448 



POSITION OF PROJECTION APPARATUS [Cn. XII 



A Cross section showing the window shade (Sh) behind the thin boards 

 (W W) which serve to exclude the light at the top, sides and bottom of the 

 shade. 



B Face view of the window with the" light-excluding shade (Sh) shown in 

 dotted lines, (L) indicates the size of the window frame. The sash cuts this 

 down somewhat and the thin board frame to cut out the light around the edge 

 of the curtain cuts it down considerably more. 



C Lateral view of the window with the shade in dotted lines. The light- 

 excluding frame around the edge is in full lines in B and C. 



613. Position of the projection apparatus with a level room. 



In a level room, the projection apparatus at the back of the room 

 must be at such a level that the projection beam goes over the 

 heads of the spectators. This can be accomplished by building a 

 platform, or by using a high table. In case the image is still not 

 high enough on the screen, the lantern can be tilted slightly upward 

 by putting a wedge under the end of the baseboard supporting it 

 (fig. 240).. 



FIG. 240. SECTIONAL VIEW OF A LECTURE ROOM HAVING A GALLERY. 



B Black-board. This is lighted by incandescent lamps behind a curved, 

 metal shield (H L). This gives plenty of light for the black-board without in 

 any way injuring the brilliancy of the screen image. 



L T Lecturer's table on the platform (P). 



Ml The magic lantern in the gallery on its table and special support ( T). 



Sc Screenjfor the image above the black-board. 



