532 Action of Dung and artificial Manures upon Beet-root. 
Possibly therefore a chemist might find the answer in this super- 
abundance of azote, but I am not competent to say how this may be. 
In fact the two leaders in agricultural chemistry, Liebig and 
Boussingault, are at variance on this very point. The two prin- 
cipal results of the experiment seem to be — one, that there is on 
some soils a limit beyond which an additional dose of dung is of 
no use. This result, if confirmed, would be interesting in theory. 
In actual farming there is not much danger of our erring in that 
direction, as to our dressings of dung ; and in some parts of the 
country this would not, perhaps, be a very safe doctrine to 
dwell upon. The other inference, a more practical one, is that it 
is more profitable to use some artificial manures in conjunction 
with dung, than to use either singly. Thus guano and woollen 
rags used singly, added to my crop only 5 tons per acre. The 
single dressing of dung added only 11 tons, and doubling that 
amount of dung did no good; but guano combined with the same 
amount of dung, and rags combined with the same amount of dung, 
each gave an addition not of 16 tons of roots, according to their 
effects when used singly, but of 20 tons, yielding each 36 tons, 
a produce very large indeed for land which, four years ago when I 
took it in hand, was said to be incapable of growing a turnip. I 
Avill only add, that I am not insensible to the risk, in drawing 
general rules, from single experiments, however carefully made ; 
but as this experiment was a careful one, I state what appear to 
me to be the legitimate inferences from it, in the hope thac they 
may be confirmed or refuted by other observers, so that at last 
the truth may be known. 
Pusey, November 24, 1845. 
XLV. — On the Nature and Causes of the Decay in Potatoes. 
By Dr. Lyon Play fair. Consulting Chemist to the Society. 
Lecture I. 
On former occasions I have ventured to address you on the an- 
nexion between practice and science, and you bore any practical 
ignorance which I might have manifested in the belief that 1 was 
anxious carefully to cull the fruits of your experience, and to 
select them by the light which 1 had borrowed from the brilliancy 
of those philosophers who by their discoveries have made mankind 
their debtors. 
I always contended that practice was so much in advance of 
theory, as far as related to. agriculture, that it was the duty of the 
scientific man not to diverge into "jxistures new,'' but to cndca- 
