1874.| Technology. BAT 
very nearly unity, the angle of 45° is very near the Brewsterian incidence. 
The instrument has been further modified by Janssen. 
Microscopy.—Herr Moller has introduced a very ingenious modification of 
his celebrated Diatomaceen typenplatte ; the old form had about four hundred 
species neatly arranged in the space of about a quarter of an inch square, each 
slide being accompanied by a manuscript catalogue. The new arrangement 
consists of a photograph about 4 millimetres square, of eighty circles, ten in 
a longitudinal and eight in a vertical direGtion; beneath each circle is the 
name of the object and its author, and in the centre of each of these circles 
is a diatom, and in many cases two are mounted in order to show front and 
side views. The whole collection independently of its great value to the 
student of Diatomacez is a marvel of manipulative skill. 
Those who have attempted to dry the petals of Tvadescantia Virginica, have 
probably noticed that the coloured cell contents break from their envelopes 
and flow towards the margin of the petals, leaving the greater part in a 
colourless condition. The petals and their alcoholic tin@ure giving an 
interesting absorption spectrum of three bands, it has been a desideratum to 
preserve the colouring matter in some permanent form for purposes of 
reference and comparison; the alcoholic tinctures of most flowers rapidly fade, 
and it is impossible to dry the very fleshy petals of Tvadescantia in the ordinary 
way ; but the colour has been successfully preserved by mounting in balsam 
by the ‘‘ Oil of Cloves’? process. The petals separated carefully from the 
flower so as to avoid breakage or bruises are immersed in ordinary methylated 
spirit and placed under the receiver of an air pump to ensure rapid displace- 
ment of the contained fluid and air; they are next transferred to absolute 
alcohol, the air pump being also used to save time, then placed in oil of cloves 
until transparent, and can then be mounted in balsam, taking care that as little 
heat as possible is employed. Petals of Cineraria and Lobelia speciosa also 
make good objects for the micro-spectroscope. The colours are much more 
brilliant than when dried petals are mounted in balsam, even in those plants 
which can be successfully dried by the ordinary process. 
An exhibition of high scientific value took place at the meeting of the 
South London Microscopical and Natural History Club. This society has 
increased so much during the three years of its career that it has been found 
necessary to seek for a larger meeting-room, in which the first meeting was 
held on the 21st July. Instead of an indiscriminate collection of obje&s being 
exhibited, as at most conversaziones, the President, Dr. Braithwaite, F.L.S., 
determined to limit the exhibition to three subjects, viz., the cuticle of plants 
and its appendages of hairs, scales, glands, &c.; cyclosis or circulation in 
plants ; and the hard tissues of fruits. A very complete series of preparations 
was shown, and in addition short lectures on each*subje@& were delivered by 
the President and two other demonstrators conversant with their respective 
departments. The educational success of the exhibition was so marked that 
other meetings illustrating equally important points of minute structure will 
follow, and probably replace the old fashioned and almost useless soiree, 
which has hitherto been the only means of bringing the microscope and the 
minute structure revealed by its aid before the general public. 
Dr. J. G. Richardson exhibited at the Academy of Natural Sciences of 
Philadelphia a new “Syphon Slide.” It consists of a slip of plate glass 
3 inches x 1 inch or other convenient size, in the upper surface of which is 
ground a shallow groove, elliptical both in its transverse and longitudinal 
section, and deeper towards one end than the other. This excavation is 
arranged so as to receive a small living fish, tadpole or other aquatic animal, 
and retain it under sufficient constraint to prevent any troublesome move- 
ments, and also to prevent any injurious pressure. The improvement over 
other slides of this description consists of imbedding a small metallic tube 
at each end of the cell, and adapting to each of these two tubes pieces of 
elastic pipe, one being intended for the entrance and the other for the exit of 
any fluid which it might be desirable to employ. For the examination of 
