132 
POPULAE SCIENCE EEVIEW. 
ently affected by the two different modes of illumination, and that, therefore, 
the usual law might not hold good ; asserting that from spectra experiments 
he had made, he was confident some such minute difference had existence. 
Some years ago, M. Claudet called attention to a difference between the 
visual and the actinic focus observed in connection with an ordinary compound 
photographic lens, the changes varying with different portions of the same 
day. Dr. Maddox agrees with his friend the editor, but believes that other 
causes intervene ; because, whatever the position of the lens, it is still the 
same, whether that position projects before or beyond the visual focus. 
Another difference observed by Dr. Maddox is one which we think might 
reasonably be looked for, viz., the difference in the effects produced by certain 
colours photographed by artificial light and those photographed by natural 
light. A few experiments in this direction might be valuable to those who 
are engaged in copying paintings, a very important and promising branch of 
the art-science. Professor Piazzi Smyth is said to be experimenting in this 
direction. 
But if the new magnesium light fail in producing specimens of micro- 
photographs, the very cause of that failure is in other departments of the art 
a positive gain. We have seen many portraits taken with its aid, which 
were softer, rounder, and far more truthful in their rendering of texture and 
general effect, than were similar portraits taken in daylight. To facilitate 
the use of this light in the hands of photographers, Messrs. Solomon & Co. of 
Red Lion Square, have introduced a lamp in which it can be very conve- 
niently and effectively burned. This is the invention of Mr. Alonzo G. Grant, 
an American gentleman residing at Nottingham. The wire is wound on 
spools, and is drawn between cylinders and through a tube by a clock-work 
arrangement under immediate control, so that it continues to be pushed 
forward, or not, according to the will of the operator. In order that the 
light may be continuous, two separate wires are burnt, so that should the 
flame of one, from accident, be extinguished, that of the other would imme- 
diately re-light it. A parabolic reflector is used behind the flame to strengthen 
and direct the light. The instrument is very complete, and, we beheve, 
economical. 
The Carbon Process. — A paper on photographic painting in carbon was 
read before a recent meeting of the Edinburgh Photographic Society, by Mr. 
W. H. Davies, a talented photographic amateur, who has experimentalized 
in this direction for the last four years. The process described was very 
similar to that detailed in our last, and several members of the society spoke 
of specimens produced by it which they had examined long previous to the 
announcement of Mr. Swan’s patented process. 
A New Ophthalmoscope for Photographing the Internal Surface of the Eye . — 
This interesting instrument was described by Mr. A. M. Rosenburgh in a 
paper read before the Canadian Institute, and is thus described : — Two brass 
tubes, I-| inch in diameter, respectively 4 and 2^ inches long, are fitted to 
the aperture of a small camera, so that they move freely in a collar of brass, 
and the shorter tube is turned towards the light. A double convex lens is 
placed at the inner extremity of the illuminating tube, and as close as pos- 
sible to its juncture with the camera tube, being 1 j inch in diameter, and 
having a focal distance of 2| inches. The camera is 3 inches square and 7 
