Thus, if one commodity has risen 4 per cent. since last month and another, 10 per cent., the average rise of the two is midway between the sum of 4 per cent., and 10 per cent., or 7 per cent. It is 4 + 10 ------ = 7 2 If we call the price level of the two articles last month 100 per cent., then 107 per cent. is the "index number" for the prices of the two articles this month. The same principle, of course, applies to any number of commodities. The index number of the United States Bureau of Labor Statistics, the best index number we have, shows an average price level in 1918 of 196 for wholesale prices and 168 for retail prices of food on the basis of 100 per cent. for 1913, the year before the war; showing that wholesale prices, on the average, almost exactly doubled. The latest index number for wholesale prices (May, 1919) is 206, and for retail (July, 1919), 190. A look at the history of prices shows the interesting fact that, while prices have sometimes fallen, they have generally risen. The high cost of living has been for centuries a source of complaint. In the 16th century, people objected to the price of wheat, which was three to ten times what it cost during the preceding 300 years. WORTHLESS PAPER MONEY Where, through ignorance of monetary science, irredeemable paper money was used, prices have sometimes gone up quite "out of sight." This was the case with the famous assignats of the French Revolution, and the "Continental" paper money of our own Revolution. After the Revolution a barber in Philadelphia is said to have covered the walls of his shop with continental paper money, calling it the cheapest wallpaper he could get! Jokes were also heard of a housewife taking a market-basket full of this "money" to the butcher's shop and bringing home the meat in her purse! This money became a hissing and a byword; and, even to this day, one of the favorite expressions for worthlessness is "not worth a Continental." We see the same situation repeated again today with Russian paper money. But our first scientific measurement of price movements began with 1782, the beginning of Jevons' index number of wholesale prices in England. COMMENTS ON FIGURE 1 Figure 1 shows the course of prices in England from that date, and also, for comparison, that in the U.S. [Illustration: Figure 1 Price Movements of the United States and England from the Earliest Index Numbers Through the First Years of the World War Showing, in general, a close similarity. England was on a paper basis, 1801--1820; and the United States, 1862--78. The dotted lines for these periods show the prices as translated back into gold.]