more than those of another. Desaguliers's measure is, that a horse will walk at the rate of 21⁄2 miles per hour, against a resistance of 200lbs,* and which gives, as a number for comparisons, 44000; that is, the raising of 1lb. 44000 feet in a minute; or, what amounts to the same, the raising of 44000lbs. 1 foot in a minute. Emerson's measure is the same as Desaguliers's, (see Emerson's Mechanics, p. 178,) and Mr. Smeaton's result is 22916lbs. under the same circumstances.† Mr. Watt has found, from repeated experiments, that 33000lbs. 1 foot per mi * When working 8 hours a day, (Desaguliers's Course of Experimental Philosophy, Vol. I. p. 241.) 24 miles per hour is equal to 220 feet per minute, or 33 feet per second. (Ed.) + Reports, Vol. I. p. 229. But Desaguliers gives the immediate power of a horse, Smeaton the effect of that power applied to raise water: hence the friction of the machinery should be added to Smeaton's horse's power. (Ed.) nute, was the average value of a horse's power; but, I believe that his engines were calculated to work equal to 44000lbs. 1 foot per minute. But, that he allows only 33000 in his calculations, applied to mills, considering the difference as being lost in the friction of the engine itself. 80. It is common in practice, to reckon, that it requires one horse's power to drive 100 spindles with preparation of cotton water twist. 81. 1000 spindles with preparation cotton mule yarn. 82. 75 spindles with preparation flax yarn. I beg leave here to make the following extract, on the subject of animal force, from Dr. Young's Natural Philosophy, Vol. II. p. 165. 83. "In order to compare the different estimates of the force of moving powers, it will be convenient to take a unit which may be considered as the mean effect of the labour of an active man, working to the greatest possible advantage, and without impediment; this will be found, upon a moderate estimation, sufficient to raise 10 pounds 10 feet in a second, for 10 hours in a day; or to raise 100 pounds, which is the weight of 12 wine gallons of water, 1 foot in a second, or 36000 feet in a day, or 3,600,000 pounds, or 432000 gallons, 1 foot in a day; this we may call a force of 1, continued 36000". [A. 85.] The power of men and horses to move machines, has very frequently been made a subject of investigation by writers on mechanics; but yet it appears possible to consider it in a different manner, which will furnish results from principles somewhat more strictly practical than those which have hitherto been made the basis of calculation. 1. It is almost always a necessary con * Vol. I. p. 229. |