AN" APPRAISAL OP POWER USED 0:N" FARMS 5 
and less expensive types of power units and by a more extensive use 
of power to replace expensive human labor. 
This bulletin is a summary of the information now available that 
has to do with the use of power in agriculture, and is intended to 
serve as a basis for further research toward more efficient power 
utilization by the agricultural industry. 
Fig. 4.— Estimated horsepower-hours of power developed annually by different kinds of power used 
on farms and the amounts required for the principal farm operations in the United States 
SOURCES OF INFORMATION 
Material from all sources available has been drawn upon freely. 
A selected bibliography of the pubhcations used is given in Appen- 
dix II. In addition much valuable material was obtained directly 
from the Bureau of Agricultural Economics, United States Depart- 
ment of Agriculture, the various State colleges and State agricultural 
statisticians, the Federal Power Commission, the Interstate Commerce 
Commission, manufacturers of agricultural equipment, farm pubh- 
cations, and individuals interested in the i arm-power problems. 
Where material is quoted directly credit has been given; but in many 
cases where tables have been based upon information obtained from 
