This is a very curious optical effect, producing a distorted and grotesque figure from a regular one. The term is derived from two Greek words, signifying a distortion of figure, and by its means many optical puzzles may be produced geometrically.

Take any subject, such as the portrait of a head; divide it vertically and horizontally with parallel lines, of which the outer sides shall form the boundary, A, B, C, D, and the whole shall be equidistant. Then, on a separate piece of paper, or cardboard, prepare a drawing similar to Fig. 2 by the following means:--

1. Draw a horizontal line, _a b_, equal to A B, and divide it into as many equal parts as the latter is divided.

2. Let fall a perpendicular line, _e v_, from the middle of _a b_, and then draw _s v_ parallel to _a b_.

3. Both _e v_ and _s v_ may be any length at pleasure, but the longer the first is, and the shorter the other, so will the anamorphoses be more and more deformed. The proportions in our figures are sufficiently different.

4. After having drawn from the point _v_ right lines, _v 1_, _v 2_, _v 3_, _v 4_, to the divisions of _a b_, draw the line _s b_, and through each point where _s b_ intersects the divergent lines draw other horizontal lines parallel to _a b_. We now have a _trapezium_, _a b c d_ divided into as many cells as the square in Fig. 1.

[Ill.u.s.tration: _Fig. 1._]

[Ill.u.s.tration: _Fig. 2._]

The next step is to fill up all the cells of Fig. 2 with portions of the device, proportionate to their position in Fig. 1. For instance, in Fig.

1 the nose is in the second vertical division from the left, and in the third and fourth horizontal divisions from the top, and that portion of the face must accordingly be placed in a corresponding part of Fig. 2.

By these means we procure the anamorphosis seen in Fig. 2, which when viewed from a particular position, will lose all its distortion, and a.s.sume an appearance resembling that in Fig. 1. This position lies immediately over the point _v_, and at a height above it equal to the length of the line _s v_; and the means of determining it are as follows.

Place the drawing horizontally before a window; take a slip of card, and rest its lower edge on the line _s v_, the card being accurately vertical; pierce a small hole in the card vertically over the point _v_, and at a height from it equal to the length of the line _s v_, then with the eye placed immediately behind the card, look through the orifice at the anamorphosis, and it will be found that as soon as it has become accustomed to the novelty of the experiment, the anamorphosis will lose its distortion, and appear almost exactly like the symmetrical figure.

It would be very difficult, and would require geometrical reasoning of a lengthened kind, to show why this particular form of construction should lead to such results.

THE COSMORAMA.

[Ill.u.s.tration]

The principle upon which the cosmorama is formed is so simple, that any person may easily fit up one in a small summer house, &c. Nothing more is necessary than to fix in a hole a double convex lens of about three feet focus, A, and at rather less than this distance a picture, B, is to be hung. To absorb all the rays of light but those necessary for seeing the picture, a squared frame of wood blackened on the inside is placed between the lens and the picture. The picture may be hung in a large box having a light coming in upon it from above, or in a small closet illuminated in the same manner. Should it be wished to show it by candle-light, a lamp, _c_, may be placed on the top of the wooden frame, and if the light of this be converged by a lens to a moderate radius, it will be more effective.

DISTORTED LANDSCAPES.

[Ill.u.s.tration]

Landscapes or other matters may be drawn so as to produce curious optical illusions by the following method. Take a piece of smooth white pasteboard and sketch the design upon it. p.r.i.c.k the outlines in every part with a fine pin or needle, then place the p.r.i.c.ked drawing in a perpendicular position, and put a lighted candle behind it. Place before it another piece of pasteboard, and follow with a pencil the lines given by the light, and you have produced a distorted landscape. Now take away the candle and the p.r.i.c.ked drawing, and place your eye where the light was, and the drawing will a.s.sume the regular form. To get your eye in the proper position, it will be advisable to cut out a piece of card according to the accompanying pattern, and raising it on its base, B, look through the hole at A, when the object will appear in its proper proportions.

[Ill.u.s.tration]

[Ill.u.s.tration]

PHOTOGRAPHY.

