JANUARY 4, 1884.] 
natural agencies which tend to remove nitrogen from 
the soil, had undisputed possession of the field. When 
the manuring was discontinued, the losses of nitro- 
gen, according to Dehérain’s results, sank very mate- 
rially, though still remaining considerable. 
From the combined results of both these investiga- 
tions, it would appear that we may fairly conclude, 
that, under ordinary conditions of tillage, there is con- 
siderable loss of nitrogen from the soil. Lawes, Gil- 
bert, and Warington’s experiments show that much 
nitrogen may escape in the drainage; and, according 
to their calculations, more nitrogen was removed from 
six out of thirteen of their experimental plots in crop 
and drainage, during thirty years, than was supplied 
in the manure. From Dehérain’s experiments we 
learn that a soil under constant tillage may grow 
poorer in nitrogen in spite of heavy manuring. In 
fact, of all the elements of the soil which are required 
for plant-growth, nitrogen is one of the most mobile. 
The soil, it is true, has the power of fixing ammonia 
in insoluble combinations; but both ammonia and 
organic nitrogen are constantly being converted into 
nitric acid in every fertile soil, and this compound 
the soil has no power to retain. Under natural con- 
ditions, when the soilis thickly covered with vegeta- 
tion, this nitric acid is assimilated by the roots as 
rapidly as it is formed, while the compact state of the 
soil hinders access of oxygen to the deeper layers, and 
thus moderates nitrification. This action of plant- 
roots in arresting nitrates on their way to the lower 
strata of the soil is shown very plainly in Lawes, 
Gilbert, and Warington’s experiments already cited. 
While the land carried a crop of wheat, the drain-water 
contained little or no nitrates, except when an excess 
of nitrogen had been given in the manure; but as 
soon as the crop was removed, nitrates made their 
appearance in the drain-water. 
But an untilled soil is not only protected against 
losses of nitrogen: it is also in condition to retain the 
nitrogen brought to it in rain, snow, etc. This comes 
partly in the form of ammonia, which is fixed by the 
soil, and partly in the form of nitric acid, which is 
fixed by the vegetation. In this way a soil carrying 
permanent vegetation may be continually gaining 
nitrogen. This is indicated by Dehérain’s results on 
the esparcette plots, and, aside from them, is suffi- 
ciently evident from the facts, that at some period of 
the world’s history all its nitrogen must have existed 
in the free state, and that, so far as we know, the 
combined nitrogen of atmospheric precipitates is 
the sole natural source of nitrogen to the soil. 
Tillage alters this state of things very materially. 
By breaking up and mellowing the soil, it facilitates 
the access of oxygen, and increases the rapidity of 
nitrification. At the same time, the natural vegetation 
is replaced by one occupying in many cases but a part 
of the ground, and occupying it for but a portion of 
the year. Add to this that by diminishing the amount 
of vegetation we diminish the evaporation of water, 
and thus leave the soil moister, and at the same time 
expose it more fully to the sun’s rays, thus rendering 
it warmer, both of which conditions favor nitrifica- 
tion, and we see that cultivation both increases the 
SCIENCE. | 19 
flux of nitrogen in the soil, and decreases the means 
of utilizing it. 
The clear recognition of this state of things brings 
with it the suggestion of at least a partial remedy, 
which is to keep the soil occupied as fully and as long 
as possible with growing vegetation. The roots of the 
living plant lend to the soil an absorptive power for 
nitrogen compounds, similar to that which it has of 
itself for other elements of plant-food, and enable it 
to store up these compounds against future needs, 
To prevent a loss of nitrogen, we must make use of 
this power as fully as possible, both in the system of 
cultivation adopted, and in other ways. After taking 
off a crop in the early fall, instead of leaving the land 
bare, let it be sown with some quick-growing crop, e.g., 
rye, which shall serve solely to store up the nitrogen 
which would otherwise be lost. In the spring this 
crop is ploughed under, and furnishes nourishment for 
the succeeding crop. Such a plan has been adopted 
here and there with advantage. Its general use would 
turn largely, of course, on the question of expense. 
On a virgin soil containing already large reserves of 
nitrogen, no appreciable benefit might result from it, 
though even there the preservation of the present 
fertility is worth striving for. But between this con- 
dition and the state of relative exhaustion to which 
the soil of our older states has been reduced, there 
must be a point where saving nitrogen in this way 
would be of immediate as well as prospective benefit. 
The exact methods of applying the principle involved 
to particular cases it is not the province of this article 
to discuss. The principle itself, however, is very 
simple. Keep growing roots present in the soil as 
long and as extensively as possible to seize upon the 
nitrogen (and other elements as well) which will 
otherwise be washed out of the soil, and to store it 
up in insoluble forms, ready for the needs of future 
crops. H. P. ARMSBY. 
THE LIFE OF HAMILTON. 
Life of Sir William Rowan Hamilton, Knt., LL.D., 
D.C.L., M.R.I.A., Andrews professor of astron- 
omy in the University of Dublin, and royal astron- 
omer of Ireland, ete. : including selections from his 
poems, correspondence, and miscellaneous writings. 
By Rosert Percevar GRAVES, M.A., snb-dean 
of the Chapel royal, Dublin. Vol. i. London, 
Longmans, Green, § Co., 1882. 20+698 p. 8°. 
Turis volume, which forms one of the latest 
issues Of the Dublin university press series, 
has been prepared partly through the assist- 
ance furnished by the Board of Trinity college, 
and published by the provost and senior fel- 
lows. Mr. Graves had at first, however, un- 
dertaken the biography of Hamilton:on his 
own responsibility, and unassisted in the labor 
which it involved; and we ought not to pass 
unremarked his especial fitness for the per- 
formance of this arduous task. In the first 
place, he was unconnected with Hamilton by 
