While the equation of exchange is, if we choose, a mere "truism," based on the equivalence, in all purchases, of the money or checks expended, on the one hand, and what they buy, on the other, yet in view of supplementary knowledge as to the relation of _M_ to _M'_, and the non-relation of _M_ to _V_, _V'_, and the _Q_'s, this equation is the means of demonstrating the fact that normally the _p_'s vary directly as _M_, that is, demonstrating the quantity theory. To throw away contemptuously the equation of exchange because it is so obviously true is to neglect the chance to formulate for economic science some of the most important and exact laws of which it is capable. We may now restate, then, in what causal sense the quantity theory is true. It is true in the sense that one of the _normal effects of an increase in the quantity of money is an exactly proportional increase in the general level of prices_. I have no desire, as some one has humorously suggested, to hide behind an equation, but I do find it necessary to take refuge behind my book on the _Purchasing Power of Money_. So many new questions have been asked that, in the few moments at my disposal, I could not answer them all satisfactorily. I believe they have all been answered in the book referred to. For instance, a chapter has been devoted to transition periods in which it has been shown, as Professor Taussig has suggested, that during transition periods an increase in _T_ may cause an increase in _M'_. THE TESTIMONY OF RICARDO [78]Let us suppose that the circulation of all countries were carried on by the precious metals only, and that the proportion which England possessed were one million; let us further suppose, that, at once, half of the currencies of all countries, excepting that of England, were suddenly annihilated, would it be possible for England to continue to retain the million which she before possessed? Would not her currency become relatively excessive compared with that of other countries? If a quarter of wheat, for example, had been both in France and England of the same value as an ounce of coined gold, would not half an ounce now purchase it in France, whilst in England it continued of the same value as one ounce? Could we by any laws, under such circumstances, prevent wheat or some other commodity (for all would be equally affected) from being imported into England, and gold coin from being exported? If ... the exportation of bullion were free, gold might rise 100 per cent.; and for the same reason, if 35 Flemish schillings in Hamburgh had before been of equal value with a pound sterling, 17-1/2 schillings would now attain that value. If the currency of England only had been doubled, the effects would have been precisely the same.