27 



What theorists call the prejudice of* prac- 

 tical men is not so obstinate but what 

 it will learn if they can teach it any thing 

 to its own interest. " Physician heal thy- . 

 self," The conceit of the closet can only 

 be cured by practical out-door proof. 

 When chemists make their fortunes as 

 farmers or gardeners, farmers and gar- 

 deners will follow their example. In the 

 meantime those who have to do cannot 

 afford to spend a life in labour, the product 

 of which is a doubt. 



According to an experiment of Hales, 

 which has been since verified by others, the 

 sap rises with a force sufficient to support 

 the pressure of a column of water of double 

 the height which would burst an ordinary 

 hogshead cask. And we see that it ascends 

 to prodigious heights, yet we are ignorant 

 how, or from w^hence, it is first absorbed, \ 

 and we are ignorant of the mechanism^ 

 that is, of the cause and laws, by which 

 it is forced up. 



