The Wealth of Nations by Part 1 Chapter 10 Page 132

employments of labour and stock, seems not to be much affected, as has already been observed, by the riches or poverty, the advancing, stationary, or declining state of the society. Such revolutions in the public welfare, though they affect the general rates both of wages and profit, must in the end affect them equally in all different employments. The proportion between them, therefore, must remain the same, and cannot well be altered, at least for any considerable time, by any such revolutions.