All moneys derived from the sale of lands as provided in section 302 of this title by the States to which lands are apportioned and from the sales of land scrip provided for in said section shall be invested in bonds of the United States or of the States or some other safe bonds; or the same may be invested by the States having no State bonds, in any manner after the legislatures of such States shall have assented thereto and engaged that such funds shall yield a fair and reasonable rate of return, to be fixed by the State legislatures, and that the principal thereof shall forever remain unimpaired: Provided, That the moneys so invested or loaned shall constitute a perpetual fund, the capital of which shall remain forever undiminished (except so far as may be provided in section 305 of this title), and the interest of which shall be inviolably appropriated, by each State which may take and claim the benefit of this subchapter, to the endowment, support, and maintenance of at least one college where the leading object shall be, without excluding other scientific and classical studies and including military tactics, to teach such branches of learning as are related to agriculture and the mechanic arts, in such manner as the legislatures of the States may respectively prescribe, in order to promote the liberal and practical education of the industrial classes in the several pursuits and professions in life.