6 
BULLETIN 1348, U. S. DEPAETMEKT OF AGEICULTUEE 
a nmnber of sources it has not always been practicable to name each 
individual source. 
Much of the statistical information presented is based on data 
obtained from publications of the Bureau of the Census, United 
States Department of Commerce, and the Bureau of Agricultm-al 
Economics, United States Department of Agriculture. Such statis- 
tics may be considered as fairly accurate; but the figures for the 
power requirements of farm operations, those representing the pro- 
duction of various farm commodities, and those for the total amount 
of power utilized have been based on rather lunited data and must be 
considered as only approximately correct, since so many factors enter 
into their determination that much more experimental information 
1920 1924 
FiG. 5. — Estimated total primary horsepower available on farms of United States from 
1850 to 1924 inclusive 
will be necessary before they can be determined accurately for all con- 
ditions. The immediate need for information of this kind, however, 
in order to give some comprehension of the nature of the farm- 
power problem, justifies the publication of the available data. 
SOURCES OF POWER USED ON FARMS 
The sources of power now available on farms in the United States 
in addition to human labor are animals, gas engines (including 
tractors, trucks, and automobiles) , steam engines, ajid electric, wind, 
and water motors. 
The power of animals was the earliest form of power to be utilized 
by man, and up to about 60 years ago this som'ce afforded prac- 
tically the only power used by agriculture in the United States. 
Wind had been used to some extent, but the areas where windmills 
are most efficient were not settled before 1860; stationary steam en- 
