through it, ought to be made as black as possible; for which purpose black velvet is very effectual. The rest of the inside, including the inner surface of the shades, ought to be white, in order to reflect light. The front of the box ought to be black outside, and surrounded by a black curtain.

It is necessary to have a small opening and tube through which an exhibitor may view the pictures, when the spectator is unacquainted with the management of the apparatus. It should be on the same level as the spectator's tube. If the box be large, so as to admit of a distance of 8 or 9 inches from the spectator's tube, it may be on the front; if not, it will be necessary to have it on the side close by the front, and the pictures may be reflected to it by a very small mirror within the box. There should be placed over and behind it, to screen the eye of the exhibitor from the light without, a black moveable shade, which may be conveniently made of two parts, the upright part to support the horizontal part when in use, and both when not in use to fold upon the box. The part of the box within this shade is to be painted black. The front and back shades should be fitted up in such a manner as to be opened conveniently, either by a spectator or by an exhibitor.

The box may be made of any size or proportions-the larger, the more striking the effect. And it may be supported upon a stand, or in any other manner convenient.

The annexed figures show a perspective view, side elevation, and plan of the box. The letters of reference are the same in all the figures.

A, Eye-hole for the spectator.

B,

Ditto for the exhibitor, with a shade over it.

C, Small mirror reflecting the picture to the exhibitor.

DEF, Form of front light.

HI, Triangle to prevent a too sudden increase of light on raising the shade RS.

KL, Picture in its groove.

MQN, Back-light. The slope NQ is close. The slope MQ is open. It

and the front-light DEF, are covered with tissue paper or other appropriate material. The back-shade PO extends beyond the opening. The intention of this construction is to admit the light in a proper position, and very gradually.

TT, Curtain hung in front, to shade completely the light from the spectator. XXX, Levers for raising the shades easily, with cords attached.

2. The Pictures.-The pictures may be either in watercolours upon paper, stretched in the usual manner on the frames, or in oil upon linen.

In painting the front, whether in water-colours or in oil, the lights are left out, as in ordinary water-colour painting, so as to admit the light from behind to pass through, and body colours are to be avoided. The back of the pictures is covered with a strong semi-transparent tint in those parts where it is wished that light shall not pass freely, or it may be rendered opaque if required. When painting the back, no light is to be used except that transmitted through the front.

Objects painted behind are, of course, not seen by the front light; and objects painted in front appear so faint when seen by transmitted light, that it is easy to paint the back in such a manner as to make them disappear when the back light only is admitted, by which means great changes may be produced.

For farther information with regard to the execution of the pictures, see Daguerre's description of his method of dioramic painting. There is an English translation of it by Dr Memes.

The appearance of fog, which is not mentioned in Daguerre's description, is produced by painting the objects intended to be affected by it on a second surface, immediately behind the front surface. Light is admitted behind. When the second surface is removed more or less from the other, the objects on it appear more or less involved in fog. And, as it is brought into contact with the other, the fog appears to clear away.

A great variety of effects of day-light and moon-light may be produced by judicious management of the pictures, and by the adoption of contrivances sufficiently known or obvious to those who have paid any attention to art generally.

3. The Light. In day-light the back of the box is placed close to a window, and no more light ought to be admitted into the apartment than is necessary fully to light the box. At night the openings may be lighted with oil or gas, or even with a few candles, if the box be small. The very strong orange tinge of ordinary artificial light is unfavourable to the

natural and pleasing effect of the pictures; but it may be so far counteracted where necessary, as sometimes in night-scenes or snow views, by interposing tissue-paper or other appropriate material, tinted blue.

The effect produced depends in a great measure on the management of the light, and a few experiments will soon enable any one to regulate its admission so as to exhibit every change of effect.

I have been induced, by the representations of friends, to bring this Portable Diorama under the notice of the Royal Scottish Society of Arts; and I have no doubt that the experiments of others may lead to many improvements in its construction. G. TAIT.

EDINBURGH, 1st November 1841.

Analyses of new Mineral Species. Communicated by Dr THOMAS ANDERSON of Leith.*

Aphrodite.-A mineral found at Taberg and Sala, and long supposed to be Meerschaum, has, on analysis, been found to be Serpentine. A mineral, however, of the same sort, from Langbanshyttan, and which is identical in external characters, is found to have a different composition, and has been called Aphrodite, whose composition is

This is therefore the third bi-silicate of magnesia which occurs; the other two being Picrosmine and Picrophylle.

Berzelite.-Under this name Kuhn has described a minéral from Langbanshyttan, of an impure dirty white or honey-yel

*The above communication was sent from Stockholm by Dr T. Anderson, who is at present studying there under Berzelius.

low colour, and of a waxy lustre. Sp. gr. 2.52; hard. 5-6. It gives signs of a cleavage plane; is brittle and easily pulverised; before the blowpipe behaves as Pharmacolite. It appears to be a mixture of arseniates of lime, magnesia, and manganese. The composition is

Esmarkite.-Under this name Erdmann has described a mineral found about 100 paces from the locality of the Praseolithe (to be afterwards noticed); it occurs in granite, in the form of large irregular crystals, which seem to be prismatic, with the edges and angles rounded; they are for the most part covered with a glittering coat. The crystals have an evident cleavage at right angles to the principal axis, and this cleavage has a feeble pearly lustre. The longitudinal fracture has a resinous lustre; hardness between calc spar and fluor spar; sp. gr. 2.709. Before the blowpipe gives water and becomes bluish grey; melts on the thin edges only, to a green glass; fuses with borax and microcosmic salt, with the colour of iron; gives a yellow slag with soda. Its composition is

Lime, oxides of copper, lead, cobalt, and titanium,

45.97

32.08

10.32

3.83

0.41

5.49

0.45

98.55

Euxenite.-Under this name Scheerer has described a mineral from Jölster in Norway. It is amorphous, dark brown, of a metallic resinous lustre, and has an imperfect conchoidal fracture. In thin plates it is transparent, with a red colour; gives a pale red powder; sp. gr. 4.60; hardness near that of Thorite, which, however, it scratches; does not melt alone before the blowpipe; fuses in borax and gives a yellow colour; with