Ploughs and Ploughing. 



295 



out ; but the modern one is a plate of chilled steel, the surface 

 of which is as slippery as a sheet of ice, the difference in the 

 draught, i.e., in the friction, between the old and the new being 

 something enormous. It is alleged that the particular brand 

 of chilled cast steel of which these are made can only be pro- 

 duced in the anthracite regions of America, and that those of 

 our home makers who try to imitate this style of make have 

 to import their wrests ready made — as they cannot be made 

 here — and fit them on to their own frames. 



These steel breasts are made of two sheets put together, the 

 outer one of the hardest chilled steel and the inner one of the 

 mild and tough variety, the inner tough coating preventing 

 the brittle outer skin from breaking. 



The shape and comparative size of the mouldboard is a 

 matter of great importance. In old times it was made as long 

 as possible. The idea was to cut and turn over the furrow-slice 

 gently, almost without cracking it, the resistance from friction 

 being less on a long than on a short mouldboard set to the 

 same width. As many men and some text-books have upheld 

 the contrary of this latter statement, it is here necessary to 

 make a digression to explain the laws of friction and of motion 

 up an inclined plane as applied to a plough. The " body " of 

 the plough, i.e., the share, wrest, sole, cheek-plate, &c, forms a 

 wedge, but a wedge consists of two inclined planes put together, 

 so that the work of the plough resolves itself into passing a 

 certain weight of earth (the furrow-slice) up a twisted inclined 

 plane (the wrest). Now a long inclined plane, like a long, easy 

 hill, does not require so much force to go up or to carry 

 anything up as does a short steep one of the same perpendi- 

 cular height. This means that in the plough the short, wide 

 projecting wrest has a greater draught than a long one set to 

 the same size of furrow ; that is, the pressure on the short 

 wrest is proportionally more than on the long one. Now the 

 law of friction is that it varies as the pressure, and is inde- 

 pendent of extent of surface, which is another way of saying 

 that the friction on the short mouldboard is greater than that 

 on the long one, and that therefore the longer it is the 

 better. The longest the writer has ever seen was on the 

 Ballarat plough above mentioned, where it Avas 5 feet, but in 



