Magic Lantern And Dissolving Views. The principle of construction is very simple. It consists of a tin box, with a bent funnel at the top, which serves for the double purpose of allowing the smoke and heat to escape, and preventing the light dispersing in the room, and thus interfering with the reflected image. It has a door at the side, a polished tin concave reflector at the back of the inside, and a powerful light placed in the focus of the reflector; the light being supplied by an argand, oil, or gas lamp, or by the combustion of oxygen and hydrogen gases thrown upon lime. For private exhibitions, the oil argand lamp is generally and more easily employed. Opposite to the light and focus of the reflector is a moveable or telescopic tube, containing a hemispherical illuminating lens near to the reflector, and a convex lens at the extremity of the tube; and between the two lenses is a slit for the introduction of the painted glass slides. The general form of the magic-lantern is shown in figure 7, which represents two lanterns (B and L) arranged for exhibiting the dissolving views.
To use the Magic-lantern. Light the lamp, polish the reflector with a dry cloth, and also carefully wipe the lenses to remove any moisture; then place the lamp in the focus of the reflector, close the door of the lantern, and place it upon a table ready for use. Suspend a wet sheet from a line stretched across the room, or have a screen made of calico stretched tightly upon a frame; in the event of not using either of them, you must reflect the images upon a smooth white-washed wall. Slip in a slide with the figures, and other subjects, inverted, or upside down, - then advance or recede with the lantern, and by moving the tube in front of the slide you will be enabled to adjust the focus, and obtain a magnified image of the painting upon the slide reflected upon the screen, sheet, or wall. When the room is large enough, it is better to place the screen between the spectators and the lantern, as it renders the deception more complete.
The Magic-lantern Slides may be formed of long strips of glass, cut of sufficient width to pass freely in and out of the slit in the tube of the lantern, and if the designs are not valuable, the edges of the slides may be simply bordered with paper to prevent them injuring the tube.
If, on the contrary, the paintings are good and worth preserving, the glass should be placed in a wooden frame, similar to that shown in the above figure, each slide being numbered or labelled; and the painted surface protected by another slip of glas3 placed over it, and fixed in the frame.
The most amusing objects for the slides are grotesque figures ; sudden transformations, such as a cabbage turning into a tailor, or a basket of eggs into a nest of birds; and moving figures and objects, such as a cobbler at work, a tight-rope dancer, a storm coming on at sea, in which the ship appears to be struck by lightning and consumed ; the eruption of Vesuvius ; or a railroad with the train passing along. The movements of the figures and objects are obtained by painting the subject upon two glasses, which are fixed in the same frame, and so arranged, that, when one is drawn aside or moved upwards or downwards, the first design is concealed, or else another one is added to it.
Sometimes several figures are contained in the same slide; and when the subjects are distinct, such as objects of natural history, or small interior views, etc. the slide is made of mahogany or deal, with circular pieces cut out in such a manner as to leave a rabbet on one side. The paintings, protected by a plain piece of glass, are then dropped into the holes, and confined by Small brads, or a thin piece of wood turned to tit in the hole, and each painting numbered or labelled, so as to prevent mistakes, and for the convenience of reference.
Dissolving Views. We have already seen, that, when a magic-lantern is used, a view painted upon the slide employed may be produced in a magnified form upon a screen, sheet, or wall. Now, if we employ two lanterns instead of one, it necessarily follows that we shall have two views distinctly thrown upon the screen. Practice will soon enable you to observe, that, by altering the focus of the lens after the clear image has been reflected upon the screen, the view becomes dim, and gradually dissolves if the focus is still further altered. If the lens of the second lantern, which is supplied with another view, is gradually brought up to the proper focus, the first view may then be said to have dissolved, and assumed the form of the second. The second view then dissolves, and a third takes its place, and so on - the chief object being to show a view which is made to fade gradually, and blend with a second view, which then becomes clear and bright, and fades, in its turn, to blend with a third.
The dissolving process may be effected in several ways : 1st. By altering the focus - a plan that succeeds for exhibitions on a small scale. 2nd. By placing the hand gradually over the nozzle of the lantern, and thus obscuring the view by degrees while a second slide is introduced, and, by gradually withdrawing the hand from before the nozzle, the second view is seen developing itself slowly and perfectly. These two plans are applicable for either single or double small lanterns. The best method of dissolving is undoubtedly that employed in all large apparatus, viz., by means of dissolvers or fans, which may be shaped like the one F in fig. 4, 1) in fig. 7, or else like the one (fig. 3) in the margin. The first kind will be explained when describing the apparatus required for the. oxyhydro-gen lanterns; the last are simply two pieces of cardboard or tin, mounted upon metal stems (A), which are fixed in a piece of wood at such a distance from each other, and with the part (A) turned to the outside, so that the one fan obscures the light of one lantern, while the light of the other is displayed. By pulling or pushing the wood in which the fans are fixed, before the nozzles of the lanterns, the views will be dissolved easily and gradually, in such a manner that one view will merge into another so slowly that the change will appear almost supernatural, producing an effect peculiarly beautiful and attractive.