The Wealth of Nations by Part 5 Chapter 2 Page 127

maid-servants are taxes, not upon stock, but upon expense, and so far resemble the taxes upon consumable commodities. The tax of a guinea a head for every man-servant which has lately been imposed in Great Britain is of the same kind. It falls heaviest upon the middling rank. A man of two hundred a year may keep a single manservant. A man of ten thousand a year will not keep fifty. It does not affect the poor.

Taxes upon the profits of stock in particular employments can never affect the interest of money.

Nobody will lend his money for less interest to those who exercise the taxed than to those who exercise the untaxed employments. Taxes upon the revenue arising from stock in all employments where the government attempts to levy them with any degree of exactness, will, in many cases,