The density of populations cannot be predicted for an extended period because the factors are so numerous and variable. Nevertheless, the changes are never abrupt and it has been possible in the past to make fairly accurate predictions for fifty years. Elkanah Watson made such a calculation in 1815, and his figures are quoted by Robert Hunter in his work on "Poverty," page 359, from the "Report of the Industrial Commission," Vol. XV, 1901. Unforeseen changes in civilization rendered these predictions wide of the mark after 1865.* In 1830 another estimate was made as to the conditions in 1880, and published in an almanac in 1833. I remember reading this in 1884, and was astounded at the accuracy of the prediction.

We can now calculate what the population will be in 1950, but later conditions are beyond our ken. Most of the predictions have ignored the fact that the percentage of increase lessens as the density increases. For instance, the population in 1900 would have been 100,000,000 if the rate of thirty-five per cent, per decade had continued after 1860, but that rate has been steadily diminishing until it is now somewhere in the neighborhood of sixteen. The safest plan, then, is to draw a curve of the percentage decennial increases and continue it into the future. From this curve we can calculate the total decennial increases and total population, and construct two more curves, which must not show abrupt changes of direction. Such a method gives us the following figures:

 *Year Population Watson's Estimate Foreign Immigration for the Decade 1790........... 3,929,214 ... .... 1800........... 5,308,483 ... 50,000 1810........... 7,239,881 .... 70,000 1820........... 9,633,822 9,625,734 114,000 1830........... 12,866,020 12,833,645 143,439 1840........... 17,069,453 17,116,526 599,125 1850.......... 23,191,876 23,185,368 1,713,251 1860........... 31,443.321 31,753,824 2,598,214 1870........... 38,558,371 42,328,432 2,314,824 1880........... 50,155,783 56,450,241 2,812,191 1890........... 62,622,250 77,266,989 5,246,613 1900........... 75,559,258 100,235,985 3,687,564
 Year Continental Population Decennial Increases Percentage Decennial Increases 1790............ 3,929,214 ... ... 1800............ 5,308,483 1,379,269 35.1 1810............ 7,239,881 1,931,398 36.4 1820............ 9,638,453 2,398,572 33.1 1830............ 12,866,020 3,227,567 33.5 1840............ 17,069,453 4,203,433 32.7 1850............ 23,191,876 6,122,423 35.9 1860.... 31,443,321 8,251,445 35.6 1870............ 38,558,371 7,115,050 * 22.6 1880............ 50,155,783 11,597,412 30.1 1890............ 62,947,714 12,466,467 24.9 1900............ 75,994,575 13,046,861 20.7 1905............ *82,567,998 ... ..... 1910............ 89,195,000 13,200,000 17.4 1920... 102,396,000 13,200,000 14.8 1930............ 115,300,000 12,900,000 12.6 1940............ 127,500,000 12,200,000 10.6 1950............ 138,850,000 11,347,000 8.9 1960............ 148,850,000 10,000,000 7.2 1970............ 157,600,000 8,780,000 5.9 1980............ 165,000,000 7,400,000 4.7 1990............ 171,000,000 6,000,000 3.6 2000............ 175,500,000 4,500,000 2.6

The following estimates of Mr. C. S. Shane, Geographer of the Census Bureau, have been kindly furnished me by Mr. W. S. Rossiter, the Acting Director:

* Partly estimated.

*  Probably defective.

 Year Bureau of the Census Method Decreasing Percentage of Increase 1910............................. 89,135,413 90,965,506 1920............................. 102,276,251 107,976,056 1930............................. 115,417,089 127,087,818 1940............................. 128,557,927 148,311,484 1950............................. 141,698,765 171,596,387 1960............................. 154,839,603 196,821,056 1970............................. 167,980,441 223,785,541 1980............................. 181,121,279 252,206,305 1990............................. 194,262,117 281,714,443 2000............................. 207,402,955 311,857,888

The Bureau method is the assumption that the increase each year will be one-tenth of the total increase of the previous decade. It is useless to estimate population as far ahead as 2000, for new factors may bring it to a standstill or even diminish it. Nevertheless, the practical agreement as to population in 1950 shows that we are now in a critical period when the additions to the population are diminishing. The decennial increase which was only 1,333,000 in 1790, and gradually mounted to 13,000,000 in 1900, will be 11,333,000 in 1950, and the decennial percentage increase will have dropped from thirty-five and one-tenth to seven and two-tenths. That is, the facts show that the phenomenal increases, due to the undersaturation of the country, are already a thing of the past. Indeed, Mr. Rossiter reports* that in 1905 some parts of the United States, Iowa, for instance, had actually less population than in 1900. In 1908 there was such a check to immigration and stimulus of emigration of the aliens that there were times when the outflow exceeded the inflow, and the net immigration increase for the year ending October 31, was only 6,298.

The State Censuses of 1905 have been studied by J. F.Crowell,*  and he has discovered a general tendency to arrest of population increase, with here and there remarkable decreases. He shows that it is a phenomenon in both agricultural and manufacturing communities, in none of which has the increase of five years been what was expected.

* The American Review of Reviews, July, 1906. *  Science, December 29, 1905.