The Sun.
London, England, 1839-09-02 00:00:00

THE DAGUERRE SECRET•

At the weekly sitting of the Academy of Sciences of
Paris, on Monday week, the process of M. Daguerre,
for the formation of photogenic drawings, was, as had
been previously announced, communicated to the public.
From an early hour all the seats allotted to the public
were occupied, and upwards of 200 persons disappointed
of gaining admission, were stationed in a crowd in a court
of the Institute, and formed a kind of scientific enzeute.
Every body was anxious to hear the secret, every body
to catch the vzot ; all were desirous of learning whether
their own scientific conjectures would be confirmed
or not. _ _ _ .

At three o'clock M. Arago commenced his explana-
tiou. We shall not attempt to follow the great savant
through the details of his long statement, a large pro-
portion of which related to the history of the discovery
—a subject already pretty well known to the public ;
• and we shall only mention so much of that part of it as
s belongs to MM. Niepce and Daguerre.
/ The late M. Niepce, M. Arago proceeded to state,
appeared to have commenced his photographic experi-
ments in 1814. His first connection with M. Daguerre
commenced in 1824, when, through information received
from an optician at Paris, he learned that this gentle-
man was engaged in an independent series of photo-
genic researches, and especially in trying to fix the
images of the camera obscure: They associated their
labours in 1829. It is proved that for the photographic
copying of engravings, and for the formation of plates
fOr engrave a, in an advanced state of preparatory
' sketching of the subject, this gentleman was, in
1826, possessed of the secret of making shades corres-
pond to shades, light parts to lights, demi-tints to demi-
tints, Sze.; and that he also knew how to make his
drawings so produced insensible to the ulterior action of
light. The sct of partnership, drawn up between M.
Niepce and M. Daguerre, and which afterwards stood
good between his son and the latter gentleman, states
thet some entirely new methods had been discovered by
M. Daguerre, and that they had the advantage of being
able to reproduce images from sixty to eighty times
more rapidly than by the processes previously adopted.
It appears that M. Niepce, in his own photographic
researches, had first made use of a sheet of silver covered
with the purest bitumen (called, in France, Bitume de
Judee), which had previously been dissolved in oil of
lavender. He used to beat this sheet of silver till the oil
was completely evaporated, and only a kind of whitish
powder remained adhering to the surface. He then
placed the sheets so prepared in the focus of the camera
obscura, and obtained the image of the object ; but
the trace was hardly visible. To obviate the imperfec-
tion, M. Niepce next thought of plunging the sheet,
when reteoved from the camera obscura, into a mixture
el oil of lavender and oil of petroleum—a method that
suceeded, and augured still further improvement ; for the
image became visible like an ordieary engraving, and on
wasting the sheet with distilled water left the representa•
lien permanent. As a further improvement •of this,
M. Niepce used a new mixture of sulphuret of potassum
and iodide, but the light acted very slowly upon it, and
the iodine, spreading itself over the surfac,, rendered
the image confused and chscure. The oil of petroleum,
-first used by tips- gentleman, was found to have the pro-
perty of attaching those points of the metallic surface
which had l,een preserved front the action of light by the
shales, while it was of no effect on those parts touched by
the solar ray s.
It w Is at this stage of the invention that M. Da-
gucrre's I.thours were joined to those of M. Niel ee ;
end rt is only fter a long series of experiments, carried
' on with utyvearicrl perseverance for many years, that
after M. Nicpcc's death, M. Daguerre has at length
resolved the problem to its present extent. We omit
the history of these experiments, and pass on at once
to the actual process as now used by its author.
• A sheet of copper, phitcd with silver, is washed care-
fithy in a sohation of nitric acid. which removes from it all
the extraneous matters on its surface, and especially
any traces of copper from the silver surface. A
sight degree of friction is rseptishe in this process,
but it mu,t not he applied alwa in the 'same
tlrection. M. Daguerre has observed, that with the
friction used ha a particular manner, a shc.l of copper
thus plated with silver answered better than a sheet of
silver alone ; an:l he inters from this, that voltaic agency
