SOURCES OF POWER FOR PLOWING 13 



face unevenly, and sets up air currents, which drive our wind- 

 mills. It lifts water from the sea and drops it on the mountain 

 tops. On its course back to the ocean the stream drives the 

 water-wheel. The newly invented solar motor derives its 

 power from the sun's rays, which it intercepts directly. Man 

 and the draft horse obtain their power through assimilating 

 the energy which the sun stores up each year in plants. Even 

 the feeble wave motors are agitated by forces of which the 

 sun is the centre. 



In the ordinary classification the electric motor is included, 

 but it is not, strictly speaking, a prime mover, since it merely 

 transforms into mechanical energy the electric current which 

 has been derived from another source. The windmill, the 

 water-wheel, and the wave motor intercept the motion of air 

 or water in the mass and may be called gravity, or kinetic 

 motors. The heat engines, by supplying the conditions for 

 the oxidation of fuel, convert it into heat, thence into work. 

 They derive power from the chemical changes that are produced 

 and have been called chemical motors. These are by far the 

 most important with which we have to deal. Possibly the most 

 stupendous discovery in the history of the world was that the 

 heat from burning materials could be made to do the work of 

 men and animals. 



It is our intention to devote space only to those motors used 

 for plowing, hence we shall pass over wind, wave, water, solar, 

 and hot air motors with a mere mention and discuss the electric 

 motor briefly, in its proper order. The world over, the animal 

 is most common motor for plowing. Human labor is still put 

 to this wasteful use in a few countries, including even Japan 

 and modern Switzerland. In all countries, however, which 

 are not so densely populated as to make live stock raising 

 practically out of the question, the inhabitants have substituted 

 brute labor for human muscle. The picturesque water buffalo 

 is the common beast of burden in the Phillipines, both for 

 agriculture and transportation. In the land of the Pharaohs 



