The Wealth of Nations by Part 5 Chapter 2 Page 195

That system has come gradually more and more into fashion. The Old Subsidy was imposed indifferently upon exportation as well as importation. The four subsequent subsidies, as well as the other duties which have been occasionally imposed upon particular sorts of goods have, with a few exceptions, been laid altogether upon importation. The greater part of the ancient duties which had been imposed upon the exportation of the goods of home produce and manufacture have either been lightened or taken away altogether. In most cases they have been taken away. Bounties have even been given upon the exportation of some of them. Drawbacks too, sometimes of the whole, and, in most cases, of a part of the duties which are paid upon the importation of foreign goods, have been granted upon their exportation.

Only half the duties