1216 



Megadiascope. 





Projection by reflected light of wood-cuts, drawings and flat objects (Megascope). Projection by reflected light 



Fig. 26. with long focus Objective. Fig. 26a. 



13. Projection with the Cinematograph. 



As the cinematograph has come into general use for depicting events, and, more recently, for 

 demonstrating medical operations and scientific processes, no description of the apparatus is necessary. 

 A comparatively simple apparatus such as that shown in Fig. 25 will suffice for the purpose. The cine- 

 matograph is placed on the optical bench in front of the condenser, and by turning a handle the photo 

 strips are fed backwards in front of the objective and are at the same time intermittently illuminated. 

 Very clear images are obtained. 







b) Employing reflected Light. 



14. Projection of Wood -cuts, Drawings and flat Objects (Fig. 26). 



Fig. 26 shows the arrangement for this method of projection. The megascope is placed 

 upon the megadiascope after the wood cover with the curtains has been removed. The illuminating 

 mirror is let down by depressing the spring held by the lever. The erecting mirror is placed on the 

 mount of the objective if this is not already firmly connected to the base plate. The image is focussed 

 on the screen by raising and lowering the objective by means of the actuating mechanism of the 

 objective mount. At a distance of 4,5 m. from the screen extraordinarily bright and sharp images 

 2x3 m. in size are obtained, the size of the original image being 13x18 cm. The remarks on 

 page 1204 as to size of image at other distances apply in this case also. With the megascope illus- 

 trated in Fig. 26 a (the objective of which is a Zeiss Tessar of long focus, 500 mm.) just as large 

 an image can be obtained at a distance of 10 m. Printed writing appears correctly and not reversed. 

 By shifting the position of the arc lamp or the parabolic mirror as the case may be, a smaller diameter 

 can be more brilliantly illuminated. In no case are the images on the screen inferior to those given by 

 other apparatus either as regards brilliancy or sharpness. 



Butterflies, beetles, coins and other flat objects can be projected in a very beautiful manner. 

 Coloured view cards can also be enlarged very well. Good wood-cuts give the best images, glossy photo- 

 graphs and illustrations produced by autotypography not being so well adapted for reproduction. 



15. Production of a narrow Pencil of Light for the Lissajous Curves, the Oscillograph, etc. 



In order to demonstrate the Lissajous curves objectively iise is made of a narrow pencil of 

 light which is directed on to the mirror of the tuning forks. Such a pencil results when a diaphragm 



Cl. 4668, 4989. 



