DECEMBER 27, 1906 | 
NATURE 
sures of a happy home and world-wide reputation, 
while we are conscious of a genuine admiration for 
the firm resolve to ‘‘ make the most of his time’’ and 
to keep perpetually before him the remembrance of 
“how injurious megalomania may be for a student.” 
EVan EL. 
Illustriertes Handbuch der Laubholzkunde. By C. K. 
Schneider. Pts. iii. and v. (Jena: Gustav Fischer, 
1906.) Price 4 marks each. 
Tue general plan of this handbook on trees cultivated 
in Europe was explained in the notice of the first two 
parts that appeared in Nature, November 24, 1904. 
The third part was issued early last year, and the 
fifth part—somewhat enlarged—completes the first 
volume. 
The third part contains the final portion of the 
Berberidaceze, the orders Menispermaceze to Crassu- 
lace, and part of the Saxifragacee, the largest 
genera being Berberis, Mahonia, Magnolia, and Ribes. 
The Drupacee and Pomacez, generally regarded as 
suborders of the Rosaceze, here treated as orders, form 
the subject of the fifth part. Prunus, Padus, Pyrus, 
Sorbus, and Crategus are large and difficult genera. 
It becomes more apparent that Dr. Schneider 
favours subdivision, for, in addition to the suborders 
mentioned, subgenera such as Chenomelei are raised 
to generic rank, and some of the species would cer- 
tainly be regarded by other authorities as varieties; 
also it is noticeable that the author does not confine 
himself to trees in cultivation. The bool thus be- 
comes more of a dictionary and less of a practical 
manual; but due credit must be given to the author 
for the enormous amount of energy expended, and 
for the searching and critical investigation of speci- 
mens that has been accomplished. The advantage of 
the rules laid down at Vienna last year becomes evi- 
dent from the list of changes noted in the supplement. 
Old-fashioned Flowers and other Open-air Essays. 
By Maurice Maeterlinck. Translated by A. 
Teixeira de Mattos. With illustrations by G. S. 
Elgood. Pp. vii+115. (London: George Allen, 
1906.) Price 3s. 6d. net. ; 
PuBLisHErRsS have to cater for readers of various tastes, 
and so we suppose there are some to whom the pre- 
sent little book will appeal. For ourselves we can 
but wonder that anybody thought it worth translating. 
The text is mostly purely rhapsodical, reminding us 
of Ruskin at his worst. There is very little said about 
flowers as flowers, and the moral and philosophical 
reflections present no striking novelty. The illustra- 
tions are attractive but over-coloured, and probably 
do not do justice to the artist’s original drawings. — 
LETIORS LO PHE EDITOR. 
[The Editor does not hold himself responsible for opinions 
expressed by his correspondents. Neither can he undertake 
to return, or to correspond with the writers of, rejected 
manuscripts intended for this or any other part of Nature. 
No nolice is taken of anonymous communications.] 
The January Meteors. 
Tue January meteors are seldom visible in England under 
favourable aspects, the weather being often adverse at this 
season. Moonlight will partly veil the display in 1907 
and the best times to look for it will be on the venir 
of January 3, and 4 during the two or three hours pre- 
ceding moonrise. 
pase shower is sometimes as rich as an ordinary return 
of Perseids, and it always furnishes some bright, long 
NONLOZO; VOL, 754] 
199 
meteors of an unusually conspicuous character. We have 
gathered a large number of double observations of Perseids 
and Leonids, and know their average heights very well, 
but very few real paths of the January Bootids (or Quad- 
rantids) have ever been computed. It is desirable, there- 
fore, that observers who are fortunate enough to notice 
any members of the latter shower should record their 
apparent paths with the greatest accuracy which the 
circumstances allow, with the view of finding their heights 
and radiants. 
The position of the radiant point has been already well 
determined at 230°+53°, and it is not probable that we 
shall ascertain it more precisely until photography can 
effectively take the place of the eye in meteoric observation. 
= W. F. DENNING. 
Stereoscopic Lantern Slides. 
PROBABLY many people who have taken interest in stereo- 
scopic photography at one time or another have regretted 
that there should be no simple means for showing the 
effect to a large audience. 
As a matter of fact, this can be done very easily in either 
of two ways. A stereoscopic lantern slide is first made 
by photographing an ordinary stereoscopic pair of pictures. 
This pair of pictures is then projected upon the screen 
with an ordinary lantern. The stereoscopic effect is 
obtained by using either a mirror stereoscope or a prism 
stereoscope. The former consists of two small pieces of 
mirror held one in front of each eye. The observer has 
the screen, not in front of him, but on one side, say about 
60° from the direction in which he is facing. 
In each mirror the pair of pictures is seen, and by tilt- 
ing one mirror with respect to the other, so that the two 
outside images are superposed, the picture suddenly leaps 
into relief. Of course, if the wrong pair be superposed the 
familiar inverted relief will appear. It is easy to mount 
the mirrors in a sort of spectacle frame, one of them 
being fixed and the other capable of rotation about a 
vertical axis. 
It would not be difficult to explain to an audience of 
average intelligence the method of using such spectacles ; 
the spectacles could be made at a very small cost, and the 
beauty of the effect would appeal to many. 
Cases frequently arise in university lectures in which a 
stereoscopic presentation of slides would greatly simplify 
explanations, e.g. in biology. 
The other method is to use a single small achromatic 
prism, which is held in front of one eye, the refracting 
angle being vertical and directed towards the other eye. 
Of course, prisms of different angles are required for 
different distances, but a single prism can be made to 
suffice for a large range by twisting it about a vertical 
axis, without greatly impairing the ‘‘ stereoscopism.”’ 
At first sight one might think that the effect could only 
be seen by observers situate in or near a plane bisecting 
the screen at right angles, but this is not the case. 
Indeed, anyone who has worked with stereoscopic photo- 
graphs must have been struck with the ease with which 
the eyes will adiust themselves to pictures which are not 
correctly aligned, and experiment also shows that the two 
pictures need not be of the same size. 
G. A. SHAKESPEAR. 
The University, Birmingham. December 17. 
Emerald Green Sky Colour. 
Wume on a short stay at St. Moritz I was much struck 
by the peculiar colour of the sky on the evening of 
December 10. It had been threatening snow most of the 
day, and a few flakes fell during the afternoon, the sky 
being overcast. At about 3.30 p.m. to 4 p.m. the sky 
cleared over the mountains towards the east, and revealed, 
instead of the usual blue, a fairly large expanse of vivid 
emerald green. None of us had ever seen it before, so that 
we all stopped. I should be much pleased if any of the 
readers of Nature could give me some idea of the cause 
of this unusual phenomenon. J. W. Nosve. 
Kurhaus Lenzerheide, St. Moritz, December 18. 