"Come like shadows, but not so depart."--SHAKSPEARE.

a.s.sociated with the use of iodine and bromine is an art which every intelligent boy may practise, if he will attend to the following precise details kindly furnished by Mr. Richard Thomas, of 10, Pall Mall, who has devoted many years to the careful study of all the processes connected with it, and from whom all the best apparatus and purest chemicals required may be obtained.

HOW TO MAKE THE NEGATIVE ON GLa.s.s, USING COLLODION BROMO-IODIZED FOR IRON DEVELOPMENT.

1. The edges of the gla.s.s should be ground all round, also slightly on the surface of the edges. This prevents contraction of the film, enabling it to resist the action of a heavy stream of water. Mark one side in the corner with a diamond, and upon this side bestow the greatest care.

2. _To clean the gla.s.s, if new._--Make a mixture of spirits of wine and solution of ammonia, equal parts; render it as thick as cream with tripoli; with a piece of cotton-wool kept for this purpose rub a small quant.i.ty over that side marked as described, wash well under a tap of water, and wipe dry with a piece of old linen, washed without soap, and kept scrupulously clean for this purpose. Plates should not, however, be cleaned in the operating room with the above mixture; the vapour of ammonia might prove injurious to the chemicals.

3. Now polish with an old white silk handkerchief. If this latter precaution be not taken, small particles of linen will be left upon the plate: these are perhaps only seen when draining off the collodion; they form nuclei and eddies, checking the collodion in its course. Some of these minute fibres are washed off, and contaminate the next picture. To all lovers of clean pictures our advice therefore is, having well dried the plate with old linen, lay it, clean side upwards, upon a few sheets of common glazed demy paper (not blotting), and rub it hard with the silk until sensibly warm: this has the double advantage of dispersing fibres and moisture, for all gla.s.s plates are slightly in a hygrometric condition. Double the silk rubber up to form a pad, and with this the gla.s.s must be firmly dusted down just before pouring on the collodion, which will then run most evenly: if the coated plate is now viewed by transmitted light, not a speck or blemish will be seen upon it. When a plate cleaned as above described is breathed upon, the moisture does not evaporate slowly, but _flies off_. Do not be afraid of putting the gla.s.s into an electrical condition with the silk rubber: on this account objections have been raised to the use of silk: practically, however, I find it a most valuable auxiliary in this starting-point of the process, the perfect manipulation of which makes an important difference in the value of the finished picture. What can be more inartistic and annoying to an educated eye than spots, patches, stars, and sky rockets, the forms and shapes of which rival, in numberless variety, a display of fireworks? Let us not, therefore, be contented with pictures, however good in other respects, presenting these deformities--so many blots on the photographic escutcheon.

_To clean a gla.s.s after having used it, when not varnished._--Wash off the collodion film with water, then clean the marked side with plain tripoli and water, and dry as above.

_To coat the plate._--First remove all the particles of dried collodion from the mouth of the bottle. Now pour upon the centre of the cleaned gla.s.s as much collodion as it will hold. Do not perform this operation hurriedly, take time, and systematically incline the plate in such a manner that the collodion may run into each corner in succession; when perfectly covered, pour off gently the excess into the bottle at one of the corners nearest to you: with observation and practice dexterity is easily acquired. There are many ways of coating the plate; each person will adopt that which practice teaches him is best. The pneumatic plate-holder is a convenient little instrument to use for holding the plate whilst pouring on the collodion: it may be used for both small and large plates.

Keep the corner of the gla.s.s plate in contact with the neck of the bottle whilst pouring off the collodion; otherwise the film will be wavy in places.

4. As soon as the collodion ceases to run, plunge the prepared gla.s.s gently, without stopping, into the nitrate of silver bath, which is prepared as follows. Into a 20-oz. stoppered bottle put nitrate of silver, 1 ozs.; distilled water, 4 ozs.: dissolve. To this solution add iodide of pota.s.sium, 4 grs., dissolved in 1 drachm of distilled water.

