THE HORSE AS A MOTOR 31 



various writers, including authorities of the United States 

 Department of Agriculture, the real thermal efficiency of an 

 average horse, even at heavy, continuous work, is probably 

 not more than 6 to 10 per cent. Many internal combustion 

 tractors have done as well as this in draft tests, and some 

 much better. 



Under laboratory conditions, with scientifically fed animals 

 doing maximum work, a thermodynamic efficiency of 20 per 

 cent, has been obtained, that is, one pound of food has been 

 turned into work for every four wasted. Farm conditions, how- 

 ever, and even teaming conditions in cities, are vastly different 

 from those of the laboratory. 



