40 THE ESSEX FIELD CLUB.
to show what enormous strides in the study of nature had been made directly a
new weapon had been placed in the hands of scientific workers. The object of
the present lecture was to show how the photographic plate had within the
knowledge of the present generation become an indispensable adjunct to science.
The lecturer said that the first successful photographs on silver salts were taken
by Daguerre2 who began his researches independently, but afterwards entered
into partnership with Joseph Nicephore Niepce, of Chalons ; the latter had
previously been taking photographs on metal plates coated with bitumen, a
method which endures to this day in photo-mechanical work. Fox-Talbot had
also been working independently in England with silver salts upon paper, and
his process was made public in this country about the same time that Daguerre's
method was made known in France, both of which events occurred in 1839.
After the publication of the discoveries of Daguerre and Fox-Talbot, the
chemical and optical departments of photography became united. The camera
obscura is said to have been invented by Porta in the sixteenth or seventeenth
century, but perhaps it was known to Roger Bacon in the thirteenth century.
As he intended to speak upon the scientific uses of photography, he would
first point out that the camera image, being formed by a lens, is not much limited
in size, either in the way of enlargement or reduction. For instance, a lady had
just placed in his hands the smallest Johnson's Dictionary in the world ; the
reading of it had to be done through a magnifying glass. As the little volume
was indirectly issued as an advertisement, he would not push it any further.
This reduction by means of photography was largely utilised during the siege of
Paris by the establishment of the pigeon post ; documents and newspapers were
photographed on a greatly reduced scale upon collodion films, which were then
stripped off the glass, placed in quills, and carried attached to the tail feathers
of the birds. When the destination was reached, these missives were pro-
jected on to a screen and enlarged, by means of the optical lantern, and anything
required from them was taken down by shorthand reporters in the room.
Mr. Meldola said that photography might be used for purposes of fraud, such,
for instance, as the representation of ghosts in the so-called "spirit photographs,"
and he exhibited some pictures on the screen, photographed by one of his students,
in which the person acting as ghost had been in position during but a portion
2 In a report of the lecture published in "Photography," I am credited with the statement that
Daguerre was the first to introduce silver salts into photography, and this statement is made the
subject of an editorial criticism. The writer of the note has. however, fallen into some error or
mutt have misunderstood my remark. That I was aware that Schnlze had previously experi-
mented with silver compounds appears from the following extract from my book on "The
Chemistry of Photography," which was published in 1889, the lectures forming the subject of
the work having been delivered in 1888:—" The first distinct statement as to the darkening of a
silver compound being the result of the influence of light was made by a German physician, J. H.
Schulze, who in 1727 observed that when a solution of silver in nitric acid was poured on to chalk
the precipitate darkened on the side exposed to light," etc, (p. 36).
Again, in a Friday evening discourse delivered at the Royal Institution on May 16th, 1890, I
said:—" If the word 'photography' be interpreted literally as writing or inscribing by light,
without any reference to the subsequent permanence of the inscription, then the person who
first intentionally caused a design to be imprinted by light upon a photo-sensitive compound must
be regarded as the first photographer. According to Dr Eder, of Vienna, we must place this
experiment to the credit of Johann Heinrich Schulze, the son of a German tailor, who was born
in the Duchy of Magdeburg, in Prussia, in 1687, and who died in 1744, after a life of extra-
ordinary activity as a linguist, theologian, physician, and philosopher. In the year 1727, when
experimenting on the subject of phosphorescence, Schulze observed that by pouring nitric acid, in
which some silver had previously been dissolved, on to chalk, the undissolved earthy residue had
acquired the property of darkening on exposure to light. This effect was shown to be due to
ligni, and not to heat. By pasting words cut out in paper on the side of the bottle containing
the precipitate, Schulze obtained copies of the letters on the silvered chalk. The German
philosopher certainly produced what might be called a temporary photogram." Proc. Roy. Inst.,
vol. xiii., p. 134 I have nothing to add to these extracts ; they are amply sufficient to show that
I was acquainted with the work of Schulze—R.M.