614 
(vol. xxxiii., No. 1). The first discovery of silver was 
made in the district in July, 1903, and the progress made 
since that date is described in detail. The characteristic 
rocks of the region are conglomerates of Lower Huronian 
age, through which, and sometimes through the under- 
lving diabase, pass calciferous carrying metallic 
silver and sulphides or arsenides of silver with smaltite 
and niccolite, the arsenides of cobalt and nickel. The 
veins occur along the main lines of fracture by which the 
conglomerate has been shattered. 
of the deposits, different opinions have been ex- 
pressed, but with increasing experience the trend of 
opinion is towards a long life for the district. 
veins 
As to the permanency 
very 
In addition to the usual record of measurements taken 
during the year 1906 at Epsom College, the report of the 
college Natural History Society for last year gives the 
average height, weight, and chest girth of all boys who 
have been measured in the ten years 1897-1906, and a 
chart showing average grades of development for the same 
period. On the whole, the average Epsom College boy 
would appear to be rather superior in physique than 
inferior to the average public-school boy. One marked 
exception is evident in the curves for the ages 17 yr. 10 mo. 
to 18 yr. 4 mo., though it must be stated that the number 
of observations on which the curves are based is, 
these months, much smaller than the rest. 
for 
Boys at Epsom 
College between these ages, however, during the last ten 
years appear to have been on a lower physical grade than 
at other ages. The other contents of the society’s report 
show that excellent field work continues to be done by the 
members, among whom geology, botany and meteorology 
appear to be equally popular. é 
Tue subject of the perception of relief was discussed 
in letters to Nature of January 3 and 31 last (vol. Ixxv., 
pp. 224 and 321), and the same question is raised in a 
communication received from Mr. R. T. A. Innes, of the 
Transvaal Meteorological Department. Mr. Innes  de- 
scribes a method of seeing stereoscopic pictures in relief 
without the use of a stereoscope, explained to him by 
Colonel W. G. Morris. If while steadily viewing a 
distant object an index finger be held before the eyes, two 
images of it are seen; if now the other index finger be 
held before the eyes also, four images will be seen. By 
a little adiustment of the distance of the fingers from the 
eye, the two central images can be superposed. The 
substitution of a stereoscopic picture leads to similar 
results, and the superposed images give the idea of relief. 
Mr. F. A. Linpemann and Mr. C. L. Lindemann, writing 
from Darmstadt, describe a new glass which is transparent 
to rays of very short wave-length. They have found that 
lithium biborieum, Li,B,O, (ordinary borax in which the 
sodium is replaced by lithium), when fused produces a 
clear glass which shows no appreciable absorption in the 
ultra-violet spectrum above 2000 A. The aluminium 
line 1856 is distinctly visible, though somewhat weakened, 
if the glass be too thick. In order to determine the 
absorption below this a vacuum spectrograph would 
naturally be required, as the air absorbs any lines shorter 
thn 1856. The refractive index for the D-line n=1-5389, 
the dispersion A between e and F, A=0-00847, and 
v j—1/A=63-7. As might be expected, owing to the 
4 2 percentage (82-5) of boracic acid, the dispersion 
toward the red side of the spectrum is fairly large, whereas 
that toward the violet side is very small. The glass is 
extremely transparent to R6ntgen rays, which it lets 
through, roughly, ten times as well as ordinary glass. 
NO. 1956, VOL. 75 | 
NATURE 
[APRIL 25, 1907 
The specific gravity is 2-2; the hardness, 6. The glass 
can be cut and polished without difficulty. The cubical 
expansion coefficient (calculated from the constants of 
Winkelmann and Schott) is 118-10-7, about half that of 
ordinary glass. It has been found that, as a general rule, 
the transparency for rays of short wave-length increases 
in analogous salts as the atomic weight of the metal 
decreases, but sufficient experimental data have not yet 
been obtained to warrant the publication of a definite 
formula, 
A xew high-tension condenser on the Moscicki principle 
is likely to prove a useful commercial apparatus if, after 
testing in practical work, it fulfils the advantages claimed 
for it in a very complete and interesting pamphlet which 
we have received from Messrs. Isenthal and Co., who are 
agents for the makers. A condenser made on this prin- 
ciple is now on view in London, and the construction is 
very neat and convenient, any number of condenser 
elements being grouped together in a battery very easily 
according to the voltage required. The chief advantages 
claimed over other condensers are the (1) strengthening 
of the dielectric to minimise the chances of rupture; 
(2) perfect contact between dielectric and armature plates; 
3) prevention of local heating by means of a cooling 
chamber; (4) no organic substances These con- 
densers have been used successfully for the protection of 
live wires against atmospheric discharges; wireless tele- 
graphy; suppression of lag in alternating currents; and 
in X-ray and the construction of the condenser 
certainly renders it much less liable to breakdowns, which 
in practical serious. The opening in 
wireless telegraphy work alone for a condenser which can 
be depended upon is very great, and the new condenser 
will no doubt be given a thorough trial in many ways, as 
a practical commercial condenser has long been demanded. 
used. 
work ; 
work prove very 
A SECOND communication on anode rays is published by 
Messrs. Gehrcke and Reichenheim in No. 4 of the Verhandl- 
ungen of the German Physical Society (compare Nature, 
this vol., p. 173). An arrangement of apparatus is de- 
scribed by means of which the phenomena produced are 
made very striking by using high potentials obtained with 
anodes permitting of more continuous working in a high 
vacuum. <A brilliant fluorescence is observed on _ per- 
mitting the ‘‘ rays’? from the anode to impinge on a mica 
screen or on the glass walls of the vacuum tube. The 
colour of the fluorescence is the same as that of the 
emission spectrum of the metal present in the salt used 
at the anode; thus with lithium carbonate the light is 
reddish in colour, and in the spectroscope shows the red 
and orange lines of lithium. The admixture of another 
substance, such as graphite or zinc dust, with the salt 
used as anode facilitates the formation and improves the 
character of the rays. It is noteworthy that the anode 
rays cannot be produced from a cold anode, and that 
usually some interval elapses, during which heating 
occurs, after the current has been switched on before they 
make their appearance. The volatilisation of the salt 
nay therefore play an important part in their production. 
‘ 
ce 
Since ‘‘ synthetic ’’ indigo was put upon the market in 
1897, some uncertainty has existed regarding its tinctorial 
value as compared with the natural dyestuff. The 
makers of synthetic indigo have maintained that the only 
significant constituent of natural indigo is  indigotin, 
identical with the synthetic substance, and that the other 
components present in the natural dye are either inert or 
harmful impurities. On the other hand, certain practical 
