MR. W. WILSON LEISENRING'S interesting criticism of Prof. Soddy's economic views in his letter printed in NATURE of April 28, p. 571, appears to have over looked some of the most important causes of the present confusion in the world of economics. Among these I would put first the well-known psychological process of inversion, whereby the means is mistaken for the end, as exemplified by the old mercantile system or fallacy of representing the accumulation of gold and silver as the ultimate goal of commerce, and as being the true basis of national prosperity. Thus “protection”, “tariff reform” (and, indeed, most of the “labour” or trades union ideals) are no more than survivals of a belief that money, instead of being the mere instrument of exchange and a measure of market values, is of itself the end and purpose of all trade and labour activity.