The actual opposition of the masters to the mental improvement of Negroes, however, did not assume sufficiently large proportions to prevent the intellectual progress of that race, until two forces then at work had had time to become effective in arousing southern planters to the realization of what a danger enlightened colored men would be to the institution of slavery. These forces were the industrial revolution and the development of an insurrectionary spirit among slaves, accelerated by the rapid spreading of the abolition agitation. The industrial revolution was effected by the multiplication of mechanical appliances for spinning and weaving which so influenced the institution of slavery as seemingly to doom the Negroes to heathenism. These inventions were the spinning jenny, the steam engine, the power loom, the wool-combing machine, and the cotton gin. They augmented the output of spinning mills, and in cheapening cloth, increased the demand by bringing it within the reach of the poor. The result was that a revolution was brought about not only in Europe, but also in the United States to which the world looked for this larger supply of cotton fiber.[1] This demand led to the extension of the plantation system on a larger scale. It was unfortunate, however, that many of the planters thus enriched, believed that the slightest amount of education, merely teaching slaves to read, impaired their value because it instantly destroyed their contentedness. Since they did not contemplate changing their condition, it was surely doing them an ill service to destroy their acquiescence in it. This revolution then had brought it to pass that slaves who were, during the eighteenth century advertised as valuable on account of having been enlightened, were in the nineteenth century considered more dangerous than useful. [Footnote 1: Turner, _The Rise of the New West_, pp. 45, 46, 47, 48, and 49; and Hammond, _Cotton Industry_, chaps. i. and ii.]