ACCESSORY INSTRUMENTS 153 



Lastly, let it be repeated, never to forget the alum trough 

 in the ordinary slide-stage. Without this, ordinary balsam- 

 mounted slides will be melted, and living objects rapidly killed 

 by a heat nearly boiling. 



For micro-projections of a higher class, the reader is 

 referred to Chapter XIII. 



CHAPTER XII 



APPAEATUS FOB SCIENTIFIC DEMONSTBATION 



83. Demonstrating Lanterns. Any good ordinary lantern 

 can, by a little modification, be made effective in almost any 

 class of demonstration. It may have a good microscope 

 fitted to it, as described in the next chapter, interchangeable 

 with the ordinary front. With a slide-stage open at the top, 

 it will project chemical and other tank experiments. With 

 accessory apparatus such as is presently mentioned, it will 

 perform optical experiments. And by withdrawing the front, 

 and arranging small apparatus in the rays from the condenser, 

 it will project that apparatus. But for certain preponderating 

 kinds of work, certain forms of lantern are best adapted ; and 

 for constant work, especially in educational institutions, the 

 form of lantern should therefore be determined with reference 

 to the kind of work to be chiefly done. 



The modification and use of the lantern in a cheap and simple 

 way to project pieces of apparatus as well as slides, was first 

 systematised in the schools of Germany. Fig. 81 represents 

 such a German school lantern. 



The essential points are that the flange-nozzle is entirely 

 removed, only an open spring-holder stage being left in the 

 front of the condensers ; that the objective is mounted in a 

 separate support, which can slide along the double-rail stand 