Mix these two solutions: the precipitate (iodide of silver) thus formed is by shaking entirely dissolved. Add 16 ozs. of distilled water, when the excess of iodide of silver is again thrown down, but in such a finely divided state as to render the saturation of the bath with iodide of silver perfect. Now drop in sufficient of the oxide of silver to turn the turbid yellow solution a dirty brown colour; so long as this effect is produced the quant.i.ty of oxide of silver, however much in excess, is of no consequence; shake the bottle well for ten minutes or so at intervals; then add alcohol, 30 minims, and filter; to the filtered solution add dilute nitric acid of the strength stated, 5 minims. The bath is now ready for use, and should be quite neutral.

5. Allow the prepared gla.s.s to remain in this bath from five to ten minutes, according to the temperature. Move it up and down three or four times whilst in the bath, in order to get rid of the greasy appearance on the surface: drain it, but not too closely. When in the frame, place upon the back a piece of common blotting-paper, to absorb moisture, and the two lower silver wires should also be covered with slips of blotting-paper; after which the sooner it is placed in the camera the better.

6. The time of exposure can only be ascertained by practice--no rules can be laid down; and I am unacquainted with any royal road, but that of experience, leading to constant success in this most important point.

7. The plate having been taken from the camera, and placed upon a levelled stand, or held in the hand, develop immediately the latent image with the following solution:--

_Iron developing solution._--Protosulphate of iron, oz.; glacial acetic acid, oz.; spirits of wine, oz.; distilled water, 8 ozs.: mix. Pour on of this solution only enough to cover the plate easily, commencing at that edge of the negative which stood uppermost in the camera; move the solution to and fro until it has become intimately mixed with the silver on the plate; then pour off into the developing gla.s.s, and _at once_ return it on to the plate. When as much intensity has been obtained as possible with the iron developer, it should be thoroughly removed by washing with water. Any intensity may be obtained afterwards by using either of the following solutions:--

8. _Intensifying solution._--Pyrogallic acid, 6 grs.; glacial acetic acid, oz.; distilled water, 6 ozs.: mix. A few drops of a 30-gr.

solution of nitrate of silver, the quant.i.ty to be regulated according to the intensity required, to be added, at the moment of using, to as much of the pyrogallic solution as may be necessary.

_Intensifying solution_ (another form).--1. Pyrogallic acid, 8 grs.; citric acid, 20 grs.; distilled water, 2 ozs. 2. Nitrate of silver, 8 grs.; distilled water, 2 ozs. Mix small quant.i.ties of the solutions 1 and 2, in equal portions, the moment before using.

The pyrogallic solution, made with good acetic acid, may be kept for a month or more in a cool place. Nevertheless, if the conditions of light and situation are unfavourable, I should prefer this solution just made.

The iron solutions act best when freshly prepared.

It is supposed by some that a prolonged action of the iron developer produces fogginess. This may be the case when impure or improperly prepared collodion is used, but certainly not when the preparation is pure and of the proper quality.

When the image is sufficiently intense, wash freely with common filtered water; then pour on a saturated solution of hyposulphate of soda, which should immediately remove the iodide of silver: wash again well with water; allow as much as the plate will hold to soak in for at least a quarter of an hour, changing the water occasionally, to remove all traces of hyposulphate; lastly, wash the plate with a little distilled water, stand up to dry, and, if required, varnish either with spirit or amber varnish.

The following solution is also very commonly used for fixing the negative:--Cyanide of pota.s.sium, oz.; water, 12 ozs.

Attention to the following rules and cautions will a.s.sist the operator in the production of perfect pictures:--

1. Do not disturb the deposit which will occasionally be found at the bottom of the bottle containing the collodion.

2. Remove all particles of dried film from the neck of the bottle before pouring the collodion on the plate.

3. Never use damp cloths, leathers, or buffs, for giving the final polish to the plate. Negatives with an indistinct and muddy surface are frequently produced from this cause.

4. Let the film set properly before immersion in the nitrate of silver bath: its condition can be ascertained by gently touching the lower part of the coated plate with the end of the finger.