There was a time, before we had harnessed the powers of Nature to found, forge, spin, weave, print, and drudge for us generally, that in every civilized country the strong-headed men used their strong-handed brethren as machines. Only he could be very knowing who owned many scribes, or he very rich who owned many hewers of wood and drawers of water. With our prodigious development of mechanical inventions, iron and coal, our mighty steam-driven machinery for making machines, the time for chattelizing men, or depending mainly on animal power of any sort for the production of wealth, has passed by. Abrogate the golden rule, if you will, and establish the creed of caste,--let the strongest of human races have full license to enslave the weakest, and let it have the pick of soil and staples,-- still, if you do not abolish the ground rules of arithmetic, and the fact that a pound of carbon costs less than a pound of corn, and must cost less for at least a thousand years to come, chattelism of man will cease in another generation, and the next century will not dawn on a human slave. At present, a pound of carbon does not cost so much as a pound of corn in any part of the United States, and in no place visited by steam-transportation does it cost one fifth as much. We are already able to get as much work out of a pound of carbon as can be got from a pound of corn fed to the faithfullest slave in the world. Mr. Joule has shown us that there is really in a pound of carbon more than twice as much work as there is in a pound of corn. The human corn-consuming machine comes nearer getting the whole mechanical duty or equivalent out of his fuel than our present steam-engine does, but the former is all he ever will be, while the latter is an infant and growing. We shall doubtless soon see engines that will get the work of two slaves out of the coal that just balances one slave's food in the scales. Our iron-boned, coal-eating slave, with the advantage of that peculiar and almost infinitely applicable mechanical element, the wheel, may be made to go anywhere and do any sort of work, and, as we have seen, he will do it for one tenth of the cost of any brute or human slave.