SCIENTIFIC SUMMARY. 
221 
astigmation can only be reduced within the necessary bounds by allowing 
the pencils transmitted obliquely through the lens to be brought to a focus 
nearer to it than can be done on a flat plate ; hence the attention of opticians 
is now being directed to the production of portrait-lenses for working on 
curved instead of flat-glass plates, the advantage of this arrangement being 
that a landscapist can thus obtain a small but exceedingly sharp picture 
with an instantaneous exposure, and that an enlarged print of great dimen- 
sions may be obtained from a very small negative of this class. 
Reproducing faded Prints. — At a recent meeting of the Photographic 
Society a successful method of reproducing faded photographs was com- 
municated by Mr. Pritchard. The faded print, having been first of all 
removed from its cardboard mount, is saturated with wax, so to render it 
more transparent. It is now superposed on a plate of glass coated with 
collodio-chloride of silver ; this coating is rendered more sensitive by being 
fumed with ammonia previous to exposure to the light. After being 
printed, the image on the glass plate is strengthened by being washed over 
wfith an intensifier composed of 
Gallic acid ... 75 grains 
Glacial acetic acid . . 2 drachms 
Acetate of lead ... 50 grains 
Distilled water ... 20 ounces. 
A little silver solution is added to this mixture where great intensity is 
required. By using this plate as a negative, prints may be obtained which 
are greatly superior to those from which the negative was produced. 
The late Rev. J. B. Reade, P.R.S. — As one of the earl) 7 photographic 
experimentalists, this gentleman was much esteemed. His death, which took 
place on December 12, removes from amongst us the last but one of the 
“ fathers of photography.” He was the first to employ gallic acid as a 
sensitiser in photography, and by its agency in connection with silvered 
paper he, in 1837, obtained enlarged views of minute objects by the agency 
of the solar microscope. He was also the first to publish the use of hypo- 
sulphite of soda as an agent for fixing photographs. 
Artificial Light for Photographic Enlargements. — Dr. Monckhoven has 
published the method by which he prepares magnesian blocks for producing 
an intensely actinic light by the oxy-hydrogen burner. His artificial 
magnesia is thus made : — Mix four pounds of English caustic, or calcined, 
magnesia with two pounds of carbonate of magnesia, add one pint of water, 
and knead them into a tough uniform dough. This dough is put into an 
appropriate box and pressed into a compact mass ; after which cut it in 
equal parallelopipedic pieces, and dry them for a few days in an oven, and 
afterwards make them red-hot for about half an hour. 
Preserving the Purity of Sensitive Paper. — The following method is recom- 
mended by an American writer, by which he says he can retain his sensitive 
paper for several days in good condition. To a bath composed of one ounce 
of silver to sixteen ounces of distilled water, he adds a few drops of liquor 
ammonise followed by an ounce of nitrate of ammonia. On this bath the 
paper is floated for one minute ; it is then drawn over the sharp edge of the 
dish for the purpose of removing all the surface solution, and is laid, face 
downward, on a quire of bibulous paper, covered by a couple of sheets of 
the same paper. Friction by the hand causes all the superfluous silver to 
