It is sometimes attained by engines of the Watt type, but very rarely surpassed. This latter product amounts, in French measures, to 104,000 kilograms raised one metre per kilogram of coal consumed.
According to what is generally understood by one horse-power, in estimating the duty of steam-engines, an engine of ten horse-power should raise per second 10 × 75 kilograms, or 750 kilograms, to a height of one metre, or more, per hour; 750 × 3600 = 2,700,000 kilograms to one metre. If we suppose that each kilogram of coal raised to this height 104,000 kilograms, it will be necessary, in order to ascertain how much coal is burnt in one hour by our ten-horse-power engine, to divide 2,700,000 by 104,000, which gives = 26 kilograms. Now it is seldom that a ten-horse-power engine consumes less than 26 kilograms of coal per hour.
