Negatives may be obtained by the aid of light given by burning magnesium wire, care being taken that the direct light does not fall on the lens, and that the object is well illuminated. Transparent positives on glass may be printed by the light of a gas-burner, or of an argand oil lamp.

The annexed figures show a cheap and simple magnesium lamp for printing lantern transparencies by contact. It consists of three parts: - Base, shade, and clip (to hold the magnesium.)

Fig. 62 shows section of base with dimensions in inches marked. It is made of wood, and turned circular in the lathe.

Fig. 62.

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Fig. 63.

Fig. 63 shows the shape of the shade before it is fastened on base. It is cut out of tin plate, has a cut at top for inserting clip; it is to be bent and will go about half round base, to which it must be fixed by screws.

Fig. 6+ shows clip in two parts; one is made of brass wire beat in the form shown, and the other is made of a piece of sheet brass about 1/16 in. wide.

Fig.65.

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Fig. 64.

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Fig. 65 shows the lamp complete, with the handle soldered on. The position of the clip inside the shade is shown by dotted lines. If the back of the shade be painted black, and a small saucer or tin tray be placed on the base to catch the ashes, it will be everything that can be desired. (A. P. Wire.)

The use of "Photo-powders" - that is explosive light-producing mixtures, the basis of which is magnesium - has more than doubled the Held of activity of instantaneous photography. But there is very great inconvenience, even danger, on account of the explosiveness of the substances which enter into the composition of these powders; then,too, there is the irritating action (on the lungs) of the clouds of smoke produced by combustion in the confined atmosphere of a room. The direct combustion of magnesium powder projected into a flame does away with these incon.

The apparatus described below is ex-tremely simple,small,and portable,easy to construct and to use, a vast improvement on the cumbrous and cosily arrangements which have hitherto been slightly widened, a small quantity of the powder is introduced. 2 grm. (a quantity which can roughly be judged by will produce a light amply sufficient nt. a distance of 3 yards for an object-glass of } in. aperature and 3 in. focal 1ength At the opposite end of the tube is a small rubber bulb, such as is used for ejecting a liquid from a bottle in the form of spray.

A small tube about 3 in. long and 1/8 in. in calibre, twisted like a huntsman's horn, constitutes the whole apparatus (vide Figs. 66 and 67). At One of the ends.

Fig. 66.

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Fig. 67.

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The ring of the tube is simply passed over the index finder, as in Fig, 66, or over the thumb, as in Fig. 68, the hand holding a lighted candle. Thus, the open end of the tube is presented obliquely to the largest part of the flame. All that is necessary now is to squeeze with the free hand the rubber ball, when the powder is projected into the candle-flame. A flash is produced instantaneously, which gives a light, rich in actinic power, sufficiently strong for the purpose of photography.

Other forms of attaching the tube to the candle can readily be devised - e. g. Fig. 67 shows the use of a coiled wire, thus leaving the hand free; or the tube itself may be coiled round the candle, or held with a clip, or by any other convenient means which the operator may devise.

The greatest advantage of this arrangement is, perhaps, the certainty and ease with which an operator can illuminate the field at the precise instant he may desire.

Fie. 68.

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Again, several of these candles may be arranged in position, the tubes connected with one rubber ball, which places them all under the control of the operator, who can thus produce a number of simultaneous flashes. (See also iv. 398.)