CH. IX ] PROJECTION MICROSCOPE 267 



This apparatus is designed to project opaque objects as large as 22 centimeters 

 in diameter, at a magnification 0/5 to 10 with a jo ampere current. For a smaller 

 object one may magnify as high as 25 diameters. With a 50 ampere current and a 

 larger reflector the magnification may be from 14 up to jj diameters. 



PROJECTION OF OPAQUE OBJECTS 



\ 428. Episcope.— For the projection of opaque objects like anatomical prep- 

 arations, figures in books, coins or indeed any opaque object an apparatus on the 

 principle of the one figured (Fig. 214) is used. That is, a powerful light is thrown 

 upon the opaque object and the rays reflected from the object are then projected 

 upon the screen by an objective as for a lantern slide. As the objects are mostly 

 in a horizontal position the objective points directly upward, and the rays from it 

 must be made horizontal by means of a 45 degree mirror or prism. 



This apparatus is very old. Its first name was "aphengescope" or opaque lan- 

 tern. Now it is called an episcope, or megascope, and if for both opaque and 

 transparent objects (Fig. 214) it is designated as an epidiascope. 



For its satisfactory use exceedingly powerful light must be used. Some opti- 

 cians employ two radiants, others but one. In any case currents of 30 to 50 am- 

 peres are used. One should wear deeply stained glasses in working with it. 



The apparatus works well with flat objects, and rather brilliant objects, like 

 the movements of a watch, etc. It is also more satisfactory for objects of slight 

 thickness. For objects like bones, etc., one must focus up and down for the dif- 

 ferent levels. 



REFERENCES TO CHAPTER IX 



Lewis Wright, Optical Projection ; Carpenter-Dallinger ; L,eiss, Die optischen 

 Instrumente der Firma R. Fuess ; The works on Photo-Micrography ; The latest 

 catalogs or special catalogs on projection apparatus issued by the opticians, especial- 

 ally Zeiss, Reichert and Leitz. The volumes of the microscopical periodicals for 

 the last few years, especially the Journal of the Royal Microscopical Society, and 

 the Zeitschrift fiir wissentschaftliche Mikroskopie. 



