THE ANIMAL AS A MOTOR. 



51 



The horse, if of average weight and condition, should do 

 a day's work at the rate of about two thirds of a horse- 

 power unit, or 22,000 to 25,000 foot-pounds per minute 

 for the day. A powerful horse may give a full horse- 

 power, and any animal may do for a short time vastly 

 more than its average rate of work. A man rated at 

 from a sixth to a tenth horse-power can, for a minute or 

 two at a time, perform a full horse-power, or even more. 



The daily work of the animal, at its best, depends 

 upon its exact accommodation to most favorable con. 

 ditions for the development of the best work of the 

 individual, and upon its size, natural strength, endur- 

 ance, and spirit. These qualities in turn are dependent 

 upon the breed, the state of health, and the general 

 condition of the animal, its food, its environment, the 

 weather, the climate, and the adaptation of its load to 

 its habits and training. While at work the main ele- 

 ments of most effective operation are the load and the 

 speed adopted, at the time, and its distribution, day by 

 day and hour by hour. At maximum load the animal 

 does minimum work ; at maximum speed it can carry 

 no load ; at some intermediate load and speed it gives 

 maximum work, and this maximum varies with the time 

 of working, day by day. It is higher for short, lower 

 for long, working-days. For continuous work it is 

 usually assumed that eight hours a day, at one third 

 maximum speed and under one third maximum load, 

 gives highest results ; but this is true only under most 

 favorable conditions, with animals capable of doing a 

 full day's work, day by day, continuously without loss 

 of strength. In many cases four hours, and sometimes 

 even one, constitute a fair day's work. 



Animal power is most remarkably developed in the 



