Seft. IV. Agriculture and Vegetation. 167 



muft be proportioned to the depth of good 

 foil, 



IT feems flrange, that there is not a 

 more certain way of fixing the depth of the 

 plough, and preferving it in that precife 

 fituation which the foil requires, than the 

 attention of the ploughman. That muft 

 be often fufpended by external objects and 

 fatigue ; and then the cattle and foil fuffer. 

 Does not the wheel-plough remove this 

 objection ? 



THE ftiffer the foil, the oftner mould 

 it be ploughed. Clay cannot be ploughed 

 too often i lighter foils perhaps may. It is 

 allowed by many farmers, that the gravelly 

 foil may be hurt by too frequent ploughing. 



As this operation depends on the prin- 

 ciples of mechanics, and not on thofe of 

 chymiftry, I mail leave it almoft untouched 

 to the confideration of fome other perfon. 

 It is a fubject worthy of attention j and al- 

 M 4 though 



