Licence: Public Domain Mark
Credit: A manual of veterinary physiology / by F. Smith. Source: Wellcome Collection.
Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.
374/440 page 354
![forward. As the resistance yields, the feet are carried for- ward, and the action continued.' Such is the theory of draught. The nature of the vehicle, the condition of the roads, the angle the trace forms with the horizontal, the presence or absence of springs, four wheels or two, high or low front wheels, and the width of the track, so complicate the question as to take it at once into the domain of pure mechanics, into which we cannot follow it. In the light or mail stage-coach, where 10 and 11 miles an hour were attained, the strain or force of traction em- ployed by each horse was only 40 lbs.; in the heavy coach it was 62] lbs. for each horse. For slow draught work at 2^ to 3 miles per hour, and for 8 hours a day (which appears to be the most suitable pace and duration of labour), a force of traction of from 100 lbs. to 125 lbs., or 150 lbs., is quoted by Youatt as being the most suitable. I have previously stated (p. 351) that I consider it probable that a force of traction of 120 lbs. for 8 hours a day is too much to expect from a horse. The higher the velocity the less the force of traction which can be employed, and the shorter the duration of labour. It has been stated (Landois) that a horse can only drag three times his own weight, and taking as a matter of con- venience his weight at 1,000 lbs., it is probable that 3,000 lbs. is the limit of his strength if tested against a dynamometer. Yet this amount is far above what it is usual to regard as the power of a horse. I have been credibly informed that a big railway horse could only exercise l,cS4'0 lbs. when tested against the dynamometer. The limit of a horse's power is therefore a very doubtful point. Watt found that a horse could raise a weight of 150 lbs. passed over a pulley, 220 feet per minute ; this, as applied to engines, is termed 'horse power,' and is equal to 33,000 lbs. HfteJ 1 foot high per minute, viz., 33,000 foot- pounds per minute. This standard of comparison cannot be applied to animal labour, as it is much too high. A horse could only perform this amount for 3i hours per diem, whereas his most useful work is performed in 8 hours.](https://iiif.wellcomecollection.org/image/b21933480_0374.jp2/full/800%2C/0/default.jpg)
