subscriptions to build this or that statue, for the support of scientific work or philanthropies, or even through thefts: "Quelquefois meme c'est par des vols ou se montre la perversion d'un esprit sectaire, l'aberration et la profondeur de ses convictions passionees." Commonly, indeed, money performs even this function, that of measuring currents of belief, passion, enthusiasms, etc., through the process of exchange, and, ordinarily, it is difficult to get any single current separately. We simply get the resultant of an equilibrium of a complex of forces in economic values. But sometimes a single factor stands out so prominently that we can abstract from the rest, and let money changes measure changes in it alone. For example, during the three days of the battle of Gettysburg, the premium on gold, as measured in terms of Federal paper, fell from forty-five per cent to twenty-three and a fourth per cent.[205] For the market, this means simply a change in the economic value of Federal paper. But for one who cares to look even superficially behind the scenes, it means an increased volume of belief in the triumph of the Federal arms--a belief that at once affected economic values, and was measured in terms of money. Or, the economist may abstract a single legal factor, as a tax law, and measure its influence on the assumption that the rest of the situation is constant, in the well-known laws of shifting and incidence. Such clean-cut instances are not the rule, however. The organic complexity of the social forces lying back of economic values makes it difficult to disentangle single elements, and measure their force. For one thing, variations in one factor usually mean movements in the others. If we may borrow terms from chemistry, while the economist may give us a _qualitative_ analysis of these forces, it is hard for him to give us a _quantitative_ analysis. And the characteristic of pure economic theory has been its effort to get quantitative, quasi-mathematical laws. The "pure theorist," therefore, does well to start with a quantitative value concept (a convenient shorthand or symbol for the infinite complexity that lies behind it), a value quantity in which the net outcome of social interactions does precisely manifest itself, and study the laws which it manifests. His chief interest is, not in the origin of economic value itself, but in the changes in quantities in value in different goods and services as these manifest themselves in the market, and submit themselves to economic measurement. In a word, his chief interest is, not in value, but in _prices_.[206] And the great bulk of pure economic theory, and practically all that is of greatest importance in pure theory, is in the theory of prices, and not in the theory of value. Lest I be misunderstood, the qualification must be repeated: prices here mean, not money-prices, but prices in the generic sense. In this sense of the word price, it is just as