power, as a mechanical mover, advantage is lost with every increase of speed beyond a very moderate limit; and that at certain rates, and those not high in degree, all useful effects disappear.
It is found in practice, that a waggon used on a turnpike road, and loaded to the amount of eight tons, may be drawn by horses, at the rate of two miles and a half an hour,—the horses working for eight hours daily. Thus the performance of a horse in this way will amount to one ton transported twenty miles a-day. A mail-coach, weighing two tons, and travelling at the rate of ten miles an hour, may be worked on a line of road in both directions by a number of horses equal to the number of miles. Thus, the performance of each horse would amount to two tons carried two miles daily, or four tons carried one mile. In the case, however, of horses working in this way, it appears, by a petition of coach proprietors presented to the House of Commons, that it is necessary to renew the stock every third year; from whence we must infer that the animal is overworked.
From what has been explained, respecting the resistance of fluids, and from the relation which I have shown to subsist between the speed of horses and the performances which they are able to effect, it will be apparent that that rate of motion which renders the resistance of a fluid least injurious to the effect produced, is also that speed at which a horse can work with the greatest possible effect. This speed is from two and a half to three miles an hour; and I accordingly find, that when horse power is used to propel a boat on a canal, the effect is a maximum at that rate of motion; but if a higher rate be attempted. I find, as might be easily anticipated from the principles already laid down, that the diminution of effect takes
