SCIENTIFIC SUMMARY. 
21 ? 
in lead or other soft metal by heavy pressure, and this metallic impression is 
used as a mould for the production of copperplates by electro-deposition. 
The editor of the British Journal of Photography has been holding up to 
ridicule the Times fine-art critic, who, in writing about certain photographic 
productions of Colonel Stuart Wortley, has supposed that because they were 
intended to resemble moonlight effects they were really obtained by the 
agency of moonlight. He assumes that it would be desirable, if not necessary, 
that art critics should make themselves acquainted with the principles of 
the methods by which pictures are produced, by which they will avoid such 
blunders as those referred to. As the method of producing the so-called 
moonlight photographs has never been published in the Popular Science 
Review, it may not be out of place here to publish this supposed secret. In 
selecting the subject let it be, if at all possible, an aquatic one ; no other 
answers nearly so well. The view must be illuminated by strong sunshine, 
and, unlike the usual method of taking an ordinary picture, the camera must 
be directed towards the quarter from which the sun is shining. The expo- 
sure must be as nearly instantaneous as possible. If the vertical angle of 
the picture be such as to include the sun, so much the better ; but as the 
powerful luminousness of the sun will cause such an amount of optical natation 
as will entirely destroy the pictorial effect, it is necessary that means to pre- 
vent this be had recourse to. One of the simplest, and probably the best, is to 
put a piece of wet red blotting-paper on the back of the glass plate on which 
the sensitive film reposes. It is necessary that it be in optical contact, and 
this is secured by the simple expedient of making the paper quite wet before 
applying it to the back of the glass plate. When such a precaution as this 
has not been taken, the photograph of the sun presents a very peculiar 
aspect, being surrounded with concentric rings. When a print is taken from 
a negative obtained in this manner the effect is precisely that of moon- 
light. 
Photographing Criminals. — The Home Secretary has been sending intima- 
tions to the authorities of several of the larger towns requesting them to 
take photographs of prisoners and furnish copies to the central authorities 
in London. It is to be presumed that the central album will have suitable 
divisions for the respective class of occupants, so that thieves, burglars, 
murderers, forgers, &c., may be retained in their appropriate places. 
PHYSICS. 
Application of Optics to Chemistry. — At one of the February meetings of 
the Royal Irish Academy, Professor Jellet communicated an important paper 
on the above subject. Having made some general preliminary remarks 
respecting the changes in rotation observed under the polariscope as the 
result of the action of acids on bases, he proceeded to the consideration of the 
changes effected by the action of nitric acid on quinia. From his investiga- 
tions he was able to establish the existence of an acid nitrate, or binitrate, 
of that base— a salt which has not as yet been isolated. He promised to make 
a further communication on the combinations of nitric acid with a mixture 
of quinia and ammonia. 
