256 NATURE 
[ NovEMBER 30, 1916 
Spanish cedar (Cedrela odorata) and the quebracho are 
the most important. These are more than sufficient 
to meet the home demand, and are largely exported, 
but at the same time short-sighted exploitation bids 
fair to impair seriously this industry. On the other 
hand, it is, of course, quite possible that further study 
of the timber resources will result in the discovery 
of other hardwoods of commercial value. Of more 
economic importance is the supply of softwoods. The 
Parana pine (Araucaria brasiliensis) of southern Brazil 
and the Chilean pine (A. imbricata) seem to be the 
only two species of importance, and are being in- 
creasingly used in place of imported coniferous wood 
from the northern hemisphere. But the limited area 
of these softwoods and the growing demand for cheap 
timber make it improbable that South America can 
ever dispense with her timber imports, and certainly 
there is no hope of her being able to export soft- 
woods. In view of this paucity of timber there is 
urgent need of the South American States instituting 
scientific management of their forests and the pre- 
vention of undue exploitation. South America is far 
less rich in commercial timber than might be supposed, 
and her resources are not inexhaustible. 
Tue retreat of the Barry glacier in Prince William 
Sound, Alaska, has been studied for many years. 
In 1910 the National Geographic Society’s expedition 
showed that the face had withdrawn three miles since 
1899. This expedition gave an exhaustive account of 
all observations previous to 1910, Later observations 
are contained in a brief paper by Mr. B. L. Johnson, 
published as Professional Paper 98 C of the United 
States Geological Survey. Mr. Johnson _ visited 
the glacier in 1913 and 1914, and found in both years 
that the rate of retreat had been maintained. Be- 
tween 1910 and 1914 the rate of retreat was $200 ft. 
on the eastern side, and about 2500 ft. on the western 
side. The rate on the western side seems to have 
decreased after the uncovering of bedrock on that 
side. The paper is illustrated with several photo- 
graphs of the glacier in various stages of its retreat. 
Some details of the Indo-Russian triangulation con- 
nection are given in the Geographical Journal for 
November (vol. xlviii., No. 5). By 1911 Gilgit had 
been connected with the Indian system, and the Rus- 
sians on their side had reached Pamirski port in about 
lat. 38° 13’ N., long. 75° E. But the connection of 
Gilgit with the Russian survey across a strip of 
Afghan territory presented difficulties of a formidable 
nature, as it involved the crossing of the Karakorams. 
The only feasible route was from Gilgit up the Hunza 
valley to the Kilik Pass, involving the survey of about 
one hundred miles up a narrow, precipitous-sided 
gorge, flanked by mountains rising 6000-7000 ft. above 
the valley floor. The number of stations in this survey 
was thirty-three, and their average height is 16,222 ft. 
The work was carried out in the face of great difficul- 
ties and hardships by the late Lieut. H. Beli, R.E., 
in 1911 and 1912, and completed by Lieut. Mason in 
1913. A report of the work is contained in the Records 
of the Survey of India, vol. vi. Capt. R. W. Hing- 
ston, I.M.S., has some notes of the geology and 
climate, as well as a valuable paper on his observa- 
tions of blood at high altitudes. 
Some observations on the bai, or so-called ‘‘sand- 
mist,’ a phenomenon of frequent occurrence’ in the 
Far East, are contributed by Prof. Yuji Wada to 
Temmon Geppo, the organ of the Astronomical Society 
of Japan (vol. ix., No. 6, August, 1916). The mist, 
which is ascribed to an atmospheric depression over the 
sandy Tsai-pih district of Central China, is prevalent 
in spring. In winter the ground is frozen, and in 
summer it is knit together by grass, but between these 
NO. 2457, VOL. 98] 
seasons the loose surface is churned up by the wind, 
and clouds of sand rise to a great height and are 
carried eastward, afterwards collecting moisture and 
falling as a coloured mist. Dusing the fall the sun 
is obscured and objects assume a yellow or ashy hue, 
the conditions closely resembling those attending a 
solar eclipse, for which the phenomenon was often 
mistaken by ancient chroniclers. Characteristic of the 
bai is the thick coating of very fine yellow dust which 
settles everywhere. During a sand-mist at Chemulpo 
on March 4, 1915, the author measured a fall of sand 
on a sheet of glass in an underground chamber pro- 
tected from the wind. A twenty-four hours’ deposit 
on 118-6 sq. cm. weighed one centigram. On the same 
day a fall of } in. was recorded in Etchu province, 
Japan. Sometimes the sand descends in a rainstorm. 
An instance is cited of a violent storm of orange- 
coloured rain in 1306, which caused the deaths of 
many persons and cattle. The author concludes that 
the bai is akin to the ‘‘blood rain”’ and ‘‘red snow” 
familiar to European meteorologists. 
Tue July issue of the Agricultural Journal of India 
(vol, xi., part 3) contains an article on ‘‘ Photographic 
Illustration,” by Mr. C. M. Hutchinson, which will be 
very helpful to the many scientific workers whose im- 
perfect acquaintance with the limitations of the half- 
tone process of reproduction of photographic illustra- 
tions has so often led to unexpected disappointment. 
The questions of lighting, exposure, development, class 
of plate, and use of light filters are discussed and well 
illustrated by an excellent series of reproductions. 
Tue last two parts of the Edinburgh Mathematical 
Society’s Pticensidee (May and September, 1916) con- 
tain the usual amount of interesting matter. Perhaps 
the most important paper is that of Dr. J. Dougall on 
the solution of Mathieu’s differential equation; this 
equation is important for physical applications, and 
Dr. Dougall has found solutions adapted for computa- 
tion. Possibly they are not the proper analytical forms ; 
these may be quotients of integral functions, as in 
the case of the proper representation of the elliptic 
functions; but the paper certainly shows an advance 
on the practical side. Other papers deserving atten- 
tion are Mr. Brown’s on Fourier’s integral, Mr. 
_Milne’s on differential equations, Mr. D. G. Taylor’s 
on linear substitutions, and Mr. Tinto’s on space 
transformations. We have also received Nos. 19 and 
20.0f the same society’s Mathematical Notes; they 
show that the study of mathematics at Edinburgh is in 
a very healthy condition, and contain a number of 
elegant demonstrations. 
Tue researches of Prof. Kamerlingh Onnes have 
shown that at temperatures below 4° or 5° on the 
absolute scale mercury, tin, and lead have extremely 
small electrical resistances. If the temperature of a 
wire of either of these materials in this super-conduct- 
ing state is gradually increased, at a certain tempera- 
ture known as ‘‘the critical temperature” the resist- 
ance rapidly increases. If the wire is subjected to a 
magnetic field this critical temperature is lower than it 
is in the absence of a field. If the current used in 
testing the resistance is increased, the critical tempera- 
ture is also lowered. In the Journal of the Washing- 
ton Academy of Sciences for October 19 Mr. F. B. 
Silsbee, of the Bureau of Standards, makes use of the 
experimental data available to show that the effect of 
the increase of the testing current on the critical tem- 
perature is due entirely to the magnetic field that 
current produces. This accounts for the differences 
observed in the effect of the current according to 
whether the wire used in the tests is straight or 
coiled. If further work supports Mr. Silsbee’s theory, 
it should afford a clue to a more satisfactory explana- 
: tion of the super-conducting state. 
