28 MAGIC LANTERN WITH DIRECT CURRENT [Cn. I 



3. In the slide-changer of the Spencer Lens Co.'s magic lan- 

 terns (Delineascopes) , the slide is laid flat, with the face 

 up, i. e., so it will be toward the condenser when ready for 

 projection. The edge which is to be uppermost in the 

 ordinary vertical carrier, is toward the screen. Now when 

 this slide-changer is used it turns the slide up in the ver- 

 tical position so that it is in precisely the same position as 

 with the ordinary slide carrier. 



36. Possible ways of inserting American lantern slides in the 

 slide - carrier. The standard American lantern slide is oblong 

 (10x8.2 cm.; 4x3^ in.), and the carriers are constructed to 

 receive them lengthwise. While they would never be inserted 

 with the short edge up, they can be inserted with either long edge 

 up, and facing in either direction. This gives four possible posi- 

 tions in the carrier, only one of which is correct. That is, there are 

 three wrong ways of inserting the slide in the carrier with the 

 corresponding wrong images on the screen. It is not very uncom- 

 mon for an audience to see all possible images of the same slide, and 

 occasionally the wrong ones repeated once or twice. This is as 

 inexcusable as it is unnecessary (fig. 10-12). 



37. Possible ways of inserting the square English lantern 

 slides. These slides are 8.3 x 8.3 cm. (3^x3^ in.), and being 

 square they may be put into the carrier with any of the four edges 

 up, and of course with either face toward the lamp. This gives 

 eight possible ways of insertion, seven of which are wrong. Square 

 slides must have two "spots," (see fig. 13). 



38. Focusing the image on the screen. When the lantern 

 slide is in the correct position before the condenser (fig. 1-2) the 

 objective must be at such a distance from the slide that the screen 

 image will be sharp, and show clearly the printed matter and all 

 the details of the picture. With the usual magic lantern the 

 objective is nearly in the right position all of the time. But for 

 any necessary final focusing there is a rack and pinion on the 

 objective, or it is mounted in a tube with spiral movement. By 

 turning the milled head of the pinion, or by turning the objective 



