66 FARM MACHINERY 



rows interfere with the carrying of water upon the land, 

 reversible plows are used. These are of many forms, but 

 the type will not be further discussed. 



99. The subsoil plow. Where it is desirable to loosen 

 the pn-mr^l to q g^ptfir Hppth jj^aji can be done with a 

 surface plow, the subsoil plow is used. It is used with 



FIG. 45 A SUBSOIL PLOW FOR LOOSENING THE SOIL IN THE BOTTOM OF 

 THE FURROW MADE BY THE COMMON PLOW 



the regular plow, following in the furrow made by it. 

 Opinions in regard to the value of this plow differ, but 

 the subject will not be discussed here. 

 x 100. The disk plow. The disk plow is the result of an 

 \VJreffort on the part of inventors to reduce the draft due to 

 M the sliding friction upon the moldboard. Figs. 46 and 47 

 show the modern disk plow made for horse and engine 

 power, respectively. A plow consisting of three disks 

 , cutting very narrow strips was about the first one patr_ 

 II ented, M. A. and I. N. Cravath, of Bloomington, Illinois, 

 being its inventors. Under certain conditions, it is saul, 

 WMthis plow did very satisfactory work, but the side 

 pressure was not sufficiently provided for. M. F. Han- 

 cock succeeded in introducing the disk plow into localities 



