The Wealth of Nations by Part 4 Chapter 7 Page 130

it naturally would have been in the case of a free trade. But, by lessening the competition of capitals in that branch of trade, it necessarily raised the rate of profit in that branch. By lessening, too, the competition of British capitals in all other branches of trade, it necessarily raised the rate of British profit in all those other branches. Whatever may have been, at any particular period, since the establishment of the Act of Navigation, the state or extent of the mercantile capital of Great Britain, the monopoly of the colony trade must, during the continuance of that state, have raised the ordinary rate of British profit higher than it otherwise would have been both in that and in all the other branches of British trade.

If, since the establishment of the Act of Navigation, the ordinary rate of British profit