[6]. One of the best things ever written is the chapter on “Habit” in William James’s Psychology. No one will regret the time spent in reading it.
[7]. The following table shows the increase, by decades, in round figures:
| 1790— 3,900,000 | 1840— 17,000,000 | 1890— 62,900,000 |
| 1800— 5,300,000 | 1850— 23,100,000 | 1900— 75,900,000 |
| 1810— 7,200,000 | 1860— 31,400,000 | 1910— 91,900,000 |
| 1820— 9,600,000 | 1870— 38,500,000 | 1920—105,000,000 |
| 1830— 12,800,000 | 1880— 50,000,000 |
From this it will be seen that the ratio of increase is declining. The population increased about one-third in each decade from 1790 to 1860; by about one-fourth in each decade from 1860 to 1890; by about one-fifth in the two decades from 1890 to 1910; and by less than one-sixth in the decade from 1910 to 1920.
[8]. It is customary to think of India and China as very densely populated; but both have fewer than 225 inhabitants to the square mile.
[9]. A map showing the progress of the center from East to West will be found facing this page.
[10]. Mr. H. G. Wells, in his interesting book entitled When the Sleeper Wakes, gives a picture of what the world will be like if all its inhabitants live in cities, and the country workers are carried back and forth by rapid transit.
[11]. In 1880, for example, only about four per cent of the immigrants were Italians while about thirty per cent were Germans; in 1910 the Italians had risen to more than twenty per cent while the German immigrants had declined to less than five per cent.
[12]. From 1783 to 1820 it is estimated that not more than 250,000 immigrants came to the United States. P. F. Hall, Immigration, p. 4. The total population in 1820 was ten millions.
[13]. The monotony of labor, however, is to some extent a matter of temperament. Some workers find even routine tasks interesting because they are constantly trying to attain greater expertness at the particular job. Others find work of a very varied character to be monotonous.