SCIENTIFIC SUMMARY. 
103 
by substituting for the lime, in tbe former of these sources of illumination, 
a piece of carbonate of magnesia, or, more strictly speaking, a mixture of 
carbonate and chloride of magnesia. The mechanical and even the gaseous 
portion of the lime light remain as they are ; the only modification required 
to render the oxy hydrogen light thoroughly useful for photographers being 
the substitution of the magnesia as above described. 
In less than three minutes Dr. Monckhoven produced an enlargement on 
a sheet of paper from a carte negative ; and with an exposure of only six 
seconds he was enabled to impress a wet collodion plate so as to yield a 
good picture. Although this light is not more powerful than that produced 
by the combustion of magnesium ribband or wire, it is so actinic when com- 
pared with the lime light that its introduction will not fail to give an im- 
mense impetus to the production of life-size photographs by the magic 
lantern, or as photographers now designate it, the enlarging apparatus. 
Partial Intensification of Negatives. — A process by which negatives slightly 
over exposed and deficient in general intensity may be so improved as to 
yield good proofs has been published by Herr Meissner. The treatment is 
one that in the hands of an artist of taste is susceptible of yielding some 
excellent effects. After fixing with cyanide of potassium the negative is 
varnished. Those parts, such as the whites, that do not require strengthen- 
ing are carefully painted over with a solution of gum arabic, to which any 
convenient colouring matter is added so as to permit every touch to be seen. 
Thus prepared the plate is placed in a vessel of methylated spirits of wine, 
by which the varnish is removed from those portions not protected by the 
gum arabic ; and after the plate is washed it is intensified in the usual way, 
the whites being protected from the action of the intensifier by the coating 
of varnish. In this way may be obtained very artistic effects. After the 
intensification has been completed the plate must be varnished. 
Hmo the Eclipse of the Sun was Photographed. — Some very superior nega- 
tives of the last solar eclipse were obtained by a party of American photo- 
graphers, who operated with the large equatorial telescope of the United 
States Naval Academy, Annapolis. This instrument has an object- glass seven 
and three quarter inches clear aperture, and nine and a half feet focal length. 
It was fitted with a camera capable of taking plates seven inches square. 
On these were thrown (the eye-piece of the telescope being also used) images 
of the sun four inches in diameter. The camera was fitted with an instanta- 
neous shutter capable of being acted upon by a hair trigger. One hundred 
and twenty-two negatives were obtained. Seven negative baths were em- 
ployed. The duty of one operator was to coat the plates with collodion and 
immerse them in the bath ; another took each plate out, wiped its back, put 
it into the plate holders (of which there were several) and passed it out to a 
third operator, who placed it in the camera, adjusted the telescope and 
exposed, noting the time by a chronometer placed at his elbow, and then 
returning it to a fourth operator inside, whose duty was to develop the 
image and number the plates with a diamond. By this even distribution of 
labour, and by the help of every necessary kind of mechanical appliance, 
negatives were taken at the rate of one every minute of the eclipse, or a 
hundred and twenty-two altogether. The chemicals used were of the usual 
kind ; the collodion contained cadmium and ammonium j the negative bath 
