354 A Manual of Veterinary Physiology. 



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 621 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 

 1,<S40 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. lifted 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 :\\ hours per 

 diem, whereas his most useful work is performed in S hours. 



