218 POWER AND THE PLOW 



to each horse, the draft per foot of width would be 57.5 Ibs. 

 Professor Davidson, of Iowa, obtained a higher draft than this, a 

 single- disk drill with ten furrow openers, 8 inches apart, hav- 

 ing a draft of 68.6 Ibs. per foot of width. Drills usually place 

 the seed about 2 inches below the surface; consequently the 

 work of drilling and covering seed takes approximately the 

 same power per acre-inch as the disk or drag harrows doing 

 work as shown in the table. 



Mowing machines are usually operated with two horses for 

 a 5 or 6 foot cut, indicating a draft of about 300 Ibs. A leading 

 manufacturer places the draft from 190 to 325 Ibs. for a 

 5-foot mower. Two other authorities place the draft at from 

 285 to 340 Ibs. for the same width. The draft may easily be 

 doubled by dull knives, tight boxes, or too low speed. The 

 knives are not serrated as in the case of the binder; hence about 

 three times the speed of cutter bar must be maintained in 

 order to cut cleanly through the tough stems of forage grasses. 

 The 6-foot mower will of course require more power than the 

 5-foot, but not in proportion to the extra cut. In one test, 

 five mowers run in gear but not cutting showed an average 

 draft of 154 Ibs. While cutting the average was 268 Ibs., show- 

 ing that 57^ per cent, of the draft was due to the running of the 

 machine. The actual work of cutting apparently consumed 

 about 23 Ibs. per foot. In an actual test of a 4i-foot and a 

 6-foot mower of the same make the drafts were 203 Ibs. and 

 263 Ibs., respectively. This shows about 34 Ibs. of draft for 

 each added foot cut. However, the extra weight of frame and 

 the added size of bearings increased the draft somewhat. It 

 is evident that the wide cut mowers are economical in the same 

 way that the engine is economical when running at high per- 

 centage of its rating, less being wasted in internal friction. 



The kind of grass cut and the thickness of stand have an 

 important bearing on draft, but, owing to different speeds of 

 cutter bar, different mowers show lighter draft in different 

 grasses. In an experiment by Sanborn, in which five mowers 



