448 
POPULAR SCIENCE REVIEW. 
of some pliospliorescent substance, and then sensitising and exposing it to 
light in the usual way. A photograph thus taken is invisible in daylight, 
but in the dark becomes perceptible •, shining with a greenish or purplish 
phosphorescent light, which produces a very odd and mysterious effect. 
A New Doublet Lens. — Mr. Koss, the optician, has introduced a new in- 
stantaneous doublet lens at the suggestion of Mr. Stuart. Its equivalent focus 
is nearly 6|- inches, and the diameter of the lenses, which are equal, is about 
one inchj the distance between them is the same. It is fitted with a rotating 
plate containing four diaphragms, the largest of which is rather more than 
half, and the smallest about a quarter, of an inch in diameter. With the 
largest stop a circle four inches in diameter is covered sharply to the edge. 
It is spoken highly of by many of our best operators, and is becoming very 
popular for all kinds of work, views, portraits, &c. 
A Nev) Mode of Drying Plates. — Mr. Carey Lea has published in the 
Philadelphia Photographer 2 , new mode of drying plates for dry photography. 
Sulphuric acid is placed in a dish large enough to hold three times the 
quantity put into it. This being placed in a box, the dry plates are ranged 
round it in a frame. The dish used should be a glass or porcelain one, 
about three inches deep. The acid will augment in bulk by absorbing 
water ; when it attains about double its original bulk it should be replaced 
by fresh. 
A Curious New Photographic Toy, called the Kinescope, has made its 
appearance. It combines the principle of the stereoscope with that of the 
Zoetrope, and consists of microscopic photographs in a piece of apparatus 
in general appearance resembling a Stanhope lens. It forms an elliptical 
medallion with two photo-microscopic cylinders in the centre, perpen- 
dicular to the thickness of the medallion. The object appears in two 
phases of motion, and the effect of moving is suggested by a rapid change 
produced by a guide about the cylinders, which are siuTounded by a caout- 
chouc membrane, on which is a v^ertical rod terminating in a button outside 
the medallion. Putting the eye to the central aperture, you see only one of 
the images, and then, by pressing the button, the pictures are changed so 
rapidly, that the second image takes the place of the first before the im- 
pression made by the former has disappeared. 
. A New Developer. — Mr. Carey Lea, in the British Journal of Photography, 
states that he has discovered a new substance capable of developing the 
latent image. This is hcsmatoylin, a substance which, after undergoing 
certain changes, becomes — although in itself almost white — the colouring 
niatter of logwood. A solution of this, with a little acetic acid to keep its 
action under control, forms a very good developer — in some respects re- 
sembling the old pyrogallic developer. 
A Substitute for Grotmd Glass. — Mr. Walter Woodbury has suggested the 
use of gelatine, rendered partially opaque by mixture with some white 
pigment such as oxide of zinc, to take the place of ground glass in backing 
up transparencies. The effect obtained is certainly superior to that given 
by the ground glass. 
The Great Solar Eclipse. — Photographers went out from England, India, 
France, and Prussia, to photograph the. solar eclipse of 1868, the greatest 
which has taken place for four thousand years. News have been received 
