THE FIRST SUN-PICTURES.
Humphry remained confined to his bed for many weeks, and every day his
mother dreaded seeing some development of the symptoms which generally
ensue from the bite of so rabid an animal; but the boy assured her, again
and again, that, owing to the promptitude of the remedies he had applied,
there was no cause for alarm.
While the youth was still a prisoner in his room, a gentleman came to
lodge at the house, and Humphry, to his great delight, learnt, in a
few days afterwards, that the new lodger was no less a person than Mr.
Gregory Watt, son of the celebrated James Watt, the inventor of the
present steam-engine.
It did not take long before the two became acquainted, and then Humphry
ascertained that the young Mr. Watt had but recently quitted the
University of Glasgow, and had been recommended by his physicians, owing
to his declining state of health, to reside for some time in the West of
England; hence the cause of his visit to Penzance.
Nor was Humphry long in discovering that the mind of his new friend
was enriched beyond his age with science and literature, and that
he possessed, like himself, a spirit devoted to the acquisition of
knowledge, and soaring far above the little vanities and distinctions
of the world. The two kindred spirits, therefore, soon contracted
an intimacy of the warmest nature; and this ultimately ripened into
a friendship which continued to the period of Mr. Watt’s premature
dissolution.
Mr. Gregory Watt felt not a little astonished, on being introduced to
the son of his landlady, to find him shortly afterwards speaking upon
subjects of metaphysics and poetry; for when Mr. Watt spoke to him of
the courage he had displayed at the time of the accident in excising the
wounded parts of his leg, Humphry confessed “that he had no belief in
the existence of pain, whenever the energies of the mind were directed
to counteract it.”[52] “For,” went on the boy, “in states of profound
attention, all perception of external things fades from the mind; the
clock in the room ticks, and we hear it not; persons enter the apartment,
and their presence is unheeded by us. And if by the intensity of the
intellectual operations the senses can cease performing their functions
in the one case, why not in the other? Martyrs at the stake have, while
in deep prayer, held their hand unmoved in the flames, and who can say
that the very fervour of their heavenly aspirations did not deprive them
of all sense of pain for the time being?”
Mr. Gregory Watt, however, had but little taste for metaphysical
discussions; and, smiling at Humphry’s stoicism, sought to divert the
conversation into a more congenial and practical channel.
The steam-engine that had been recently set up at the Wherry Mine by
Mr. Watt’s father became the theme of their converse; this soon led to
comments on the theory upon which its powers depended, and then Humphry’s
companion was surprised to find that a youth, who had been brought up in
an obscure town in Cornwall, was as well acquainted with the doctrine of
“latent heat”—and, indeed, the whole science of caloric—as he himself,
who had been reared, as it were, in a factory, where the workings of it
were every day visible.
The new laws of combustion naturally followed as the next subject
of discussion, when Humphry observed, “that he would undertake to
demolish the French theory in half-an-hour;” and so saying, he rapidly
ran over the experiments he had performed, to prove the falsity of
Lavoisier’s notions respecting the origin of heat during the burning of
substances.[53]
The lad had now touched the true chord, and the interest of Mr. Watt
becoming more excited, he conversed with young Davy upon his chemical
pursuits, and was at once astonished and delighted at his sagacity;
so that the couple—congenial in taste—already began to feel a growing
friendship for each other.
* * * * *
Humphry had quitted his chamber, but was still confined to the house,
from his inability to walk, when Mr. Watt—who had now known the youth
long enough to be proud of his acquaintance—returned from his morning’s
stroll along the sea-shore, in company with two friends whom he had met
in the town.
The gentlemen proved to be Mr. Josiah Wedgwood, the eminent potter of
Staffordshire, and his brother Thomas, who was alike distinguished for
his scientific abilities.
