Thought some of y'all might find a passage out of an old textbook I picked up a few years ago. The book is "The American Government" by Frederic J. Haskin, published in 1923.

"The income tax to-day is the chief source of revenue. Approximately 7,000,000 individual returns are filed annually, not all of which, however, are taxable by reasons of the exemptions and credits. The intent of the tax law is that each person shall pay in proportion to his income. The man of moderate means pays only a normal tax, which, under the act of 1921, was 4 percent on the first $4,000 of net income above his exemptions and credits, and 8 per cent on the remaining net income. The man of larger means pays, in addition to the normal tax, a surtax, the rates ranging under the 1921 act from 1 per cent on the amount of the net income between $6,000 and $10,000 to 50 per cent on the amount in excess of $200,000."