Q.Irving Fisher's Quantity Theory of Money was popularized in :

The Quantity Theory holds that, other things equal, the price level varies directly and proportionately with the quantity of money. Fisher's transactions approach expresses this as the equation of exchange $MV = PT$ (money × velocity = price level × transactions); with V and T constant, P is proportional to M. The Cambridge cash-balance approach expresses the same idea from the demand side as $M = kPY$, where k is the fraction of real income people wish to hold as cash and $k \approx 1/V$. Fisher emphas …