The learned potter was not long in Humphry’s company before he discovered
the high merits of the lad; nor was he a little pleased when he found
that the young Cornish apothecary knew all about the pyrometer he had
invented for measuring high degrees of heat by the contraction of
a ball of clay; and the old gentleman found considerable delight in
explaining to the boy the various processes concerned in the manufacture
of earthenware and porcelain, telling him anecdotes as to how Bernard
Palissy—who was the first to discover the means of giving a glaze to the
baked clay—had been reduced to such poverty by his experiments, that he
was forced to burn the doors, and even the boards, of the house in which
he lived, in order to get a supply of fuel for his furnaces; and how he
afterwards amassed an immense fortune by the invention, and ultimately
died in the French Bastille, a martyr to the Protestant creed, which he
had espoused. Mr. Wedgwood added that, “When we eat our food we little
think of the labour and privations that have been endured in order to
give a glassy surface to the plates and dishes upon which it is served;
for but few are aware that, previous to this invention, the ordinary
earthenware articles were more like tiles than our present crockery.”
Then Mr. Wedgwood talked with the youth about the rocks, inquiring
whether he had ever noticed any of the finer species of clay in those
parts, and was surprised to find how closely the boy had marked the
changes in the soil; for Humphry told him “he had observed that the
felspar in the granite decomposed long before either the mica or the
quartz, and that it was chiefly by the action of the atmosphere upon this
same felspar that the huge granite rocks became disintegrated, or broken
up; and that, as the felspar consisted principally of clay in the purest
form, he fancied that some advantage might be taken of this in producing
a finer species of porcelain than had yet been manufactured in this
country.”
The old gentleman thanked Humphry for his suggestion, and warmly praised
him for his observation and sagacity; whereupon the youth promised,
immediately that his leg would permit of his accompanying him, to point
out to Mr. Wedgwood the places where he had noticed the finest deposits
of felspar to occur.
The conversation then changed to a subject that Mr. Josiah Wedgwood said
“he had no doubt would be highly interesting to one of Humphry’s turn
of mind.” The old gentleman told the boy how his brother Thomas had
discovered a means of copying pictures upon glass, and even of fixing
the images of the _camera obscura_, by the action of light; “so that,”
he said, “the sun itself could be made to turn artist, and to produce a
representation of an object that no human hand could possibly rival.”
Humphry was enraptured with the new wonder, and more eager than ever to
learn all about it; so he begged Mr. Thomas Wedgwood to explain to him
the whole process.
“I should tell you, then,” said the potter’s brother, “that it has been
long known to chemists that a solution of _nitrate of silver_ (called
_lunar caustic_ in the shops), when washed over a sheet of paper—although
it does not undergo any change while kept in a dark place—will speedily
change colour on being exposed to daylight, and that then it passes
through different shades of grey and brown, and ultimately becomes nearly
black. These alterations in colour,” continued Mr. Thomas Wedgwood, “take
place more rapidly according as the light is more intense. In the direct
beams of the sun, two or three minutes are sufficient to cause it to
darken; whereas in the shade, several hours are required to produce the
full effect. The light, too, when transmitted through different-coloured
glasses, acts upon the nitrate of silver with different degrees of
intensity. It is found, for instance, that the sunbeams, when passed
through red or yellow glass (so that only red or yellow light shall fall
upon the paper), have very little action upon the lunar caustic; green
glass, however, is more efficacious, while blue and violet produce the
most decided and rapid changes.
“Now to make you clearly comprehend,” went on the gentleman, “the reason
of these changes, I should tell you that nitrate of silver consists
of nitric acid (aquafortis) and silver,[54] and that if a vessel of
pure and colourless nitric acid be exposed to the sun’s rays, it will
become decomposed, so that red fumes of nitrous acid will be evolved,
and these mixing partly with the liquid itself, will shortly turn it
to a reddish-brown tint. Well, the same change takes place when the
nitric acid is combined with the silver, and so made to form nitrate of
silver. The consequence is, that as the nitrous acid which is evolved is
unable to combine directly with the silver, the decomposed aquafortis is
dissipated in the form of vapour, while the silver itself remains behind
in the paper; and in such an extreme state of minute division, that the
particles, instead of being white, like ordinary silver, appear black to
our eyes.”
