The lantern slide carrier may sound to some a very unimportant part of the lantern outfit, yet it is the very back-bone of a successful entertainment. Chad wick, who has done much to simplify lantern manipulations, has overcome, to a certain extent, the difficulty of exhibiting slides of various sizes. A universal size of slide would do much to advance the interests of photography and remove a load of anxiety from the mind of the lantern conductor. We would then be in a better position to exchange slides with other nations, and be sure of exhibiting them without any special arrangement In the form of our carriers.
Chadwiek's improved carrier is simple and effective enough when two lanterns are used, but for the mere purpose of exhibiting a seriesof photographic views there is no need of two lanterns, unlets it be for the purpose of effect, and that tainment. To see a picture come on the screen in its proper place and remain there quietly till the lecturer has passed his remarks upon it, and to pass as quietly away, is a pleasure we seldom enjoy under present circumstances. When a single lantern is used we are accustomed to see the pictures pass along the screen in regular, and ugly streak of black between each, caused by the binding of the two glasses and the round or cushion-shaped mask between them. Why this has been so long the form of mounting slides is difficult to understand: it is much better to leave ont the mask, and with the picture close up to the edge, bind only the top and bottom of the slide; and if the push-along process of exhibiting be adopted, we have something more approaching a panoramic effect, and the eye will not be so painfully impressed with what In reality appears more prominent than the picture itself, namely, its mask and binding.
This, with the single lantern, will be found a practical way of getting over the difficulty when slides of various sizes are to be exhibited; indeed there need be no limit to the length of the landscape slide, though for portraits the mask is indispensable. A universal size of slide, after all, would be the most acceptable.
Carrier for slides.
I shall now describe my carrier and the mode of using it. The only difficulty in the way of its being immediately adopted is that a special arrangement is necessary to be made with that part of the lantern which bears the lens. The improved Sciopticon requires no alteration except in the hood which shades the light between the condenser and the objective. The carrier requires no great amount of mechanical skill to effect the desired alteration. Figs. 58, 59 give some idea of the shape and mechanical, arrangements of the carrier in its improved form: -
A B Fig. 58 is the frame, which may be made of either wood or metal. C is a spindle which passes from side to side of the frame, terminating at each end with a suitable thumbscrew, by which it is turned in the act of changing the slide. D, two metal plates passed through the above spindle, which act as levers in pushing away the slide. £ may be called a self-acting balance lever, the form and action of which will be better seen in Fig. 59. F is a spring to counteract the force of the falling slide, upon which the successful working of the carrier much depends, in adjusting which be careful to give it a slight turn inwards, so that the slide on falling may not be forced outwards. Fig. 59 is a full size section of the principal part of the carrier as seen from the side: g is the spindle; h the self-acting balance lever, which is simply a plate of metal bent round the spindle in the form represented, the round black part of which is filled with lead, thus causing the lever to press against the slide «', and hold it in position till forced away by the spindle levers in the act of changing the slide.
In using the carrier, drop a slide in at the top of the frame at A B, Fig. 58, till it rests on the spring F. That being exhibited on the screen, drop another slide in at the top as before, while the spindle levers are lying in a horizontal position, thus preventing the top slide from coming in contact with the bottom one. The lecturer having finished his description of the view on the screen, gives the signal, while you give the thumb-screw C a slight turn, and, in a flash, the scene is changed. The slide, on being expelled from the carrier, falls forward upon a cushion or pad, from which it is removed during the description of the succeeding slide, and so on till the close of the lecture. (J. McKean.)
A difficulty with many has been that they cannot obtain coal gas; and they find the oxy-calcium process with spirits of wine not easy to manage. The symmetrical condenser is now much in use. A hint for steadying the jet and lime holder is by filing away the supporting rod on the side opposite to the screw. This simple plan is so effectual for the object designed that it ought to be generally known and adopted.
Sources of light are the first point for consideration. The forms are as follows: The lowest form of lime-light is the oxy-calcium or spirit-lamp jet. In this form a jet of oxygen gas is thrown on to a spirit-lamp flame, and, striking on a cylinder of lime, produces the lowest form of lime-light. This light, under usual conditions, is equal to 150 candles.
The next is the safety oxy-hydrogen jet. Here we use a jet of gas from the nearest gas fitting, and through this the oxygen jet is thrown, as described, on to the lime. This form is perfectly safe, and gives a light equal to 190-200 candles.