Appendix I 165 



Kingsway, London, in shilling bottles. It is used exactly in the same 

 way as writing ink, with a steel pen it quickly sets hard, and is 

 then only removed by scraping. Any drawings or writing done on 

 glass with this ink may be converted into lantern slides by masking, 

 covering, and binding as before. The ink is of special value in 

 the drawing of sketches or diagrams upon a glass plate while in 

 the lantern, thus giving all the advantages of a blackboard and a 

 lantern slide combined. 



4. Slides made by Mounting Objects such as Crystals, 

 etc. Large objects are rarely suitable for lantern slides, leaves, 

 and similar objects being usually so thick as to produce a slide 

 wider than the ordinary lantern carrier will accommodate. 

 Crystals rarely form with sufficient distinctness upon a 3}" square 

 plate to be worth projecting, but many such objects lend themselves 

 to projection by the aid of a microscope. 



A microscope slide is usually 3" x i" in size, and if crystals be 

 prepared by spreading a drop of cold saturated solution upon them, 

 and slowly evaporating it, they may be preserved and used as 

 slides. 



A very suitable way of performing this is to use a small flat 

 ring or " cell " made of tin, and obtainable from dealers in micro- 

 scopic appliances ; moisten this on both sides with " Hollis' glue " 

 (shellac, spirit, and beeswax), place in position upon the plate, and 

 immediately cover with a circular " cover slip," specially made for 

 microscopic work. 



Many other objects may be similarly mounted. 



Projection is accomplished by fixing a 2" objective in a retort 

 stand clamp, placing it in front of the condenser of the lantern so 

 that the lens faces the condenser, at the point where the pencil of 

 light converges. The slide is placed between this objective and 

 the condenser, care being taken to hold it vertically. It will be 

 seen that an ordinary microscope without the eye-piece would form 

 an effective stage and holder for the slide and objective, and it 

 would also screen off unnecessary light. By this means an ordi- 

 nary microscope may be used for the projection of practically all 

 microscope slides, but no objective of higher power than i" is suit- 

 able for limelight lanterns ; J" or J" may be used with the arc 

 lamp, but considerable risk is run of damaging lens and slide by 

 the heat, unless a lantern cell containing a solution of alum be 

 interposed immediately in front of the condenser. This will 

 effectually stop all the heat. 



