On [page 247] I have told you how you can make a light and portable frame for the screen, at a small cost. Lads who have experimented in chemistry ought to be able to make the oxygen gas for the oxycalcium light.
Fig. 8.
This instrument, as here described, was intended for use only with the tin lanterns as sold in the shops, which all have tapering nozzles. It can, however, be used with the lantern described in my former article, but the stage of that lantern would require to be modified in the manner shown in [Fig. 8].
Unsolder the large nozzle-tube from the front of the stage, and in its place solder on a band-ring of stout tin. This band is to be one and a quarter inch deep, and the diameter just enough to allow of the back end of the nozzle-tube fitting in it very tightly when the lantern is used in the ordinary way. The small turned-out rim of the nozzle-tube must be carefully cut off for this purpose. The aphengescope itself must have a small tin tube fastened in the small hole in the front of it, for the focussing-tube of the lantern to slide in; and the large hole must be cut large enough for the tin band on the front of the stage of the lantern to fit into it. This arrangement will allow of the light in the lantern being brought closer to the picture than can be done with the ordinary lanterns, and will, of course, illuminate it more strongly.
A very good lamp, with high illuminating power, to be used in any lantern, especially with this instrument, can be bought at the paraffin-lamp shops for a small sum. The tin duplex lamp, burning crystal oil, is the best. I should recommend any of my readers who have made, or are about to make, the lantern I have described, to get one of these, instead of making the lamp described with it, as it will give nearly twice the light. An arrangement will of course have to be made at the back for the reflector. If a lamp cannot be got that is low enough for the lantern, you can make the body of it yourself. You can generally get, at these shops, damaged lamps at a small cost. Get one that is damaged only in the body. Unscrew the brass-work, as though you were about to fill it, and put it on one side. Unsolder the brass screw-socket from the reservoir. Now make a square tin box for the new reservoir, covering in the top. The box is to be an inch and a quarter deep, and as large as the lantern will allow. In the top cut a hole to solder the brass screw-socket into. Then screw in the brass wick-carrier and make the clip for the reflector.
If a pair of lanterns are used the light will be proportionately stronger, and a strong light is an important thing with this instrument.
Fig. 9.
[Fig. 9] gives the plan of the top and bottom boards of the instrument for use with a pair of lanterns, and requires no further description.