452 



POSITION OF PROJECTION APPARATUS [Cn. XII 



screen, but as the distance is usually considerable, the screen image 

 will be good on a vertical screen. The position of the lantern 

 should never be so high that the screen image will be distorted. 



617. Apparatus in the middle of the auditorium with raised 

 seats. If the apparatus cannot be at the back of the room in an 

 amphitheater then a space or alcove must be made somewhere in 

 the middle by omitting a certain number of seats. The machine 

 is liable to be more or less distracting if in the middle of the room, 

 but sometimes this cannot be avoided on account of distance or the 

 form of the amphitheater (fig. 241). 



FIG. 244. PART OF A LECTURE ROOM WITH THE MAGIC LANTERN ON THE 



LECTURE TABLE DIRECTED TOWARD THE AUDIENCE AND A MIRROR TO 



REFLECT THE IMAGE ON THE SCREEN IN FRONT OF THE AUDIENCE. 



B Black-board with hidden light behind the curved metal shield (H L). 



Ml M Magic lantern pointing toward the audience. The mirror reflects 

 the image back to the screen in front of the audience. The mirror also serves 

 as a shield. 



Sc The image screen. By means of the pulley and cord it is inclined on its 

 hinges at the lower edge toward the mirror of the magic lantern. In this case 

 it is not inclined sufficiently to meet the axial ray at right angles, hence there 

 will be some distortion of the image and the upper edge will not be in sharp 

 focus when the lower edge is. 



T Lecturer's table. With such an arrangement the lecturer can demon- 

 strate with the lantern conveniently, and still have the screen in front of the 

 audience. If he uses lantern slides they must be put in the holder facing the 

 objective, not the light or there would be a mirror image on the screen (fig. 213). 



