90 Home Produce, Imports, Consumption, and 
produce in the better seasons, and somewhat too low a, pro- 
duce in unfavourable seasons. 
If, then, as a careful examination of the facts seems to indi- 
cate, the yield of the unmanured plot has somewhat declined 
from exhaustion, and that of the farmyard manure plot has in a 
rather greater degree increased from accumulation, whilst the 
produce of the selected artificially manured plots has not 
changed otherwise than from year to year, according to the fluc- 
tuations of the seasons, the question arises whether, or to what 
extent, the average results of the whole of the selected plots 
should be considered inapplicable as a basis for estimating the 
yield for the United Kingdom each year, either during the past 
forty years, or in the future. 
In order to form a judgment on this point, the produce of 
the unmanured plot in each of the past forty years has been in- 
creased in the proportion in which the previous calculations 
showed that there had probably been decline from exhaustion, 
and that of the farmyard manure plot has been reduced in the 
proportion in which the calculations showed that there had pro- 
bably been increase from accumulation. That is to say, the 
actual results have been corrected on the assumption that there 
had been neither decline from exhaustion in the one case, nor 
increase from accumulation in the other. Then, the average of 
the thus corrected produce of the unmanured and of the farm- 
yard manure plot, and of the three artificially manured plots 
(which are supposed not to have changed) taken as one, has 
been calculated, and this corrected or calculated average pro- 
duce of the selected plots each year has then been deducted from 
the average of the actual average results, the difference showing 
the excess of the actual over the calculated result each year, due 
to the greater increase by accumulation on the farmyard manure 
plot, than decline by exhaustion on the unmanured. The result 
indicates an average over the forty years of rather more than 
half a bushel excess of produce per acre per annum ; and an 
excess of rather over a bushel in the fortieth year, supposing 
the rate of increase had been uniform throughout the period. 
Whether or not this change vitiates the applicability of the data 
as hitherto used, or their utility for the same purpose in the 
future, will be better seen farther on. 
It has already been explained, that the average produce of 
the selected plots probably indicates somewhat too high a 
result for the United Kingdom in seasons of great abundance, 
and too low a result in very unfavourable seasons, and that, 
accordingly, in some seasons a higher or a lower figure has been 
adopted ; but that the estimates so founded on the produce of 
