123 OPTICAL PROJECTION 



already hinted. A common addition to the better class is what 

 is called a ' curtain-slide ' of brass. This is a single brass 

 shutter passing through both stages, and so adjusted (by 

 screws) that just as much is shown on one disc up to a sharp 

 edge, as is covered on the other. When raised or lowered, 

 the effect is as if one picture pushed the other up or down. 

 With statuary, a slide representing a curtain is used in one 

 lantern, while the shutter draws up to reveal the statue. Or 

 a curtain-slide is often used thus at the beginning and end of 

 an exhibition. 



The other usual effects fitted to this class of lanterns are 

 ' flash -shutters ' and * tinters.' The first is a shutter of brass 

 over the front of each objective, to shut off a lantern suddenly, 

 or open suddenly, when the light is full on. Many dioramic 

 effects, such as an explosion in a bombardment scene, must 

 be ' flashed ' on instantaneously to have any effect ; a ' bang ' 

 being made in some way at the same time, for which a large 

 gong does very well. Occasionally an axle is fixed between 

 the two nozzles, on which revolve two arms with a shutter at 

 the end of each, which can be moved out of the way when 

 not required, but are adjusted to give the required ' flash ' 

 before the scene comes on. Personally (my experience being, 

 however, very small, and quite as an amateur in these 

 matters), I prefer to trust to the hand alone, held in front 

 of the nozzle before the light is turned on, and which can be 

 withdrawn in an instant, and with no risk of failure. 



Tinters may add very much to the pleasing effect of plain 

 photographs, if used with suitable subjects. Thus, a warm 

 tint is easily thrown over a foreground, and a blue tint over 

 the sky, or sea and sky, or on a moonlight scene. Tinters 

 are of two kinds. Fig. 68 shows the most common. It fits 

 on the nozzle of the objective, and any different colours can 

 be fitted in the top and bottom shutters, while an opaque 

 shutter outside can also be folded down, so as to gradually 

 extinguish the picture altogether. 



