The particular economic problems which are presented to each generation of our people are the resultant of all these factors taken together. A change in any one of them alters to some extent the nature of the problem. The problems change, for example, (a) with the discovery or the exhaustion (or the increase or decrease) of any kind of basic material resources; (b) with the multiplication or the improvement of tools and machinery or the invention of better industrial equipment; (c) with changes in the ideals, education, and capacities of any portion of the people whether or not due to changes in the race composition of the population; (d) with the increase or decrease of the total number of people, and the consequent shift in the relation of population to resources. Many examples of such changes may be found in American history, and some knowledge of them is necessary for an appreciation of the genesis and true relation of our present-day problems. § 4. #Attempts to summarize the nation's wealth.# If we seek to compare the material resources of the nation at one period in our history with those at another period, we find that it is impossible to find a single satisfactory expression for them. Let us examine the figures for the (so-called) "wealth of the people of the United States",[1] as it has been calculated by the census officials. Average total per capita Population. "wealth." wealth. 1850 23,200,000 $7,136,000,000[a] $308 1860 31,400,000 16,160,000,000[a] 514 1870 38,600,000 24,055,000,000[a b] 624 1880 50,200,000 43,642,000,000 870 1890 62,900,000 65,037,000,000 1,036 1900 76,000,000 88,517,000,000 1,165 1904 82,500,000 107,104,000,000 1,318 1912 95,400,000 187,739,000,000 1,965 [Footnote a: Taxable only; all other figures include exempt.] [Footnote b: Estimated on a gold basis.] A detailed comparison of the classes of concrete things making up the totals is possible only in the last three sets of figures (1900 to 1912), and they are here given (omitting 000,000).