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FRANK LESLIE’S NEW YORK JOURNAL. 167
Practical Instructions in the Art of Photography,
: CHAPTER 11.
8. Licur—-the agent by which we are enabled to
depict nature or art with an accuracy that baffles
the most experienced artist—is derived from the
sun. True it is that there are other sources of
light; but photographers have nothing to do with
them—they must only confine their attention to solar
light, and the chemical changes it produces
9. You observe the glorious sun, which
“ Was given to ¢x.cken slumbering nature,
And lead the seasons’ slow vicissitudes
Over the fertile breast of mother earth ;”
how it pours forth its beams,
“* Dispensing life and light on every side;
Brightening the mountain cataract, dimly spied
, Through glittering mist, opening each dew-gemmed
lower,
Or touching, in some hamlet, far descried,
Its spiral wreaths of smoke that upward tower.”
And yet you know little of the nature of a sunbeam.
No doubt, you think that you do know what a sun-
beam is; but we question it—nay, are almost cer-
tain that you do not.. Ah! we were correct. Well,
then, to explain :—A solar beam of light is a bundle
of rays,* each of which possesses distinctive charac-
ters, both as regards their chemical functions and
colors, which you may very easily prove in some
respects at present, but more fully hereafter.
“10. We have found that a' sunbeam is a com-
pound—at least it has been stated that such is the
case; for Sir Isaac Newton proved that the white
light emitted from the sun is not so simple as it ap-
pears, but is composed of the most vivid colors and
tints that can be imagined. However, we will ex-
amine for ourselves, by performing the beautiful
experiment called ‘“ Newton’s Analysis of Light.”
{Experiment 1.] You observe that we have a prism
(6c, Fig. 1), or triangular mass of glass, which is
so contrived that it may be adjusted to any angle,
or placed in any position we may require. This is
not absolutely necessary, because the prism may be
held in the hand; but as we wish to have both our
hands free, we have arranged the apparatus as you
observe. We will now close the shutters of the
room, and admit a ray of light either by boring a
hole in the shutters or separating them a little.
[The ray of light (a e, Fig- 1), is admitted into the
: i - ‘darkened room bymeans
i roy of a hole (a) in the shat-
ter.] You see that the
space between the shut-
ter and ourselves is tra-
versed by the sunbeam
or ray of light, which
appears to cause little
particles of dust to
dance in the atmos-
phere of the. room.
This appearance, how-
ever, is due to the illt-
minating power of the
sunbeam contrasting with the other darkened: or
non-illuminated space in the room, as it renders the
small particles of dust floating in the air visible ;
but as the surrounding space 1s not*illuminated by
the solar light, we cannot distinguish the floating
particles of dust ; neither can we do so in the same
room when entirely lighted, because there is no sur-
rounding dark space to contrast with, or form a
background, as it were, to the sunbeam. “As soon
as the prism (dc, Fig. 1) is placed in the path of
the sunbeam, 80 as to allow it to fall on one of its
angles (b), the ray will be refracted, or bent out of
its course, so as to pass towards the back of the
prism (as in the line d), and not in the same line (a
e) that it would otherwise have done, had not the
prism been interposed. There is another effect, how-
ever takes place; for you observe that an elongated
delicately-colored image is formed upon
the wall (de); and if you stand at a
short distance from the prism you will
sce that these colors are spread out into
a triangular form, the base of which is
on the wall, and the apex, er point of
origin, at the back (c) of the prism. We
will remove the prism, and observe what
takes place. [Does so.] ow, you see
that the splendid display of colors upon
the wall has disappeared, and a round
spot of white light (e) is seen below the
place occupied by the solar spectrum.
11. The colored image you saw upon
the wall is called the prismatic or solar
Fig. 1.
* A ray of light ig the smallest portion of light which can
emanate from a luminous body; and although generally
represented by a mathematical line, it is really an infini-
tesimal pyrami
spectrum, which, according to Sir Isaac Newton, is
composed of seven different colors (see Fig. 2). The
color at the lower portion of the image, or that
nearest to the round white spot (e), which appeared
on the wall when the prism was removed, is of a
ted color, and the one at the other end is of a violet
color; the whole intermediate parts being occupied
by five other colors, and the whole arranged thus:
Orange.
Bettom,
The red ray is the least, and the violet the most re-
fracted of this chromatic image.* If the spectrum
e divided into 360 equal parts, corresponding with
the 360 degrees of a circle, the prismatic colors will
be found to occupy the following number of parts :
Since Newton’s time various experiments have
been instituted by many philosophers, who have
detected other rays; for instance, @ crimson or ez-
treme red ray has been
discovered below the red
ray, by examining the
solar spectrum through
a deep blue glass; and
Sir John Herschel ob-
served a lavender ray,
beyond the violet ray,
by throwing the spec-
trum upon a piece of
yellow paper. Mr.Stokes
has proved the existence
of an extra spectral ray
far beyond the violet;
but, as we have remarked before, our consideration
of light does not extend beyond its practical use to
photographers, and therefore we do not intend to
discuss the science of optics in the full sense, but
merely to become familiar with those facts that will
prove serviceable to us in our future researches.
12. Sir Isaac Newton was of opinion that white
light was composed of seven primary rays, each
possessed of a certain degree
of refrangibility, or capability
of being turned out of its
natural course; and he also
considered that the color of
a ray indicated its angle of
tefraction. Sir David Brews-
ter has demonstrated that
the seven primary colors, as
Sir Isaac Newton called the
tays of the solar spectrum,
are not primary, but that on-
ly three of them are so—viz.,
blue, yellow, and red; the
rest are compounds’ of the
three primary colors, which
form the spectrum by over-
lapping each other.
