PHYSICAL AND LITERARY. 71 



experiments, after many comparative 

 trials ; but, for aught we know, ic may be 

 the refuk of imitation only. In the 

 neighbourhood, fballow ploughing h 

 proper; and the example is perhaps blind- 

 ly followed, without attending to the dif- 

 ference of circumltances. 



Dropping then authority and pracr 

 tice, from which fo little fatisfadtion can 

 be obtained, the only refource left us is, 

 to recur to principles and rational con- 

 fiderations ; which, at the fame time, £ 

 am afraid, will not carry us far ; as feve- 

 ral articles are necefTary to be eftabliflied 

 by experiments before a conclufive ar- 

 gument can be formed. One caoital 

 article is, At what depth from the fur- 

 face roots produce their flrongefl; effecls ? 

 Concerning this article, there is nothing- 

 afcertained with any degree of accuracy, 

 further than in general, that fome roots 

 pierce deeper than others, and that many 

 roots, even of corns, produce vigorous 

 effeds much lower down than three 

 inches. Were arguments a priori to be truit- 

 ftd, independent of experiments, one would 



believe, 