Humphry expressed himself delighted with the explanation, and said he
could now see how it was possible to produce sun-pictures by such means.
Still he begged Mr. Wedgwood to proceed.
That gentleman then told Humphry that his first attempt concerning the
production of sun-pictures, was to fix the evanescent images formed by
the camera obscura, but though he was able to impress these upon paper
in a bright sunlight, he found that he could not produce them in any
moderate time in ordinary daylight; so that, from the length of time
required before the impression was taken, the effects of light and shade
had materially altered. “With paintings on glass, however,” he added, “I
have been more successful; in order to copy these I apply the solution of
nitrate of silver to leather, for this I find to be more readily acted
upon than paper—probably owing to the tanning in the material. When the
surface of leather is thus prepared, I place it behind a painting upon
glass, and expose it to the solar light, when the rays, being transmitted
through the different parts of the picture, produce distinct gradations
of black and white, according to the lights and shades in the original;
for where the light passes freely through the glass, the colour of the
nitrate of silver, of course, becomes the deepest. By this means, then,
you will perceive that the lights and shades of my picture are entirely
reversed: all the black parts in the original being left white in the
copy, since the light, being unable to pass through these, cannot act
upon the solution; while all the white parts of the original, on the
other hand, become the blackest in the copy, owing to the rays passing
freely through the glass there, and so producing the strongest effect.
Accordingly, I am obliged to have the original pictures painted, in the
first instance, with their lights and shades reversed, or else I cover
another glass with a thin coating of isinglass, and apply the solution
of nitrate of silver to this; so that, when I have transferred the
original picture by this means to a second plate of glass, in which the
lights and shades are the direct opposite to what they are in nature, I
proceed to take a second copy of it—but this I do upon leather, as before
explained—and so obtain a perfect reproduction of the original, with all
the lights and shades in their proper places.
“But the same method of copying,” proceeded Mr. Wedgwood, “may be applied
to other purposes. It may be rendered subservient, for instance, for
making delineations of all such objects as are partly opaque and partly
transparent, such as leaves and the wings of insects. For this purpose
it is only necessary to put the objects to be copied between a plate of
glass and the prepared leather itself, when the sunlight, being more
or less intercepted by their forms, will leave the figures accurately
impressed upon the leather, so that they will appear as beautiful white
pictures upon a black ground. There is, however,” added Mr. Thomas
Wedgwood, “one great defect connected with the production of sun-pictures
by the means I have described, and this consists in the impossibility
of fixing them so that they shall be no longer susceptible of being
darkened when exposed to the light. I have already tried several methods
of obviating this difficulty. I have covered the sun-pictures with a
thin coating of varnish, but to no purpose, for they darken almost as
rapidly with the varnish over them as others do without it. Again, I have
submitted the pictures to frequent washings, in the hopes of dissolving
out of the paper or leather all the undecomposed nitrate of silver; yet,
even after this, a certain portion of the active matter still adheres to
the white parts of the sun-picture, and so causes them to blacken all
over on being exposed to the light. The consequence is, that the pictures
produced by the action of the sun must, in order to be preserved, be
examined always in the dark, and be kept continually in some place where
no light can penetrate.”
Humphry no sooner heard this than he suggested a number of expedients
by which he fancied the difficulty might be overcome; and as the lad
explained his reasons for the various methods he proposed, both Mr.
Wedgwood and his brother were as astonished at the extent of the boy’s
knowledge, as they were delighted with the acuteness of his sagacity.
The evening was passed in examining a portfolio of the sun-pictures that
Mr. Thomas Wedgwood had brought with him, and Humphry grew so charmed
with the then entirely novel process of “_photography_” that he declared
he would not rest until he had investigated the matter himself, and
ascertained experimentally whether any means could be found of rendering
the pictures permanent.