TT _ . f .1 -, lO.O-iU.UUU It/.-lU. 



Hence: Efficiency of the horse = Q0 1finnnn f . 1U = 0.19 or 19 



554 MACHINES, WORK, AND ENERGY 



Cal. of energy. But these 27,000 Cal.= 83,160,000 ft.-lb. of work 

 (Art. 654). 



Second: 1 horse-power for eight hours = 8 X 60 X 33,000 ft.-lb. 

 or 15,840,000 ft.-lb. of work. 



15,840,000 ft.-lb. 

 83,160,000 ft.-lb. 

 per cent. 



What is the cost of feeding this horse? We shall suppose that 

 oats are worth 40 cts. a bu. (32 lb.). The cost of 18 Ib. will be 

 223^ cts. If we count the cost of the 12 lb. of hay at $15 a ton, 

 we must add 9 cts. more making the cost for feed 31> ct. per day. 

 Thus we see that, considering the cost of feed and coal only, the horse 

 is some six or eight times as expensive as is the steam engine when 

 used as a motor. 



2. Work and Cost of Feed of an 1100-lb. Horse. Henry, in Feed 

 and Feeding, concludes that an 1100-lb. horse should be able to haul a 

 load 20 miles in a day, exerting an average pull of 100 lb. and that 

 the horse should walk at the rate of 2.9 miles an hour. How many 

 hours does he expect the horse to work? At how many horse-power 

 does he expect this horse to work? Ans. About 0.8 horse-power. 



Henry gives as the proper ration for this horse the following: 10 

 lb. of meadow hay; 10 lb. of oats and 6.4 lb. of corn. If the hay 

 costs $15 a ton, oats 40 cts. a bu., and corn 60 cts. a bu., what 

 is the cost of feeding this horse per day? 



How many foot-pounds of work does this horse do a day? 

 What is the cost of feeding this horse while he does 1 horse-power- 

 day (of eight hours) of work? Ans. About 33 cts. 



If the coal to run a steam engine costs 4 cts. per horse-power-day 

 (day = eight hours), how does the cost for feed of this horse compare 

 with the cost of coal to run the engine while the two motors are 

 doing the same amount of work? 



How do you think that the cost of care and shelter of such a horse 

 would compare with the cost of care and shelter for a 1 horse-power 

 steam engine? What is true about the cost of caring for a horse and 

 such an engine when they are not at work? How would the money 

 invested in the horse compare with that invested in a 1-horse-power 

 steam engine? Do you see why all these things must be considered 

 when comparing a horse with a steam engine as a motor? 



659. A Man can not Compete with Either the Horse or the 

 Steam Engine as a Motor. It is generally agreed that a 

 man of average strength can work at the rate of % to % of a 

 horse-power for eight hours a day. This means that it re- 



