The Wealth of Nations by Part 2 Chapter 5 Page 32

Three times a greater capital must in both cases be employed in order to exchange a certain value of British manufactures for a certain quantity of flax and hemp than would have been necessary had the manufactures and the flax and hemp been directly exchanged for one another.

The whole capital employed, therefore, in such a round-about foreign trade of consumption will generally give less encouragement and support to the productive labour of the country than an equal capital employed in a more direct trade of the same kind.

Whatever be the foreign commodity with which the foreign goods for home consumption are purchased, it can occasion no essential difference either in the nature of the trade, or in the encouragement and support which it can give to the productive labour of the country