By the 'mud-sill' theory it is assumed that labor and education are incompatible; and any practical combination of them impossible. According to that theory, a blind horse upon a tread-mill, is a perfect illustration of what a laborer should be -- all the better for being blind, that he could not tread out of place, or kick understandingly. According to that theory, the education of laborers, is not only useless, but pernicious, and dangerous. In fact, it is, in some sort, deemed a misfortune that laborers should have heads at all.