Practical Questions in Plows and Plowing. 163 



imiiiher of experiments shall have been carefnlly made we may 

 ascertain the law nearly enongh for all practical pnrposes. The 

 average increase of draught per inch in Mr. Pusey's experiments 

 was 12.29 per cent. In Mr. Morton's experiments it was 9.62 per 

 cent, and in our own experiments it was 5.38 per cent. The 

 average of all these is 9.09, say in round numbers, ten per cent 

 of increase in draught for each additional inch depth of furrow 

 between the limits of four and twelve inches. 



If this conclusion approximates to correctness it appears that 

 the draught increases in proportion to the depth much less rap- 

 idly than has been heretofore supposed. Mr. Pusey says that it 

 has been laid down in our books that the draught increases as the 

 squares of the depth; that is to say, that if the draught at four 

 inches be 252 pounds, at seven inches it will be as 49 to 16, or 

 756 pounds, whereas experiment shows that on an average it is 

 only 308 pounds, or less than half that amount. 



It must not be forgotten that both theory and experiment show 

 that plows made expressly for deep tillage will work relatively 

 lighter in a deep furrow than in a shallow one. Thus a plow 

 made expressly for a four inch furrow compared Avith one made 

 for a twelve inch furrow Avill work in the furrow it was desio-ned 

 for with much less draught than a deep plow; but if the four 

 inch plow is made to take a furrow ten inches deep, the plow 

 designed for twelve inches will be found to require much less 

 draught. This fact should never be lost sight of in trials of this 

 kind. 



We know of no experiments made with a view to determine 

 the ratio of power required to turn over furrow slices of difi'er- 

 ent breadths while the depth remains uniform. 



There is another point upon which Mr. Pusey's experiments 

 throw much light, and which led to conclusions very different 

 from those which have been generally entertained. It has been 

 generally supposed that the power required to draw a plow 

 increased as the square of the velocity, but experiments show that 

 this is not the case. 



Mr. Pusey made repeated trials in order to settle this point 

 under a great variety of circumstances. The first trial was in the 

 moory ground mentioned in preceding tables, and with Clark's 

 plow. The horses were made to walk as slowly as possible, and 

 the draught was found to be 336 pounds in a five inch furrow. 

 The horses were now urged forward at their highest rate of speed, 



