In Prussia, by laws enacted in the years 1688, 1721, 1726 and 1736, and by various government measures, endeavors were made to encourage immigration; especially were the immigrants welcomed who had been subjected to religious persecution in France and Austria. The theories in regard to population maintained by Frederick the Great were expressed with brutal frankness in a letter written by him to Voltaire on the 26th of August 1741. He wrote: “I consider men as a herd of deer in the deer park of some great lord, having no other task but to populate the park.” By his wars he certainly made it necessary to have his deer park repopulated. In Austria, Wurtemberg and Brunswick immigration was also encouraged and there, as in Prussia, emigration was forbidden. Furthermore, in the course of the eighteenth century, England and France removed all obstacles to marriage and settlement, and other nations followed their example. During three-fourths of the eighteenth century political economists as well as the governments considered a large population the greatest good fortune to the state. Only at the close of the eighteenth and the beginning of the nineteenth century a reversion of opinion took place. This was due to economic crises and to warlike and revolutionary events, that continued during the first half of the nineteenth century, especially in Germany and Austria. The age at which marriage was permitted was raised again, and proofs were required showing that the contracting parties were assured of a certain amount of wealth or a secure income, and could maintain a given standard of living. To the destitute, marriage was made impossible, and the municipalities were given a great influence in determining under what conditions marriages might be contracted. Occasionally peasants were even forbidden to build their little homes, or compelled to tear them down when they had been built without princely permission. Only in Prussia and Saxony the marriage laws remained comparatively liberal. Since human nature will not be suppressed, the result of all these hindrances to marriage was, that in spite of all the harassing and persecution, illicit relations greatly increased, and that in some German states the number of illegal children was almost as great as that of the legal ones. Such was the fruit of a paternal government that prided itself on its Christian morality. 3.--The French Revolution and the Rise of Industry.