FARM EXPERIENCE WITH THE TRACTOR. 5 



apparently not anticipated by those interested in its production. 

 On account of its failure to maintain this position the heavy demand 

 for gas tractors in those sections was only temporary, and an over- 

 supply of tractors was placed upon the market, resulting in depression 

 in the industry. Similar overproduction due to lack of foresight 

 has occurred in other lines of farm equipment, one of the best exam- 

 ples being the oversupply of grain harvesters during the period of 

 rapid multiplication of the improved models. 



Generally speaking, the farm tractor has thus far merely supple- 

 mented the work of the farm horse and relieved him of the heavier 

 work; it has not actually replaced horses to any considerable extent. 



TRACTOR RATINGS. 



When internal-combustion tractors were first introduced, there was 

 considerable confusion among engine users as to their ratings, owing 

 to the fact that several methods were used in computing and desig- 

 nating their horsepower. There are still several formulas used in 

 computing the power developed by the motor, but the terms by which 

 the power is denoted have become more uniform and more generally 

 understood. The terms "brake" or "belt" horsepower are used 

 to denote the total amount of power which the engine will develop 

 and transmit to a belt for stationary work, such as thrashing. This 

 amount of power may be computed or ascertained by actual meas- 

 urement with a proper apparatus. 



The "drawbar" horsepower is the belt horsepower minus the 

 amount of power required to propel the weight of the tractor. Most 

 tractors require approximately 50 per cent of the total power devel- 

 oped by the engine to move its own weight, leaving the remainder 

 available for pulling other implements. The amount of power 

 which is actually exerted on the drawbar varies, of course, with 

 the weight and construction of the tractor, and may be either com- 

 puted or measured with a dynamometer. The tractor ratings are 

 ordinarily expressed by writing the brake horsepower after the draw- 

 bar horsepower; thus, "30-60" would indicate a tractor having a 

 pull of 30 horsepower on the drawbar and developing 60 for stationary 

 work. 



The term "horsepower" denotes an amount of power equivalent to 

 that developed by a 1,500-pound horse moving at the rate of 2\ 

 miles per hour and exerting a pull equal to one-tenth of his own weight, 

 or 150 pounds. This represents a power output capable of raising a 

 weight of 33,000 pounds to a height of one foot in one minute, and 

 these figures are commonly used in computing the power developed 

 by an engine. A pull equal to one-tenth of his weight is considered 

 a normal load for a horse. As most farm horses weigh less than 

 1,500 pounds, it is apparent that they do not ordinarily furnish a 



