SCIOPTICON MANUAL. 41 



screw-heads 7J inches apart; the flanges in the rear 

 slide, under two similar screw-heads, holding the instru- 

 ments down, but allowing them to spread till their disks 

 coincide on the screen. 



The construction of the dissolver is shown in Fig. 17, 

 in its three parts. The crescent-shaped dissolver a is 

 mounted on the arm &, as seen in Fig. 16, so as to cover 

 alternately the tubes on It and L, as it swings from side 

 to side. The horizontal part of b slips into c till tho 

 length of the united axle just allows the dissolver to 

 swing clear of the tubes, and the whole is held in place 

 by a socket-spring at each end of the baseboard. 



The dissolver is operated by the handles at c, which 

 are adjusted at the proper angle to limit the lateral 

 movement of a to the distance between tho tubes. 



Light the lamps in their place by reaching the wicks 

 with a lighted match, and attend to them at first to see 

 that they burn steadily and evenly. Focus a picture in 

 .R, for example, while L is covered by tho dissolver, and 



Fig. 17. 



in L while R is covered ; this reduces the disks to equal 

 size on the screen. With tho slides removed, and the 

 dissolver in the position as shown in Fig. 16, spread tho 

 lanterns till the disks coincide. 



DIRECTIONS FOR PRODUCING THE DISSOLVING EFFECTS. 

 With the lanterns lighted, and arranged as shown in 

 Fig. 16, and a slide placed in each, then the gradual 



