Xviii' INTRODUCTION. 



ber of sound practical facts: the author, however, 

 was evidently not a chemist. Wallerius was suc- 

 ceeded by several other authors, amongst whom 

 ought to be mentioned Cullen, Pearson, Gyllenborg, 

 De Beunie, Ruckert, Einhof, and Dundonald ; but 

 the speculations of these authors (though ingenious) 

 were, for the most part, crude and incomplete. The 

 writings of Einhof were valuable for the numerous 

 accounts of careful experiments which they contain ; 

 the analyses, though not carried to that degree of 

 minuteness which subsequent discoveries led to, were 

 trustworthy and accurate, and, as such, will always 

 continue of value. Humboldt's Sketch of the 

 Chemical Physiology of Vegetation, which appeared 

 at this time, is a book of far higher talent than those 

 just mentioned, and contains enlarged views and 

 cautious generalizations, which the subsequent pro- 

 gress of science has in most cases confirmed. At 

 the commencement of the present century, when 

 Organic Chemistry was rapidly advancing, Berzelius 

 and Davy endeavored to apply the conclusions to be 

 derived from chemical experiments, to agriculture. 

 If the deductions which they made were not always 

 correct, and if the plans which they proposed did 

 not always produce the effects which the authors 

 anticipated, it must be remembered that thev were 



