100 
MAGAZINE OF SCIENCE ANI) ART. 
worst female ward, a portrait hung up for eighteen 
months had never been touched by any of the patients. 
I think this will he considered as a very important ap¬ 
plication of the art, because it seeins to me that a point 
is gained in the treatment of violent patients, by finding 
only one object which they will refrain from destroying,, 
which may result in the care of many who would 
otherwise have remained hopeless maniacs. 
I may here call vour attention to a few of the prac¬ 
tical uses of the art It is used by the Manchester 
print designers to aid them in producing new patterns 
for calicos. 
In Greenwich Observatory' all the magnetic instru¬ 
ments, including the vertical, horizontal, and declination 
magnets, and the barometer and wet and dry huib 
thermometers, register their own fluctuations with 
degree of accuracy not to be surpassed, on paper ren¬ 
dered sensitive to artificial light, which is afterwards 
developed; and positives, being taken from these, are 
distributed to the observatories in different parts of the 
world, which are thus put in possession of fac-simile 
observations, • 
Another very interesting application of the art is, as 
an assistant to the law, both criminally and civilly, 
criminally, in taking the portraits of thieves and other 
malfactors, which are exchanged between the various 
jails, so that a man whose identity there would other¬ 
wise have been considerable difficulty in establishing, 
is thus positively recognized, and the punishment of the 
criminal is rendered more certain ; civilly, in taking 
views of houses, &c., to be produced as witnesses, in 
place of drawings, in cases of disputed property. In 
stances of both of these uses of the art have come under 
my own notice. 
Having thus rapidly brought in view* before you the 
principal events in the history of Photography, I pro¬ 
ceed to show you the practical details of the waxed 
paper process, for which 1 claim the following advan¬ 
tages. An almost absolute freedom from failure, great 
portability, and, above all, the property of keeping the 
excited paper sensitive for a lengthened period. The 
paper to be used should be selected of a fine smooth 
grain; I prefer Canson’s negative paper to any other, 
as producing better half tones. I should strongly re¬ 
commend that amateurs save themselves all the trouble 
and annoyance incidental to waxing and iodizing the 
paper, as it is now an article of commerce, and can be 
procured of a superior quality to that which is home 
made (a specimen was here shewn) ; it will keep good j 
when iodized for several yearn ; it must never bo 
touched with the fingers, because when developed there 
would be visible a very correct but exceedingly annoy¬ 
ing photograph of every line, almost of every pore of 
the skin. 
The sensitizing bath is made of the following chy- 
micals, in these proportions distil led water, 6 oz., 
nitrate of silver, 210 grains, glacial acetic acid, 4 drams, 
alcohol, 6 drams. Animal charcoal most always be 
kept in the bottle. This bath must invariably he filtered 
before using; it will keep any length of time in the 
dark. ('This, by which these negatives were prepared, 
had been mixed eighteen months.) For sensitizing, flat 
dishes of Wedgwood ware, rather larger than the paper 
to be used, are required—I always use three. Now, it 
is essential that these he washed with the greatest care ; 
I use first hot, then cold, and lastly distilled water; 
the cloths must be linen, never washed with soap, and 
should one of them fall on the floor, reject it. I always 
finish oft' with a small piece of cotton wool ; never al¬ 
low the fingers to touch the inside of the bath. I am 
thus tedious in the minutia?, because I am convinced, 
from 14 years experience, that want of attention to 
these details, is the principal reason of the non-success 
of many amateurs. The filtered bath is then gently 
poured into the dish, so as to avoid the formation of air 
bubbles, and the paper, held between whalebone forceps, 
is floated carefully on the solution ; in laying it down, 
commence at the middle, to prevent air underneath it; 
as soon as it is floated, take it up, turn it over, and lay 
it down on the other side; then, by gently agitating the 
bath, and holding the paper down in the solution, the 
sensitizing proceeds equally over the whole sheet. The 
paper should bo turned every minute, until it assumes 
a beautiful straw color, it is'then thoroughly sensitized, 
when the thermometer ranges from 00 to 70 degrees of 
Farenheit—this is effected in about five minutes; it is 
then removed into a bath, containing clean water, which 
is the second of the three dishes; in this, the paper 
must be turned over constantly, for three minutes, when 
the soluble nitrate of silver which is in excess, will have 
been removed. If the^ paper is to bo kept a very long 
time before exposure, it is necessary to remove it into 
another bath pf water, and treat it as before. A sheet 
of stout blotting paper is laid out, the sensitive paper 
laid carefully down, and the superfluous moisture re¬ 
moved; the paper cau now be placed in the double 
frame, or preserved iu a fresh sheet of bibulous paj>er ; 
none of this paper should be used twice. The paper 
prepared after tins formula, will retain its sensitiveness, 
if the weather is not too warm, for three weeks; it is 
preserved much better if air is excluded—(a case made 
for this purpose was here exhibited and explained). 
The time of exposnre varies so much, that I can hardly 
attempt to give any rule; however, I may mention 
that the view of the Royal Exchange was taken with a 
31 inch lense, and a one inch stop, in a quarter of an 
hour, between 11 and 12 o’clock, on the 21tfi of Mav. 
These of the University, with a § inch stop, in half an 
hour—the exact time can only be arrived at by expe¬ 
rience; of course the amount of yellow ligbt in the 
atmosphere varies the time of exposure. I have found 
that I can work in this country in the winter much 
quicker, than at a corresponding period of the year in 
England. I think the intense heat of the summer 
would not be favourable for the production of good 
pictures. The camera is now so well known as not to 
require any explanation in this papor ; not so this roll¬ 
ing slide, an account of which, with drawings, I extract 
from the Journal of the Pliotograpliic Society, April 
21st, 185C:— ’ 
The object of the slide is to enable a person to carry 
out any number of sheets ef sensitive paper, and change 
them conveniently in the open light. The slide is 
fitted up until two rollers, a a ; and the sensitive sheets, 
b b, are gummed together, making one long hand, the 
ends of which are "u mined together to pieces of paper 
I always kept on the rollers; the sensitive sheets are 
wound off the left or reserve roller on the right or ex¬ 
posed roller, until all are exposed. The rollers are 
supported on springs a a, to render their motion equal; 
they are turned by the milled heads m m, and clamped 
when each fresh sheet is brought into position by the 
nuts aa* ; c is a board which is pressed forward 
by springs c> C|, so as to hold the sheet to be exposed, 
and keep it smooth against the sheet of glass d ; when 
the sheet has been exposed, the board is drawn back 
from tbe glass in older to release the exposed sheet, and 
allow it to be rolled on the exposed roller; the board 
is kept back whilst this is done, bv turning the square 
rod c* half round, so that the angles of tbe square will 
not pass back through the square opening until again 
turned opposite to it; e e are doors by opening which 
the operator can see through the yellow glass v y, to 
adjust the position of the sensitive papers when chang¬ 
ing them. The sheets need not be gummed together 
with any particular care, the pressure board insures 
their being kept flat and even whilst being exposed; 
alL that is necessary is, that the person joining them 
should have clean hands and lay tlie sheets to be con¬ 
nected on clean paper. It takes about an hour to fix 
3G sheets on the rollers; it takes less than a minute to 
change each sheet. I have taken a great many views 
with this'apparatus and can strongly recommend it. 
Supposing the sensitive paper to have been exposed, 
the next process is to develope the latent picture. On 
removing the paper from the double frame, perhaps a 
faint trace of the picture may be visible, indeed I 
always like to see something on the paper, this must 
