Although the fiscal interests are great, yet in every important country except England the receipts from this source are not regarded as of any greater importance than the effects upon the industries of the country. There are then two sides from which these taxes must be studied : (1) From the side of revenue-yielding capacity; (2) from the side of the " protection " afforded the industries of the country which levies them. While it would be undesirable to introduce a full discussion of the far-reaching economic effects of protective duties upon industries and commerce in a treatise on finance, yet a brief statement of these effects and of the main reasons which have led great nations to adopt these taxes is essential to an understanding of their nature. It is as essential to know how and why protective duties are intended to alter the existing economic conditions, as it is to know how and why the income tax, for example, is supposed to leave them unaltered.¹