40 *fbe "Principles of Part II, 



IF earth is exhaufted of its vegetable 

 food, experience has difcovered, that it re- 

 covers it again, if allowed to lie idle. This 

 fhows, that the vegetable food is continual- 

 ly on the increafe, when the earth is not 

 robbed of it by the crops it bears. We dif- 

 cover immediately whence this food comes, 

 when we attend to thefe two fads j . that 

 the more the foil is expofed to the air, the 

 vegetable aliment is the fooner procured, 

 and in greater quantity too ; and that when 

 the furface is buried by the action of the 

 plough, and a new foil brought up, that 

 foil, though feemingly as good as the for- 

 mer, produces bad crops, till it has re- 

 ceived for fome years the benefit of the at- 

 mofphere. 



FALLOWING is a conftant proof of this. 

 The foil is frequently broke down and 

 turned over by means of the plough, and 

 every part of it is expofed to the influence 

 of the air. That the communication of 

 the earth, by the mechanical a&ion of the 



plough, 



