SCIENTIFIC SUMMARY. 
215 
A Scale for the Microspectroscope. — The February number of the Monthly 
Microscopical Journal describes a plan of estimating the position of absorp- 
tion bands which is likely to supersede all others hitherto employed. The 
plan consists in throwing, by lateral illumination, a bright line (a beam from 
a lamp, sent through a line photographed on a glass plate, the rays being 
rendered parallel by a lens) upon the spectrum. By means of a micrometer 
screw the line may be made to travel over the whole of the spectrum, and 
thus the exact position may be read off in numbers of the screw. 
Nature of the so-called Brownian Movements of Microscopic Particles. — Pro- 
fessor W. Stanley Jevons read an interesting paper on this subject before 
the Philosophical Society of Manchester on January 25. The paper is 
too long for abstract, but we may quote the following passage as indicating 
the author’s views : — I consider it to be established experimentally that the 
microscopic movement is due to electric action, and if I may venture to 
suggest a somewhat speculative explanation of the action, I would point to 
the experiments of M. Wiedemann on electric osmose. It was first observed 
by Mr. Porret that when the poles of a battery are placed in two portions of 
water separated by a porous division, not only is some of the water decom- 
posed, but another and far larger portion is impelled towards the negative 
pole. M. Wiedemann having exactly investigated the phenomenon, found 
that for one part of water decomposed 5,000 parts were transported through 
the porous septum. This impulsion is greater as the resistance of the liquid 
is greater, and ceases altogether when sufficient acid or salt is added to 
render it a good conductor. Every particle which is thrown into a polar 
condition by the action of water must be capable in a minute degree of 
exerting a similar force. In ordinary osmose the particles being fixed cause 
a transportation of the fluid \ in microscopic movement, on the other hand, 
the particle is free to move, and the reaction of the liquid probably produces 
those movements which are visible in the microscope. 
PHOTOGRAPHY. 
The Possibility of obtaining Heliochromes. — Mr. Glaisher, the President of 
the Photographic Society, having at a recent meeting of that body stated it 
to be his opinion that the laws of light would require to be changed before 
photographs in their natural colours could be obtained, has had this dictum 
controverted by several authorities on this subject. Among others, the 
Rev. J. B. Reade says that it is because the laws of light are what they are 
that they have the best chance of succeeding in obtaining heliochromes. 
The editor of a photographic contemporary considers that it is somewhat 
singular that the President of the Photographic Society should be un- 
acquainted with the fact that, even without any change in the laws of light, 
heliochromy is an accomplished fact. The difficulties attending upon their 
production and the sombreness of their hues interpose obstacles to their 
being generally introduced, but the scientific possibility of their production 
has been both proved and demonstrated. He describes the method bv 
which was obtained a photograph (in colours) of the solar spectrum that 
