1208 



Megadiascope. 



Projection of horizontal Objects. 

 Fig. 6. 



Collection of Microscopical 

 Preparations. 

 Fig. 7b. 1:4. 



3. Projection of Apparatus independently of the Optical Bench of the Megadiascope. 



In addition to those apparatus which are set up on the bench of the megadiascope, there are 

 a number of such instruments, etc. which are placed independently in front of the condenser for the 

 purpose of being projected, as, for instance, Duboscq's polarisation apparatus, Mach's polarisation 

 apparatus, Paalzow's optical bench, the projection microscope for observing the existence of crystals, etc. 



To place these apparatus in position it is necessary to remove the optical bench: to this end 

 it can be pushed completely under the framework of the megadiascope, and is thus out of the way. 

 This arrangement has the further advantage that the bench when thus pushed away takes up no space 

 and is always ready at hand when required. 



We must not refrain from mentioning here that the foregoing methods of projection are of the 

 utmost importance for educational purposes, especially in connection with physics. In spite of this fact, 

 this projection is not possible at all in a number of new models of projectors, because attention has 

 not been given to what we have just mentioned, in designing such apparatus. Before purchasing a 

 projection apparatus, therefore, it is desirable to find out whether the model in view permits of the 

 projection of apparatus and the setting up of the optical bench in front of the projector. 



4. Projection of horizontal Objects. 



Horizontal objects are projected with the Horizontal Projection Apparatus (F i g. 6). This 

 consists of a wood baseplate with a frame completely surrounding it, underneath, and with a pillar 

 carrying an objective and erecting mirror fitted to it. Inside the frame a further mirror in metal mount 

 is arranged under the baseplate, and is capable of rotation, and it assumes an angle of 45 in conse- 

 quence of its own weight when the screw, with handle, shown to the left of F i g. 6 is screwed out. 

 Inversely, the mirror is raised and placed in a horizontal position when the screw is screwed in. In 

 the latter position the mirror fits into the frame surrounding the base. 



The baseplate carries a condenser of 150 mm. diameter and the pillar has a rack and pinion 

 arrangement for raising and lowering the projection objective. The tilting reversing prism is placed 

 on the mount of the objective and clamped with screws. The mirror is silvered on the front side, and 

 polished, and it must therefore not be touched with the fingers. 



3 



B 



Cl 4<iG4, 301. 



