On Plaister of Paris. 107 



subject, the current opinions of the day. These, like the 

 doctrine of phlogiston, though once held to be so strictly 

 orthodox, may, ere long, become apocryphal ; and be placed, 

 by future reformers in chemiistry, among the lumber of the 

 schools. Something useful, however, is always added to the 

 common stock of knowledge and improvement, by the the- 

 ories of ingenious and scientific men. Yet, after all, the far- 

 mer will find his fields the most convenient laboratories ; his 

 instruments^ of husbandry ^ his safest, most simple and intelli- 

 gible apparatus ; his crops his most instructive expositors j 

 and experience his most faithful and unerring guide. 



