Vlll INTRODUCTION. 



give access to the interior of the instrument and for vari- 

 ous experiments. It can be drawn forward to suit a lens 

 of longer focus. Its hood hides reflected and diffused light, 

 and allows space for curtain and tinters. 



11. The Sciopticon Curtain. Turning the 

 milled head at either side, gives the appearance upon the 

 screen of a curtain rising, or falling, thus handsomely open- 

 ing or closing an exhibition. It may also be temporarily 

 closed at any time, to allow the attention to be directed to 

 other exercises. 



The process of changing the pictures may be hidden 

 from view by shutting off the light with the left hand ; then 

 pushing the out-going picture into the left hand by sliding 

 another into its place with the right ; and then flashing on 

 the light with the right hand ; all of which may be sooner 

 done than said. In any change of programme the awk- 

 wardness of showing the " full moon," or the disk without 

 a picture, may always be avoided by using the opaque cur- 

 tain. 



This curtain also serves as a back cap for the objective, 

 protecting the back lens from dust and light when not in 

 use, as the front cap protects the front lens. 



12. The Sciopticon Tinters. The tinting-glasses 

 are drawn up close behind the objective lens by means of 

 rods terminating in knobs above. This lets the color down 

 upon the screen, not with a sharp outline like the curtain, 

 but with a gradual shading. With the blue tint partially 

 drawn, this property gives to plain photographs of scenery 

 a blue sky, shading off without abruptness down to the 

 horizon. Slightly drawing up the blue, then the red, and 

 then turning the button attached to the opaque curtain a 

 little, fades away gradually the upper portion of the disk, 



