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 2h 
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 
