"Labor is the industrial exertion of a single man on some single piece of work, and on that single piece of work only, no matter what this may be—the carrying of a sack or the wheeling of a barrow, which requires no training at all; or the finishing of a chronometer, which requires the training of half a life-time. Ability is the industrial exertion of a single man, which affects simultaneously the labor of many men, multiplying or improving the results of it in each case."
(from "Who Are the Chief Wealth Producers" by W.H. Mallock. in The North American Review, June 1893, p.653)