
AS A SOURCE OF THE NITROGEN FOUND IN PLANTS. 593 
cause of the delay which attended the announcement that water is not a simple 
body. CaveENpDisH’s later experiments were repeated by a Committee of the 
Royal Society at his own request, and with entire success ;* and if any one is slow 
to repose faith in chemical experiments made in 1785, let me remind him that 
Farapbay has shewn that every time a friction electric machine is in action, the 
truth of CavENDISH’s observations may be proved, by no more complex device 
than the stretching of a piece of paper wetted with solution of potass, across the 
interval separating two surfaces, between which electric sparks are passing. The 
potass is quickly changed into nitrate of potass.} 
Resting upon these observations of CavenpisH and Farapay, I urge the con- 
clusion, that every lightning flash must convert a portion of the air into nitric 
acid ; and that in tropical regions where thunder-storms prevail, this acid must 
be produced largely and almost constantly. 
Secondly, As for the proposition that the ammonia of the atmosphere is con- 
verted by simple oxidation, as in the process of nitrification at the surface of the 
earth, into nitric acid, | might leave it unconsidered, for my concern is simply 
with nitric acid, not with its source. Iam quite prepared to admit the probabi- 
lity of atmospheric ammonia undergoing conversion into nitric acid; for although 
one condition essential to nitrification in the soil, namely, the presence of an 
alkali or alkaline earth is wanting, yet, from what is known of the intense oxid- 
ising power of ozone, we may well believe that when it is developed in the air, 
as it so certainly and frequently is, it will compel the conversion of ammonia 
into nitric acid. It will presently, indeed, appear, that, from the recent researches 
of Barrat, it is probable that nitric acid is generated in the atmosphere at the 
expense of ammonia. If this, however, be the case, then we must acknowledge 
that, in addition to thunder-storms, a force is constantly at work in the air pro- 
ducing nitric acid; and further, that this force is constantly removing from the 
atmosphere the ammonia on which plants are supposed to be solely dependent 
for nitrogen. 
No data exist from which we can compute, with even an approximation to 
accuracy, the amount of nitric acid produced by thunder-storms all the world 
over. It is certainly, however, considerable, as compared with the amount of 
ammonia in air, and with the amount of nitrogen required by plants. 
It is further uncertain how far temperate regions profit by the nitric acid 
developed by the storms of tropical latitudes; but from the known effects of the 
winds, and of the diffusive force of gases, in spreading through the atmosphere 
substances added to one part of it, we cannot doubt that when the heavy rains 
which so frequently follow thunder-storms, do not at once transfer to the earth 
the nitric acid which they have produced, it will be conveyed, either free or 
combined, to immense distances from the spot where it was developed. But upon 
* Phil. Trams., 1788, p. 261. + Electrical Researches, vol. i., pp. 90, 91. 