13. [Experiment 2.] If we
take a disc of cardboard (Fig.
3, and DD, Fig. 4), and di-
vide it into seven parts, each
of which is painted with one
of the-colors of the solar
spectrum, and affix it to an
axis (A, Fig. 4) which passes
through a stand, and is caused to revorve very rapidly
by pulling a string (S) wound around the axis; the
colors will blend, so that the impression made upon
impression made upon the retina by one color is not
stronger than that made by any of the others. It
Was thought that white light was the result; but
this was proved to be an error by pasting a small
strip of white paper across the indigo, blue, or any
Fig. 3.
Fig. 4.
* Fraunhofer measured the length of each of these rays
with great care, and has stated the following to be the
result of his investigations i
joiet, + - - 2 + + 109
Indigo, © + - - + - 47
ue - - + 48
Green, 46
Yellow, 27
Orange, - + 27
ed, - = 56
Totallength, - - 300 ~
other dark-colored segment, when it will be found
that the color caused by the revolution of the disc,
contrasted with the white paper, is anything but
white. Although somewhat out of place, we may
remark, that if the electric light be employed to il-
luminate the disc during its rapid revolutions, the
seven colors will be distinctly visible.
To be continued.
Tae Hone or rar Avruor or “ Wavertey.”—
The entrance-hall at Abbotsford is not very large,
but is beautiful, and tastefully hung with armor,
antlers, weapons, and interesting relics from many
lands. But after the guide pointed to a glass case,
which contained the suit of clothes last worn by Sir
Walter, I saw nothing beside in this apartment.
These brought the picture of the grand old man,
worn down and broken before his time, with won-
drous vividness before me. I could see him as he
totiered about his grounds, or sat in the shade of
some favorite tree, with his faithful Willie Laidlaw
—the great soul light in his eye dimmed with deep-
ening mists, and his gigantic genius shrunken into
a babe’s bounded and bewildered capacity. I could
see on his worn brow the troubled struggle of mem-
ory and thought, in his eyes the faint momentary
gleaming of the old inspiration; but by the sweet,
mournful smile of his wan lips, I could see—ah!
nothing more, for the real tears which rained from
my eyes seemed to hide the unreal picture of my
fancy. In the beautiful little study in which the
great novelist wrote many of his works, I felt the
air surcharged with the living magnetism of his
genius. So near he seemed, so strangely recent his
presence, so inevitable his speedy return, my mind
grew bewildered, and my heart beat hurriedly and
half expectantly. My very senses obeyed the strong
illusion of my excited imagination. I looked towards
the door by which he used to enter. I listened, and
spoke low. I dared not approach his writing-table
and sit in his chair, for fear he might surprise me
when he should come in. But, oh, how soon passed
over my heart the chill returning wave of recollec-
tion, of reason! Gone, gone fur ever—dust, dust,
these twenty years! The library, drawing and
dining-rooms, are very elegant apartments, com-
manding some charming views. There are several
fine pictures, by foreign artists, collected by Sir
Walter; but of more interest to me were the family
portraits. Of these there are two of the poct taken
in his early boyhood, wonderfully like those painted
in his manhood and old age. There is a handsome
full-length likeness of the last Sir Walter, and several
portraits of his sister, Mrs. Lockhart, whose son 18
present master of Abbotsford. .Of all the weapons
curious and memorable in the armory, of all the
valuable relics, I was most moved by the sight of
the pistols of Napoleon, Rob Roy’s gun, and the
sword of Montrose.— Grace Greenwood. .
Frencu Lirerary Women.—To this day Madame
de Sévigné remains the single instance of a woman
who is supreme in a class of literature which has
engaged the ambition of men ; Madame Dacier still
reigns. the queen of blue-stockings, though women
have long studied Greek without shame; Madame de
Stael’s name still rises first to the lips when we are
asked to mention a woman of great intellectual
power; Madame Roland is still the unrivalled type
of the sagacious and sternly heroic, yet loveable
woman; George Sand is the unapproached artist
who, to Jean Jacques’ eloquence and deep sense of
external nature, unites the clear delineation of cha-
racter and the tragic depth of passion. These great
names, which mark different epochs, soar like tall
pines amidst a forest of less conspicuous, but no less
fascinating, female writers ; and beneath these again
are spread, like a thicket of hawthorns, eglantines,
and honeysuckles, the women who are known rather
by what they stimulated men to write than by what
they wrote themselves—the women whose tact, wit,
and personal radiance created the atmosphere of the
salon where literature, philosophy, and science,
emancipated from the trammels of pedantry and
technicality, entered on a brighter stage of exist-
ence.
New Discovery at Assyria.—Mr. W. K. Loftus,
who is exploring Assyria and the ruins of Babyton,
writes from Mossoul ;—‘'! have discovered a palace
twenty feet below the level of any that has yet been
found, and have disinterred some specimens of the
most exquisite Assyrian sculpture. No comparison
can be made between the sculptures now discovered
and those previously found. The figures are in high
relief, and closely resemble nature. ‘The design is
full of force and life, the executiun wonderful, and
the finish of the details carried to, perfection.””
A sustice of the peace sometime may be beholden
to his friend for a man.
I
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