The Daguerreian Society


On this day (September 28) in the year 1839, the following news
item appeared in "The New-Yorker" (Vol. VIII, No. 2; page 19-20):
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                                       From the London Athenaeum.

                PRINCIPLE OF THE DAGUERREOTYPE.

   I write to you to report--though of necessity hastily--the 
proceedings of the Academie des Sciences of Monday last, when M. Arago, 
in the presence of a crowded audience, which had besieged the doors of 
the Institute three hours before the commencement of the sitting, 
divulged the secret of M. Daguerre's invention, which has now, as you 
are aware, become public property.  Three drawings having been 
exhibited, by way of specimens, M. Arago began be recapitulating the 
discoveries--or rather hints toward discoveries--of former chemists.  He 
afterward dwelt upon the progressive experiments of M. Niepce, since 
carried out by M. Daguerre.  As, however, your columns already contain 
notices of these, I will come at once to the publication of the secret 
of the perfect invention; and in order to give you this as fully and 
clearly as possible, I send you an abstract from the report published in 
yesterday's Journal des Debats.
   M. Arago stated that, according to M. Daguerre's process, copper 
plated with silver is washed with a solution of nitric acid, for the 
purpose of cleansing its surface, and especially to remove the minute 
traces of copper which the layer of silver may contain.  This washing 
must be done with the greatest care, attention, and regularity.  M. 
Daguerre has observed, that better results are obtained from copper 
plated with silver, than from pure silver; whence it may be surmised, 
that electricity may be concerned in the action.
   After this preliminary preparation, the metallic plate is exposed, in 
a well-closed box, to the action of the vapor of iodine, with certain 
precautions.  A small quantity of iodine is placed at the bottom of the 
box, with a thin gauze between it and the plate, as it were to sift the 
vapor, and diffuse it equally.  It is also necessary to surround the 
plate with a small metallic frame, to prevent the vapor of iodine from 
condensing in larger quantities round the margin than in the centre; the 
whole success of the operation depending on the perfect uniformity of 
the layer of ioduret of silver thus formed.  The exact time to withdraw 
the sheet of plated copper from the vapor, is indicated by the plate 
assuming a yellow color.  M. Dumas, who has endeavored to ascertain the 
thickness of this deposit, states that it cannot be more than the 
millionth part of a millimetre.  The plate thus prepared is preserved 
with great care from the faintest action of light.  It is, in fact, so 
sensitive, that exposure for a tenth part of a second is more than 
sufficient to make an impression on it.
   At the bottom of the dark chamber, which M. Daguerre has reduced to 
small dimensions, is a plate of ground glass, which advances or recedes 
until the image of the object to be represented is perfectly clear and 
distinct.  When this is gained, the prepared plate is substituted for 
the ground glass, and receives the impression of the object.  The effect 
is produced in a very short time.  When the metallic plate is withdrawn, 
the impression is hardly to be seen, the action of a second vapor being 
necessary to bring it out distinctly.  The vapor of mercury is employed 
for this purpose.  It is remarkable, that the metallic plate, to be 
properly acted upon by the mercurial vapor, must be placed at a certain 
angle.  To this end, it is enclosed in a third box, at the bottom of 
which is placed a small dish filled with mercury.  If the picture is to 
be viewed in a vertical position, as is usually the case with 
engravings, it must receive the vapor of mercury at an angle of about 
45o[degrees].  If, on the contrary, it is to be viewed at that angle, 
the plate must be arranged in the box in a horizontal position.  The 
volatilization of the mercury must be assisted by a temperature of 
60o[degrees] (of Reaumur.)
   After these three operations, for the completion of the process, the 
plate must be plunged into a solution of hypo-sulphite of soda.  This 
solution acts most strongly on the parts which have been uninfluenced by 
light; the reverse of the mercurial vapor, which attacks exclusively 
that portion which has been acted on by the rays of light.  From this it 
might perhaps be imagined, that the lights are formed by the 
amalgamation of the silver with mercury, and the shadows by the 
sulphuret of silver formed by the hypo-sulphite.  M. Arago, however, 
formally declared the positive inability of the combined wisdom of 
physical, chemical and optical science, to offer any theory of these 
delicate and complicated operations, which might be even tolerably 
rational and satisfactory.
   The picture now produced is washed in distilled water, to give it 
that stability which is necessary to its bearing exposure to light 
without undergoing any farther change.
   After this statement of the details of M. Daguerre's discovery, M. 
Arago proceeded to speculate upon the improvements of which this 
beautiful application of optics was capable.  He adverted to M. 
Daguerre's hopes of discovering some farther method of fixing not merely 
the images of things, but also of their colors; a hope based upon the 
fact that, in the experiments which have been made with the solar 
spectrum, blue color has been seen to result from blue rays, orange 
color from orange, and so on with the others.  Sir John Herschel is sure 
that the red ray alone is without action.  The question arose, too, 
whether it will be possible to take portraits by this method?  M. Arago 
was disposed to answer in the affirmative.  A serious difficulty, 
however, presented itself:  Entire absence of motion on the part of the 
object is essential to the success of the operation; and this is 
impossible to be obtained from any face exposed to the influence of so 
intense a light.  M. Daguerre, however, believes that the interposition 
of a blue glass would in no way interfere with the action of the light 
on the prepared plate, while it would protect the sitter sufficiently 
from the action of the light.  The head could be easily fixed by means 
of supporting apparatus.  Another more important desideratum is, the 
means of rendering the picture unalterable by friction.  The substance 
of the pictures executed by the Daguerreotype is, in fact, so little 
solid--is so slightly deposited on the surface of the metallic plate, 
that the least friction destroys it, like a drawing in chalk; at 
present, it is necessary to cover it with glass.
   From his numerous experiments on the action of light on different 
substances, M. Daguerre has drawn the conclusion that the sun is not 
equally powerful at all times of the day, even at those instants when 
his light is the same above the horizon.  Thus, more satisfactory 
results are obtained at six in the morning than at six in the afternoon.  
From this, too, it is evident that the Daguerreotype is an instrument of 
exquisite sensibility for measuring the different intensities of light--
a subject which has hitherto been one of the most difficult problems in 
Natural Philosophy.  It is easy enough to measure the difference in 
intensity between two light viewed simultaneously: but when it is 
desired to compare daylight with a light produced in the night--that of 
the sun with that of the moon, for example--the results obtained have 
had no precision.  The preparation of M. Daguerre is influenced even by 
the light of the moon, to which all the preparations hitherto tried were 
insensible, even when the rays were concentrated by a powerful lens.
  In physics, M. Arago indicated some of the more immediate applications 
of the Daguerreotype independently of those which he had already 
mentioned in Photometry.  He instanced some of the most complex 
phenomena exhibited by the solar spectrum.  We know, for example, that 
the different colored rays are separated by black transversal lines, 
indicating the absence of these rays at certain parts; and the question 
arises whether there are also similar interruptions in the continuity of 
the chemical rays?  M. Arago proposes, as a simple solution of this 
question, to expose one of M. Daguerre's prepared plates to the action 
of a spectrum--an experiment which would prove whether the action of 
these rays is continuous or interrupted by blank spaces.
   I shall only add, that M. Daguerre has entered into a contract with 
Giroux, the celebrated toyman, for the practical application of his 
discovery; and that it is said he has already in petto some new results 
of importance, which he sill submit to the Academie at an early 
opportunity.


(All original errors of spelling/grammar have been retained. -G.E.)
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Posted for your enjoyment.      Gary W. Ewer       
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09-28-95


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