THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 443 
annual yield of Nitrogen in our crops. The amount of Nitrogen derivable from these 
sources is, moreover, perhaps more readily quantitatively estimated than that from any 
of the other sources enumerated. Accordingly, much labour has, of late years, been 
bestowed in determining the amounts of ammonia and nitric acid in these several aqueous 
deposits.. Extensive series of observations have been made on these points by Boussin- 
GAULT, BarraL, Way, and two of ourselves; and others have experimented on a more 
limited scale. It may be stated, generally, that the rain of the open country has indi- 
cated an average of very nearly the same amounts of ammonia in the hands of Boussin- 
GAULT in Alsace, and of Way and ourselves in England. The most numerous and reliable 
determinations of the amount of nitric acid in rain-water are probably those of Mr. Way. 
By the aid of numerous determinations of the ammonia by ourselves, and of both the: 
ammonia and nitric acid by Mr. Way, we are enabled to form an estimate of the total: 
amount of Nitrogen coming down as ammonia and nitric acid in the total rain, hail, 
and snow, and in some of the minor aqueous deposits, during the years 1853, 1855, 
and 1856, here at Rothamsted, where the experiments relating to the acreage yield of 
Nitrogen in the different crops were made. The result was, that in neither of the three 
years did the Nitrogen so coming down as ammonia and nitric acid amount to 10 lbs. 
per acre. 
Supposing the combined Nitrogen coming down in the direct aqueous deposits were 
to be estimated, in round numbers, at 10 lbs. per acre, per annum, this amount would 
supply less than half as much Nitrogen as was annually removed in the continuously 
grown wheat and barley crops. It would amount to only about one-fourth of that 
which was obtained in the hay, and in the turnips; to a less proportion of that obtained 
in beans; and to a still less proportion of that obtained in the clover. Lastly, it would 
amount to only about one-fourth as much as was obtained per annum, over twelve years 
of ordinary Rotation, but without’ manure of any kind either during that period or for 
some years previously. 
‘We are driven, then, to seek for other sources of the Nitrogen of our crops, than 
that which comes down as ammonia and nitric acid in the more direct and more easily 
measurable aqueous deposits from the atmosphere. Nor does it appear, so far as can 
be judged from the results of Boussin@avLt on this point, that the amounts of combined 
Nitrogen deposited by dew are such as to lead to the supposition that our approximate 
estimate would require any material modification, were as large a proportion of dew 
included in our collected and analysed aqueous deposits as is probably received by the 
soil itself or the vegetation which may cover it. 
(3) With regard to the amounts of combined Nitrogen accumulated by the soil from 
the atmosphere by virtue of surface absorption, or chemical action, it is probable that 
they constitute no inconsiderable proportion of that which is annually available for 
vegetation over a given area of land. Numerous investigations have indeed been under- 
taken during the last few years, both by ourselves and others, to determine the actual or 
relative capacities for absorption of different soils, or constituents of soils. Unfortu- 
