266 The Atmosphere as a SLmrce of Nitrogen to Plants. 
and takes no account of that which the soil has in the meanwhile 
appropriated. To be perfect, these experiments should be made 
simultaneously on the ammonia in the air and in the rain, and 
that absorbed by a given extent of surface-soil. This is a labour 
that we can hardly expect from any one experimenter ; and con- 
sidering the great varieties of soil, the result would even then be 
but an approximation to the truth. For the present we must be 
content with this fact, that a quantity of ammonia and nitric acid, 
equal perhaps on an acre to at least the manuring power of a cwt. 
of guano, is annually brought down to the soil by rain for the 
benefit of vegetation. Let not, however, the cultivator deceive 
himself, and suppose that his duty of manuring his soils is 
lessened from this circumstance. This fall of manure — so to 
speak — it is out of his power to control ; and to it, no doubt, is 
attributable, at least in part, the natural fertility of any given soil : 
his art lies in increasing this natural produce to a point at which 
the crops will repay the cost of their production. But he may 
profit by this newly-discovered bounty of nature if he will take 
full advantage of the atmospheric manure by means of drainage, 
which promotes the equal flow of water through instead of over his 
soil ; by deep cultivation and thorough pulverization of the land, 
which brings every part of it into contact with the air. The 
atmosphere is to the farmer like the sea to the fisherman — he 
who spreads liis nets the widest will catch the most. 
The history of inventions is in nothing more remarkable than 
in the coincidence of time with which many bearing upon each 
other are made. The invention of the electric telegraph would 
have been incomplete but for the almost simultaneous discovery 
of gutta percha, without which submarine communication would 
probably have been unattainable. So, it is to be hoped, the 
knowledge now gained of atmospheric sources of manure will 
soon be followed by a success in adapting that mighty power, 
steam, to the cultivation of the soil ; for nothing is plainer to my 
mind than that abundant cultivation of the soil, if economically 
practicable, is an equivalent to the direct application of manure. 
We draw from our recently-obtained information inducements 
to fresh efforts in this direction, and are led to suggestions 
for improvements on other points of agricultural practice, such 
as green manuring, rotation of crops, and especially irrigation. 
These facts point to most important conclusions ; but at the pre- 
sent moment we must forbear from entering upon them. At some 
future time, when these investigations have led, as they surely 
will, to conclusions of still greater importance, we may perhaps 
be allowed to return to the subject. 
