140 SCIENCE OF SUCCESSFUL THRESHING 



those in the bull-pinions and inside-pinions are cut with 

 reference to one of their teeth so that when the pinions are 

 keyed to the shaft, their teeth will be in line. It will be 

 seen that if the shaft has been twisted so that the teeth of 

 the pinions are even slightly out of line, the power cannot 

 be made to run properly. A new spur-wheel shaft is the 

 only remedy for such a condition. 



Work Done by Horses. The sweeps of the twelve- 

 horse-power and smaller sizes are twelve feet and seven 

 inches long, and their ends move in a circle the circumfer- 

 ence of which is seventy-nine feet. The sweeps of the 

 fourteen-horse power are fourteen feet long, and their ends 

 move in a circle, the circumference of which is eighty-nine 

 feet. Horses ordinarily travel around the seventy-nine 

 foot circle two and one-half times a minute, and around the 

 eighty-nine foot circle two and one-fourth times a minute, 

 in either case covering about two and one-fourth miles per 

 hour. The term "horse-power" (the standard measure of 

 power) is defined as the power necessary to raise 33,000 

 pounds one foot per minute. A horse walks two hundred 

 feet per minute in traveling around the eighty-nine foot 

 circle two and one-quarter times per minute so that to do 

 work equal to one "horse-power" it is necessary for it to 

 pull only one hundred and sixty-five pounds, which is the 

 quotient of 33,000 divided by 200. This quotient does 

 not allow for the friction of the machine. As the efficiency 



