288 Feeds and Feeding. 



If tlie speed be increased beyond this, tlien less of the energy 

 can be devoted to drawing the load. With a speed of ten miles 

 per hour about two-tenths of the maximum work can be per- 

 formed, and a further increase of a mile and a quarter per hour re- 

 duces the possible work to less than one- tenth of the maximum. 



"■ Where the animal must develop maximum power continuously 

 at any considerable speed, the number required for a specific 

 work will always be greatly increased. Thus, in coaching, the 

 proprietors of mail-coaches, even on the admirable highways of 

 Great Britain^ maintain one horse per mile of route for each 

 coach and worked in fours, so that, going and retuining, each 

 travels eight miles per day, working only an hour or less each 

 day on the average. The coach weighs, loaded, two tons, and 

 its coefficient of friction on good roads is about .035." 



Draft horses moving two and one-half miles an hour are ex- 

 pected to do seven times the work of coach horses moving ten 

 miles. ^ 



450. Work done by the horse and the mule. — Eennie^ found 

 the hauling power of a draft horse weighing 1,200 pounds 

 equal to about 108 pounds at 2.5 miles an hour, or 22,300 foot- 

 pounds per minute, for 8 hours per day — a twenty-mile haul. 

 This is a little over two-thirds of a Watt horse-power, at which 

 value Rennie rates the average draft horse, and this is taken 

 to be, ordinarily, five times the power of a man. Between 2.5 

 and 4 miles an hour, the hauling power of the horse is nearly 

 inversely as the speed. 



The mule carries a load of 200 to 400 pounds, and its day's 

 work consists, usually, in the transportation of the equivalent of 

 5,000 to 6,000 pounds one mile. The ass carries 175 pounds and 

 upward, and its day's work is the equivalent of 3,000 to 4,000 

 pounds one mile. 



According to Weisbach, a horse should be able to carry 240 

 pounds on its back 3.5 feet per second ten hours a day. Carrying 

 160 poimds he should be able to trot seven feet per second seven 

 hours a day, doing in the day nearly ten per cent, less work than 

 before. 



^ Barbour, Cyclopaedia of Manufactures. 



« Thurston, The Anima l as a Machine and a Prime Motor, p. 59. 



