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WONDERS OF SCIENCE. photography, made use of Daguerreotype
and Talbotype pictures as the most effi
cient means of producing the illusion of We are indebted to Professor Wheat- solid representation in his stereoscope, no stone for the discovery of the stereoscope, practical photographers availed themwhich elucidates the phenomenon of bino- selves of the discovery, and it remained cular vision, and, although known in the concealed in scientific records, until the scientific world for nearly fifteen years, subject was again brought into notice at has only lately attracted the attention and the British Association at Birmingham, in excited the curiosity of the public, from 1849, by Sir David Brewster. Professor its now general application to photo- Wheatstone's first stereoscope was comgraphic productions. Although Professor posed of two small mirrors placed at an Wheatstone, soon after the discovery of angle of 90°, and each reflecting to one
eye one of the two binocular images. He lecture at the Society of Arts, showed that afterwards constructed a refracting tele- these two binocular images were not scope, composed of two prisms of about exactly similar—that each had a different 8° each, placed between the eye and one perspective projection. He placed one picture, and refracting the two images on against the other, and being able to slide
intermediate space, where they them in a grooved frame, there was only coalesced. Sir David Brewster recom- one plane of the perspective in each mended a stereoscope somewhat similar, picture which by the superposition could but, instead of two common prisms, sup- produce a single image; the objects on plied with two semi-lenses, acting at the planes more distant or nearer were dissame time as refracting prisms, and as tinctly seen double; when the objects on magnifying glasses, by which the pictures the foreground plane were coinciding, all could be considerably enlarged. This the objects behind were more and more instrument was so constructed that all separated, according to the distance; direct reflection was avoided, which is an when the objects of the middle plane were indispensable arrangement for the inspec- coinciding, all the other objects before or tion of Daguerreotype surfaces; and this behind were separated ; and when the contrivance, and the convenient shape of more distant objects were coinciding, all the instrument, has been partly the cause the others before were more and more of its great popularity and usefulness. separated as they were nearer and nearer. This instrument was called by Sir David | Therefore, in observing the two binocular Brewster the lenticular stereoscope. pictures in the stereoscope, the eyes are Photography alone can produce two obliged to alter their convergence in a images perfectly identical to the two certain degree for each distance, and it is images on the two retinæ ; and if we can to that exertion, and to the duplicity of place them so that the right perspective the images, and their degree of separais seen only by the right eye, and the left tion both ways, that the mind has the perspective only by the left eye, both in sensation of relief and distance of all the the line of direct vision, we have on objects represented in the stereoscopic each retina the same representation we pictures, and the process is exactly the had from looking at the natural objects. same when looking in the stereoscope on This is precisely the effect of the stereo- the two binocular pictures, or when lookscope; therefore, in the stereoscope we ing naturally at the real objects. If the have the same sensation of solidity and two perspective projections of the distance as we have with two eyes. When Daguerreotype images are taken at a we look at a solid object, such as a cube greater angle than they are with the eyes or a statue, it is obvious that the right eye for the same apparent size, the optical sees some parts of the solid which the left axes have to alter their convergence in a eye cannot see, and vice versa. In look- greater ratio in passing from one point ing with two eyes, the objects appear solid to another; the double images within and and separated from eacn other, because we beyond the point of vision are are unconsciously taught to judge that separated than in the natural vision; and what is seen by one eye, and not by the from these two exaggerated effects we other, must be on a receding part of the conclude or feel that the objects are more solid, and hence the idea of solidity in our separated than they are in nature, and mind. When we direct our vision from that the distance or relief is greater. By an object upon an object nearer or more magnifying more or less the stereoscopic distant, we are obliged to shift the two pictures, we, by the same reason, increase retinæ in order to cause their axis to less or more the stereoscopic effect. This correspond with the new angle of vision, is exemplified by looking with a double and to obtain a single vision. This is opera glass. If we look through the large done with wonderful rapidity, and we are lens near the eye, we considerably decrease unconscious of the exertion. This pheno- the size of objects; and as the angle of menon is beautifully illustrated by two vision remains the same as for natural photographic pictures on glass, intended vision, the eyes have to alter more their for the stereoscope.
