7. The nature of income. (King, Wealth and Income of the People of the United States, chapter v.)
8. Relation of public education to income. (Thompson, Elementary Economics, pages 299-303.)
9. Reasons for the scarcity of capital. (Carver, Elementary Economics, chapter xxxvi.)
10. The productivity of capital. (Taussig, Principles of Economics, vol. ii, chapter xxxviii.)
11. Historical changes in the rate of interest. (Bullock, Selected Readings in Economics, pages 563-568.)
12. The rent of land. (Carver, Elementary Economics, chapter xxxiii.)
13. Causes of the scarcity of labor. (Carver, Elementary Economics, pages 270-271.)
14. Historical changes in the rate of wages. (Bullock, Selected Readings in Economics, pages 533-543.)
15. The nature of profits. (Carver, Elementary Economics, chapter xxxvi.)
16. Relation of profits to risk. (Taussig, Principles of Economics, vol. ii, chapter xlix, section 1.)