[ 5 3 



which experience would ferve but as a very imper- 

 fect inftru&or. 



It is indeed impoflible for any man who pra&ifes 

 agriculture to avoid obferving, that better or worfe 

 crops may be obtained from the fame field in diffe- 

 rent circumftances, and that certain foils are better 

 adapted to yield good crops of one kind of produce 

 than of odiers. It is as impoflible for a man, whofe 

 fubfiftence depends upon the produce of his fields, 

 to avoid forming conjectures as to the caufes of 

 thefe diverfitiesj and in the courfe of a long and 

 attentive obfervation it muft probably happen, that 

 fome of thefe conjeftures may be right. But as this 

 judgment is formed merely from a complex view of 

 the whole, in which a great variety of particulars are 

 blended indifcriminately together, it is impoflible for 

 the mind to diftinguifti in this way, with any degree 

 of certainty, thofe circumftances that are of ejfential 

 from thofe that are of trivial importance. The im- 

 agination is thus left at full freedom to exert its in- 

 fluence; and ill-grounded theories fo warp the mind 

 as to make it believe that it fees certain fa6ts as 

 clearly proved, which are nothing elfe but a fpecious 

 delufion. Nor is it pofllble ever to corredt the 

 falfe judgments that are thus formed, but by calling 

 in the aid of experiment; which, by carefully fepa- 

 B 3 rating 