is not unconnected with the cif,:tct. When the sheet is
thus prepared, it is placed in a closed box, and exposed
to the vapour of iodine. This vapour is made to pass
through a very fire sheet of gauze, to render its distri-.
bution more eqaable over the suface of the silver ; and
in order to effect this object (which is quite indispen-
sable) more certainly, the sheet has a small metallic
rim raised round all its edges. A thin coating, of a
yellow colour, is thus formed on the surface of the sheet,
which is estimated by M. Dumas at not more than the
millionth part 01 a millimetre in thickness. The sheet,
when covered with this substance, is of the most ex-
cessive sensibility to light, and is thus ready for the
camera obscura. M. .Dagucrra, in the instrument
which he uses, employs a piece of unpolished glass,
which he brings first et all into the focus of the lens, in
order to determine the exact point at which the sheet
should be placed ; and, as soon as this is determined, the
sheet is placed accordingly. A few seconds, or minutes,
according to vhe time of day, the state of the atmos-
phere, &e., suffice for forming the photogenic image ;
but it is hardly, if at ail visible on the surface of the
sheet. To make it so, the sheet is placed in another
box, and exposed to he vapour of mercury, heated
to 60 degrees Reanaur, or 167 degrees of Fahrenheit.
One of the most curious circumstances attending this
part of the process is, that the mercury must act
at a certain angle. If the drawing is intended to be
seen vertically, it must be suspended over the mercury
at an angle of 45 degrees ; if it is to be seen at an angle
of 45 degrees it must be suspended horizontally. Ou
being taken out from the mercury bath, the sheet is
plunged into another bath of the hyposulphite of soda ;
this solution attacking the parts upon which the light
has not been able to act, and respecting the light parts
—being the very inverse of the action of the mercury.
It may be supposed, therefore, observed M. Arago,
that the light parts of the image are formed by an
amalgamation of mercury and silver, and the dark parts
by a sulphuret of silver, at the expense of the hypo-
sulphite of soda. M. Arago observed that no satisfac-
tory reason had yet been given for this latter part of the
process. The sheet is finally washed in distilled water,
and the operation is terminated.
The drawing, thus obtained, is perfectly irsensible to
the action of light, but it is liable to injury, just like a
crayon or pencil drawing, and requires to be presered
under a glass. The effect of the who',e is miraculous ;
and as an instance, we may mention that one of the
(leavvings exhibited by M. Daguerre, on Monday, was
'the view of a room with some rich pieces of carpet in
it ; the threads of the carpet were given with mathe-
atied accuracy, and with a richness of effect that
was quite marvellous.
Such is the process
of Da nerve ;we must add,
that it is found that the sun-light does not act equally
• well at all hours
at equal heights the day, nor even when the sun is
abooftvee the horizon. Thus the effect is
produced better at
the after von ; and hennclenthtleeDmorning than at two in
immense value in measuring the e gbuintensityerrot yopfe
img be of
,• The camera obscura employ Daguerre may •
be put in a box two feet 'keg, two feet
price
of
the
eet
olteh apparatus
and two
and a half feet high ; the
may be from 400 francs to 4.20 francs ' price of
each metallic sheet is about three or fourfranc
M. Daguerre has entrusted the manufacture and
selling of the apparatus to the house of Al
roux, Gi-
roux, in the Rue de Coq, St. Honore.
We need hardly say that the most enthusiastic Cheers
responded from the grave benches even of the Academy,
on the termination of M. Arago's description ; and the
President, M. Chevreul, complimented M. Daguerre in
the warmest terms.—Literary Gazette.

The wet and warm weather whieh we had for e
list few d lys in the n
ourhood of Dublin is consideredvery unfavourable. Nevertheless the accounts which we
have received from al! part 3 of the country are generally
satisfactory.—Dublin Evening Post.
E.—The Cas-
STORMS IN THE CASFIA SEA
.—The
Sea, which is generally so tranquil, was violently
agitated by storms in the early part of July. Eighteen
Russian and Persian vessels, valued with their cargoes at
three millions of rubles, were wrecked, and ninety-fives
lives were lost.
DON CARLoS TAKEN PRISONER.—It is ru-
moured
that the Devon lighter, which arrived here yester-
day, with despatches from the North Coast of Spa'n, has
brought hone the rims that Don Cbrlos is taken prsoner.
—Plymouth Journal of Thursday.