Appendix II 171 



liquids, to throw a continuous spectrum or a parallel beam upon 

 the screen, to project ordinary microscope slides, polariscope work, 

 galvanometer needles and scales, and is practically serviceable in 

 every way required by the chemical, physical, and histological 

 demonstrator. The lantern is illustrated herewith (Fig. 118); it 

 is supplied at reasonable price, with limelight, or arc lamp 

 fittings (or both), and is altogether satisfactory both from the point 

 of view of prime cost and of convenience in working. Special 

 tables and supporting rods are provided, while ample space for 

 apparatus exists between condenser and objective, rendering the 

 whole instrument compact, and specially suitable for general class- 

 room, as well as lecture, demonstrations. 



The actual projection of slides is attained by fixing the lantern 

 upon a canting table, lighting up, and first centring the radiant, 

 moving it horizontally and vertically until the screen is evenly 

 illuminated. The carrier is then placed in position, a slide 

 inserted, and the objective moved by the rough adjustments until 

 a fairly clear image is formed upon the screen. The fine rack and 

 pinion adjustment is then used to secure the best possible 

 definition. 



Lanterns without the fine adjustment for the objective should 

 not be used, as the focus varies according to the thickness of the 

 slide, and rough adjustments are not sufficiently steady to enable 

 small variations of this character to be dealt with easily. 



In the projection of apparatus, or cell work, little difficulty will 

 be experienced if it be remembered that the objects projected 

 should be as near as possible to the condenser. Slits for spectro- 

 scopic experiments may be cut from a sheet of copper, of such size 

 as to fit the carrier-supporting device, cells may be made to a 

 similar gauge, and apparatus suitable for projection always made 

 to fit these devices. In this way a most valuable collection of 

 projection apparatus will be gathered together, and the lantern 

 above recommended is the only one known to the author, which, 

 at a reasonable price, is capable of such development. Lanterns 

 with a single rod carrying the objective and erecting prism should 

 be avoided, as a single support does not permit of appliances of the 

 microscope, or spectroscopic prism type being placed easily in 

 position. Two supports are really necessary in order to secure 

 comfort in rapid and varied demonstrations. 



