FEBRUARY I, I9I7| 
NATURE ~ 
431 
diminution has affected a wide area, and thus 
suggests a cause operating on a large part, if 
not the whole, of the earth’s surface; while, as the 
supply basin is limited in valley glaciers, it would 
require a considerable rise or fall in the mean tem- 
perature materially to affect the volume of them, 
neither of which has been observed. Still, an 
increased or diminished precipitation of snow on 
the névé of the ice-stream would affect the latter, 
besides altering the surface ablation of the stream 
itself. But as the amount of precipitation in- 
creases in ascending a mountain range from the 
lowlands, and then diminishes, much may depend 
upon the position of the zone on which it is at 
a maximum. As that zone probably does not 
exceed, at any rate in the Alps, a thousand feet 
Fic. 2.—The Rhone Glacier on August zo, 1912. 
vertical, rather small variations in the mean tem- 
perature or snowfall of a region may produce 
somewhat marked effects. The last period of 
diminution, now more than half a century, seems 
to bear no relation to either the eleven-year sun- 
spot period or Briickner’s thirty-five-year one, 
and thus suggests a complication of causes. Be 
that as it may, in this memoir on the Rhone 
Glacier the variations in its length, area, volume, 
and level, the snowfall and ablation, the move- 
ment of its several parts, and the relation between 
the velocity of the surface and the thickness of 
the ice, are all placed on record, so that students 
of glaciers owe a debt of gratitude to the authors 
of this volume and the Swiss Natural History 
Society. T. G. Bonney. 
NO. 2466, VOL. 98] 
SOURCES OF NITROGEN COMPOUNDS 
IN. THE UNITED STATES. 
Ream problem of how to turn the vast store of 
uncombined nitrogen which exists in the 
atmosphere into useful products may be said to 
have been only seriously attacked within the life- 
time of the present generation. It had its origin 
in the growing demand for forms of combined 
nitrogen suitable for use in the arts, and more 
particularly in agriculture, the oldest of all the 
arts. But circumstances arising out of the present 
world-wide struggle, affecting in greater or less 
degree every nation, but more particularly those 
engaged in the war, have forced the problem into 
still greater: prominence by demonstrating how 
intimately it is bound up with the question of 
national defence. Indeed, as regards the Central 
Powers, their very existence is dependent upon 
it, as they now painfully realise. 
Accordingly nearly every highly developed 
nation is considering it, and its urgency is shown 
by the circumstance that its solution is no longer 
left wholly to individual effort or private enter- 
prise. Even our own Government, hitherto not 
very prompt to initiate action in such matters, 
has been moved to recognise its national import- 
ance, and has got so far.as to appoint at least two 
' committees associated with public departments to 
consider and report upon it. 
In this connection it is of interest to note how 
the question. strikes American expert opinion. 
This is revealed in the publication before us by 
Dr. C. G. Gilbert, recently issued by the 
Smithsonian Institution. 
As the author points out, in the extension of 
chemical needs,.as inthe development of cyaniding 
in industry, of refrigeration in the preservation of 
foodstuffs, and more especially in the increased 
use of fertilisers, nitrogen compounds are now 
necessary not only to the welfare, but to the very 
existence of a people living under modern con- 
ditions of economic development. Until within a 
few years past, the yields from India, from Con- 
tinental sewage-farms, together with the natural 
supplies from -South America, have met the 
demand for nitrates. Ammoniacal compounds 
have been produced in rapidly increasing quanti- 
ties, as by-products, in the various methods of 
the destructive distillation of coal, peat, and oil- 
shale ; in producer and blast-furnace gas; in bone 
carbonising, in sewage and garbage disposal, and 
in a variety of other methods; and the sulphate 
of ammonia thus obtained bids fair to overtake, 
if not largely to supplant, Chile saltpetre as a 
fertiliser. But even these combined sources are 
now proving inadequate to meet the world’s de- 
mands, and the increasing necessity has stimulated 
efforts to effect the synthetic production of 
ammonia and nitric acid from atmospheric 
nitrogen. 
Of the several methods of accomplishing this 
synthesis there are at present, so far as is known, 
‘only three which are commercially practicable, 
1 “*Sources of Nitrogen Compounds in the United States." By Dr. C. G. 
Gilbert. (Smithsonian Institution, Washington, 1916.) 
