60 



beast of burden. The amount of such muscular work has been calcu- 

 lated or measured in various ways. The methods of calculation are 

 often complex and need not be discussed in detail. The amount of 

 muscular work performed has usually been measured with some form 

 of dynamometer. An extended series of experiments in which such an 

 instrument was employed was conducted by Wolff. " The dynamometer 

 which he used consisted of a revolving arm, turning on a base, which 

 could be weighted so as to increase the friction and hence the amount 

 of work required to turn it. There were special devices for recording 

 the number of revolutions made. 



According to the classic experiments of James Watts, a horse can 

 exert a power equal to 33,000 foot-pounds per minute, i. e. , in 1 minute 

 can exert a force sufficient to raise 33,000 pounds 1 foot. This value 

 has been termed 1 -horse power and has been accepted as a common 

 unit for the measurement of force. In countries where the metric 

 system is employed the more common unit is the kilogrammeter. 

 This unit is equal to 7.3 foot-pounds. According to Watts's values, a 

 horse working eight hours per day would perform work represented 

 by 33,000 X 60 X 8 = 15,8-10,000 foot-pounds. Later estimates give 

 lower values. It has been calculated that an average horse will pro- 

 duce only about 22,000 foot-pounds per minute, which would be 

 equivalent to 10,560,000 foot-pounds in a working day of eight hours. 



According to Wolff's experiments/' the day's work of a horse haul- 

 ing a load eight hours on a level road amounted to T,l>99,800 foot- 

 pounds. Working the same length of time with a dynamometer the 

 work amounted to 12,996,000 foot-pounds. As will be seen by the 

 figures given below^ (p. 61), Lavalard obtained larger values in his 

 calculations representing the amount of work performed daily by 

 army horses. 



Mention should be made in this connection of some comparatively 

 recent investigations carried on at the American experiment stations 

 and other institutions. At the Utah, New York (Cornell), Michigan, 

 and Missouri stations and at the University of Tennessee, Sanborn, 

 Roberts, Fulton, Waters, and Carson have studied the draft of differ- 

 ent kinds of wagons under different road conditions and related topics, 

 thus securing data for estimating the work done by horses under the 

 conditions studied although the experiments were not made from this 

 standpoint. A number of the experiment stations have also devoted 

 considerable attention to testing the draft of plows and other agricul- 

 tural implements. 



« For full accounts of the extended experiments of Wolff and his associates con- 

 cerning the digestibility of different feeds, the i^roduction of muscular work, etc., 

 see Landw. Vers. Stat., 20 (1876-77), p. 125; 21 (1877-78), p. 19. Landw. Jahrb., 

 8 (1879), Sup. 1; 13 (1884), p. 257; 16 (1887), Sup. Ill; 24 (1895), p. 125; also 

 Grundlagen fiir die rationelle Fiitterung des Pferdes, Berlin, 1885. 



