t -63 ] 



the hufbandman. The philofopher may amufe 

 himfelfby enquiring after firft principles, and the 

 elennentary parts of bodies, but the farmer fnould 

 never be diverted from a profitable pracT;ice, until 

 one more fo is recommended by the fuccefs of re- 

 peated experiments. 



Various are the opinions of the learned concern- 

 ing this matter. Some fuppofe the food of plants 

 to be water; fome earth; others air, nitrous falts, 

 oil, &c. &c. perhaps all of them wide enough of 

 the mark. It muft be confeffed, we know nothing 

 of the eiTence of things. We are not endued with 

 faculties equal to the curious refearch. Things are 

 known to us by their properties only. But what 

 are their properties by which they are knov/n to us, 

 but certain powers to affeft us in a particular man- 

 ner, and to imprefs different fenfations and per- 

 ceptions on our bodily organs? Thefe different 

 perceptions, indeed, enable us to diftinguifh, ac- 

 curately enough, one thing from another; but we 

 are totally ignorant of the nature of thofe powers, 

 and equally fo of theeflence or lubftratum in which 

 they inhere, and by which they are fupported. 



The great fyftem of the univerfe is governed by 

 general laws, which, fo far as our knowledge ex- 

 tends, obtain univcrfally. Gravitation, attradion, 

 repulfion, cohefion, and perhaps many other prin- 



M 2 ciples. 



