ADVERTISEMENT, 
During ten years, from 1802 to 1812, I had the 
honour, every Session, of delivering Courses of 
Lectures before the Board of Agriculture. I en- 
deavoured, at all times, to follow in them the 
progress of discovery ; they therefore varied every 
year : and since they were first published in 1813, 
some considerable improvements have been made 
in chemical science, which have rendered many 
alterations and additions necessary. 
I am indebted for much useful information to 
many gentlemen who have endeavoured to improve 
Agriculture, and to apply scientific principles to 
this most important of the arts ; of which acknow- 
ledgments will be found in the body of the Work. 
I hope there are no omissions on this head ; but 
should they exist, I trust they will be attributed to 
defect of recollection, and not to any want of 
candour or of gratitude. 
Where I have derived any specific statements 
from books, I have always quoted them ; but I 
have not always made references to such doctrines 
as are become current, the authors of which are 
well known ; and which may be almost considered 
as the property of all enlightened minds. 
In revising this work for the fourth edition, I 
have been forcibly struck with its imperfections, 
