On the other hand, a supposition that may clearly become a fact is a substantive thing, and logical inferences may be drawn from it, just as geometrical inferences may be drawn from a _supposed_ circle: the circle on the page is not a _perfect_ circle--no such circle was ever drawn--but _suppose_ it perfect, as it might possibly be, and argument becomes at once valid. Let us take another Monetary Conference at Paris in 1867 as an illustration: its judgment as voiced by Mr. Ruggles of New York was taken with logical propriety, when the great benefits of an international coinage of gold alone were argued and announced, because, while that was then a mere conjectural project, it was possible any day by mutual agreement among the nations to become a reality. An international coinage of gold is a simple question of equivalence of _weights_ in the coins of different countries: an equivalence of _values_ as between gold and silver coins for any great length of time is neither simple nor possible. (5) _Results measurable in numbers._ The four preceding logical processes of proof and construction Political Economy is glad to share with the other Moral Sciences, but this fifth and last one it has to itself alone, and this is its chief scientific advantage over them, and is consequently the main reason why it is already more advanced and more symmetrically developed than any of them. In common with them it has important subjective elements, such as Desires, Estimates, and Satisfactions; in marked advantage over them it has also objective elements, that can be weighed and measured and even hardened into statistics. Economics has an ever ready objective test, which mere mental and ethical and other moral processes never can have from their very nature. The _result_ of each and of all economic transactions may be measured by money, and put down in a ledger, and published to the world in the form of statistics. An economic blunder, whether in legislation or in private action, pretty soon proves itself to be such by the lessened gains of somebody, and these losses can be stated arithmetically; and similarly, an economic improvement evidences itself at once by increased gains coming to somebody; while it may take years and years to work out the results of an ethical mistake, and even then their amount can only be guessed at.