. Such numerical data, consisting mainly in "accurate accounts of the quantities of goods possessed and consumed by the community, and the prices at which they are exchanged," are not now easily attainable, and formulas can not, therefore, be at present verified. As these data become available, however, Professor Jevons thinks that the science can gradually be raised to the position of an exact one.

A large portion of the present work is devoted to the elucidation of the problem of exchange value, which is necessarily fundamental in any economic exposition. Exchange value, or, as he terms it, "the ratio of exchange," is held by him to be directly dependent upon utility and only ultimately upon cost of production. In his theory of utility he draws a distinction between the total utility of any commodity and its degree of utility at any point of supply, the person concerned being the sole judge in any case considered of what is or is not useful. In illustration, the total utility of such a thing as food is infinitely great, as it is necessary to life; but, when we have abundance, the utility of an addition is very small and may be zero. Considering the increase of supply to be made by adding increments of commodity, the degree of utility of the last increment added, or of that to be