M. Claudet, in a convergence, in surveying the various
planes, than they would have to do if the pictures placed in the stereoscope proobjects were really at the distance at duced less relief than one of these pictures which they appear to be. In looking seen alone with one eye. From this fact through the eye-pieces of the same opera- he proves why painting can never repreglass, we have a contrary effect, and a sent the distance and relief of nature, very unpleasant one, as we magnify the or stereoscopic vision; that the vision pictures. If they were seen by the eyes with two eyes of a monocular picture at the distance they appear to be, the gives a sensation of less relief and disangle of the optical axes would be larger | tance than with one eye. than the natural angle; and the exertion in converging from one point to another of the magnified picture is less through
THE WORK-TABLE FRIEND. the opera-glass than it should be if we were looking at the distance giving the
EMBROIDERED SCENT BAG. same size of image on the retina. For Materials.-A square of silk canvas, rather
more than twice the size represented in the enthis reason double opera - glasses are
graving; a skein of ombré green netting silk, defective, and produce an incongruous one of rose ditto; a little violet, blue, and sensation, which is very disagreeable. A yellow netting silk; 4 yard of white silk fringe, single opera-glass is far preferable, and
some white satin, pot-pourri, &c. gives an idea of greater distance between The design of the wreath of flowers the objects, and more relief of their embroidered on this scent-bag must be various parts, than a double glass. One enlarged to about twice the size repreof the most remarkable phenomena to sented in the engraving. Still further inwhich M. Claudet referred, the creased, and worked on kid or cloth, it is singular similarity of effect between suitable for the mats now so much used as squinting outwards and the stereoscope, stands for the ornaments on the manteland squinting inwards and the pseudo- piece. scope, when looking at two binocular All the foliage, various as it is, is worked pictures ; for by squinting either way, with the one skein of green silk, a needlewe can bring the right and left pictures ful of the darkest part being taken for on corresponding parts of the two retinæ. some of the leaves, the very lightest tints In squinting outwards on a stereoscopic being selected for others, and the medium slide we have, without the stereoscope, colours for the remainder. They must be the effect of relief and distance; and by worked according to the taste, and so as squinting inwards, the same effect of to produce the greatest possible varietyintaglio and inverted distances we have two leaves of a similar tint never coming with the pseudoscope, and by squinting together. The leaves are done in the vice versa we have a contrary effect. It usual way; the veinings up the centre in is easier to squint inwards, as we do when half-polka stitch. Besides all the foliage, looking near our nose ; and to obtain, by another part of the design is also worked so squinting, the stereoscopic effect in in green--that is, all the sprays of heath, examining the two pictures, we must the dots of which only are worked in place the right image under the left eye, scarlet, in French knots. The China and the left image under the right eye. asters are done in shades of violet, with In so doing we have the most beautiful yellow eyes, also worked in French knots. effect of relief and distance, and more The petals of those flowers are done by perfect than with the instrument, because using a double thread in the needle. The the prisms and lenses always cause a forget - me - nots are worked in French certain amount of distortion from spheri- knots ; five blue ones forms a small circle, cal and chromatic aberration. We have with a yellow one in the centre for the also another advantage, which is, that on eye. In working the roses, begin at the placing the pictures nearer or farther off, | heart of the flower, threading your needle we decrease or increase at will the stereo- so as to use the silk double. Take care scopic effect, or the relief and distances of that both the ends are of the same tint, the various parts of the picture. M. either the darkest or the lightest. Having Claudet showed that two exactly similar made a single French knot, with green
silk, in the eye of the flower, begin to work ! BRIOCHE CUSHION, BRAIDED ON
Materials.-Four pieces of coloured Frenca
this cushion is three-eighths of a yard, This embroidery requires to be worked which will cut into four pieces of the form in a frame.
given in the engraving. As the sections of To make it up, fill a muslin bag, of the the braid are usually all of different colours, proper size, with any pleasant scent, and four pieces, each containing the quantity cover it again with white silk or satin. named, will make four cushions; or if two Tack on the canvas on one side, sewing it colours only are used, two pieces will sufround the edges, and add the fringe.
fice for two. The materials will be forwarded for The design given in the engraving is 3s. 6d.; or the embroidered square of to be enlarged to the necessary size canvas, ready for making up, for the same for the cushion; pricked for pointing, charge; made up, 5s.
and then the same paper will do to mark For instructions in embroidery, see p. every section. After using the paper326, Vol. II, new series, Family Friend. pattern with prepared pounce, remove it,
and go over the whole design with a solu- | contrasts, and four different colours are tion of flake white and gum water. quite enough to look well.
The braiding is to be done in the usual A cushion marked with braid, sent for way, the stitches being always taken | 7s. 6d., post-free. across the thin part of the braid.
In selecting the merinos, violent contrasts should be avoided. The tints should A FASHIONABLE LADY OF THE FOURbe all either dark or light. Crimsons, TEENTH CENTURY.-Her head was engreens, dark blue, and claret, go well circled with a turban, or covered with a together; but if light pinks and blues species of mitre, of enormous height, from are among the shades, the joining colours the summit of which ribbons floated in the should be stone, drab, and a warm slate. air, like the streamers from the head of In arranging the braids, the same
Her tunic was half of one colour colours should be selected. Green, dark and half of another; a zone, deeply emblue, or violet looks well orange broidered and richly ornamented with merino, orange on green or blue, pink on gold, confined by her waist; and from it stone, or gray, dark blue on claret, were suspended in front two daggers, in crimson on green.
their respective pouches. Thus attired, If preferred, eight pieces may be cut she rode in the company of her knight to to form the round, instead of four ; but, jousts and tournaments.—Lingard's Hisin any case, there should be no strong ! tory of England.