for Twenty Years in succession on the same Land. 
99 
Notwithstanding tliis, what does he say now ? He ignores 
his former arguments and views. He repudiates the obvious 
meaning of the terms he employed. He attributes to his oppo- 
nents ignorance of the fact that, in a special scientific sense, 
ammonia-salts are mineral substances. He says — " All the ma- 
terials constituting the food of our cultivated plants belong to 
the mineral kingdom." And — "Sulphate of ammonia and sal- 
ammoniac are mineral , . . ." Thus, ammonia is now claimed 
as a mineral manure, instead of antithetic to it, as throughout 
his earlier writings ; and, accordingly, he claims as consistent 
with his " Mineral Theory," any beneficial effects from the use 
of nitrogenous manures. He would, indeed, have it supposed 
by the rising generation of readers, and if possible established 
for the future, that the "Mineral Theory" of Agriculture which 
has been in controversy is the " Mineral Theory " of vegetation 
in genera], according to which, as distinguished from the so- 
called "Humus Theory," all the food of plants is mineral. 
Having made these fundamental changes, without acknow- 
ledgment of either change or error, he endeavours to divert the 
attention of his modern and future readers from his earlier works 
and editions, and insinuates that the error has been on the side 
of his opponents. Thus, in 1870, in the course of a disquisition 
on the claims of t7'ufh in scientific inquiry, he speaks of his 
long forbearance in reference to the opposition to his views on 
tlie theory of fermentation, the sources of muscular power,^the 
formation of fat, &c., and, in agricultural chemistry, on the 
laws of the nutrition of plants and animals. But, he goes on to 
say, there is for every one a limit, when it becomes his duty 
again to contend for that which he holds to be true, and this is 
reached, when error has gained the victory, and scarcely a doubt 
is expressed that it may be the truth. Then, with more special 
reference to the controversy with ourselves, he proceeds — 
"In this way it happened to my views on agriculture, on the 
causes of the exhaustion of soils, and the conditions of the 
restoration of their fertility ; in the 16 years which elapsed 
between the sixth and seventh editions of my book, my doctrine 
was as good as buried, by the majority of practical agriculturists 
it was held to be completely refuted, which might well be 
quite unhesitatingly assumed, since one of the most renowned 
Scientific Societies had bestowed its great gold medal upon my 
most persevering opponents, as a seal of their triumph over 
the mineral theory. With the publication of the seventh edition 
ot my 'Chemistry in its applications to Agriculture and 
Physiology,' a refutation of my doctrine is no longer spoken of, 
and the younger generation of farmers, standing in a far higher 
scientific position, no longer comprehend how there was so 
H 2 
