32 
identical optical properties. Brilliant green alone in thin layers 
is blue rather than green, and though it shows dichromatism, the 
change from blue to red is not nearly so striking as a change 
from green to red. The prisms can be made in the following 
way. 
A quantity of Canada balsam is boiled in an evaporating dish 
until a drop placed on a cold surface becomes quite hard. The 
dye must not be added until the balsam has cooled almost to the 
point of becoming thick, otherwise it will be decomposed and a 
very muddy green result. 
Enough brilliant green must be dissolved in the balsam to 
make it appear deep red in layers 1°5 cm. thick. Thin layers 
will be found to be blue. The naphthol yellow is now added in 
quantity sufficient to change the tint of thin layers from blue to 
green. Possibly some samples of the dye will not require the 
addition of the yellow, but all which I have tried are improved 
by the process. A hollow prism is now made by fastening two 
pieces of thin plate glass between two grooved strips of wood. 
The base of the prism should be about 2 cm, thick if the strips 
of glass are 4cm. long. The plates are warmed with a flame 
and the coloured balsam poured between them. After the 
balsam has cooled it is a good plan to run a quantity of melted 
sealing-wax upon the top of it, which strengthens the prism. An 
incandescent lamp or gas flame viewed through the prism is seen 
divided into a green and a red image, the former gradually 
fading away as the eye is moved towards the base of the prism. 
If a larger amount of the colouring matter be added to the 
balsam and the fluid be pressed out between pieces of plate 
glass, screens can be made which transmit a very good secondary 
yellow. Through these screens a sodium flame is absolutely 
invisible, though a gas flame appears of a colour very closely 
resembling the soda flame in tint. The colour of the trans- 
mitted light depends also on the original composition of the 
light. By a suitable adjustment of the dyes a screen can be 
made which appears red by lamplight and green by daylight, 
illustrating very well the peculiarity of the Alexandrite crystals. 
Johns Hopkins University, Baltimore. R. W. Woon. 
Sun-pillar and Parhelion. 
As the area over which such effects are visible is of some 
interest, it may be well to mention that a sun-pillar was visible 
in Dublin at 7 p.m. on Monday, April 28. It was preceded at 
6 p.m. by an unusually fine parhelion display, a portion of 
which was hidden from my view by houses. Two concentric 
circles and an inverted arc touching the inner one were visible, 
with a mock sun at the left hand end of the horizontal diameter 
of the inner circle, and probably another, hidden from me, on 
the right. The wind all the previous day had been cold from 
the north-east, in a fairly clear air, and still blew from about 
north. The sky was full of streamers and wisps of cirrus cloud. 
Doubtless a far more complete account can be given by other 
observers. GRENVILLE A. J. COLE. 
Royal College of Science, Dublin, April 30. 
A Rare Wild Sheep. 
SPORTSMEN and naturalists will be interested to learn that 
Mr. Talbot Clifton, who has recently been travelling in northern 
Siberia, has brought home from the valley of the Lena the skin 
and skull of a wild sheep of which no complete examples have 
hitherto been known in England. This sheep is the Ovzs bovealis 
of Severtzoff, a near ally of the bighorns of Kamchatka and 
Alaska. As it has no English name, it may well be known as 
Clifton’s bighorn. The skin is being mounted by Rowland 
Ward, Ltd., and will before long be exhibited to the Zoological 
Society. R. LYDEKKER. 
Beechen Hedges on Elevated Ground. 
IN your issue of April 10, Mr. Wm. Gee, of Buxton, ex- 
presses his surprise that some beechen hedges and smaller | 
trees in his neighbourhood have maintained their foliage through 
this winter, ‘‘ contrary to the habit of deciduous trees.” 
I beg to state that in Denmark, where beeches abound, these 
trees always behave in the same manner as those in Buxton did 
this year. An underwood of young beeches, densely covered 
with dry, brown, rattling foliage, is quite a characteristic feature 
of Danish woodland scenery. 
It would be most interesting to learn whether the beeches in 
NO. 1697, VOL. 66] 
NATURE 
[May 8, 1902 
England really used to throw off their leaves in autumn, and to 
ascertain the causes of such adifferent behaviour of the same 
species of tree in two countries of approximately the same 
climate. How this holding of the leaves could be a protective 
device to the individual young beech I cannot imagine; but 
to the whole underwood, or wood, this phenomenon might be 
protective, keeping out the cold winds of winter. 
18 V. Boulevard, Copenhagen. JuL. WULFF. 
IN reply to the interesting communication from Copenhagen 
anent the Buxton beeches, I would remind your correspondent 
that, as stated, the matured trees in the plantations hereabouts 
drop their leaves in the autumn as usual, the retention of them 
being observable only upon small young trees, and in the 
beechen hedges, and that this effect is not noticed, in this neigh- 
bourhood, for the first time. 
It may give colour to the suggestion that this holding of the 
past season’s leaves is an extra device under pressing circum- 
stances to remember that the tissue of such accessory organs as 
scales, bracts and stipules is of feebly conducting material, and 
that these dry beech leaves, acting as such, would also enclose a 
film of air which would tend to give fuller protection from the 
frosts which this winter have been uncommonly severe, the local 
observatory (in connection with Westminster) registering down 
to 3° Fahr. 
We have the highest authority for considering the beech as 
an unusually resourceful tree, as shown in its vernation, the 
growth of its bark and the care of its seeds ; and it would not 
be surprising to hear of its making a special defence against a 
special attack, and being successful as a ‘‘ survival of the fittest.” 
Barlbro’ Cottage, Buxton, April 28. Wo. GEE, 
CHEMICAL INSTRUCTION AND CHEMICAL 
INDUSTRIES IN GERMANY. 
N° 
more striking illustration of the position which 
Germany has won for herself in chemical tech- 
nology, and of the industrial preeminence which she has 
thereby secured in one of the most highly developed 
branches of the chemical arts, could have been given than 
that afforded by Prof. Witt in the lecture theatre of the 
Royal Institution on Friday evening, March 21 ; and to 
the observant eye no object-lesson could be more signifi- 
cant or more forcible than that presented by the remark- 
able series of chemical products, the outcome of the work 
of German manufacturers, which Prof. Witt had gathered 
together to point the moral of his discourse. 
In a few years we shall behold the extinction of one 
more agricultural industry, and the indigo plantations of 
India will have gone the way of the madder fields of 
Avignon. The death-knell of natural indigo has been 
sounded ; the planter may struggle on for a while in a 
futile effort to withstand the inevitable ; prejudice and 
trade customs may delay the fall of the fateful sword ; but 
the machinations of the German chemist, backed by the 
German capitalist, have slowly but surely compassed his 
ruin, and it is but a question of time when it will be 
accomplished. 
The conditions which have conduced to this result have 
been indicated, time and again, in these columns. But 
no more eloquent commentary on these causes could be 
adduced than is afforded by the report on chemical in- 
struction and chemical industries in Germany recently 
made to the Foreign Office by Dr. Frederick Rose, His 
Majesty’s Consul at Stuttgart, and which has recently 
been published.! 
This report deals with the facilities, and expenditure, for 
chemical instruction at the two Prussian Technical High 
Schools at Berlin and Hanover, and at the University of 
Berlin, and is supplementary to a report on chemical 
instruction and chemical industries in Germany already 
made public by the Foreign Office. 
The following brief analysis of this report will serve 
| to show by what methods the State has deliberately 
1 Diplomatic and Consular Reports, No. 573, Miscellaneous Series. 
