LANTERNS AND THEIR MANIPULATION 105 



move it into the exact position. Now and then an operator 

 can do this without the audience perceiving it ; but nearly 

 always the movement in adjusting the slide can be seen after 

 a while, and is very unpleasant. 



No such expedients give sufficient precision for the fine 

 dioramic effects aimed at by the few exhibitors who have a 

 reputation for their exhibitions, as well as for what, apart 

 from this, may be most excellent lectures ; I mean such 

 exhibitions, for instance, as those by Mr. Maiden. Very often 

 in these an ' effect ' must be ' flashed ' on instantly, in most 

 precise position as, for instance, the flashes from the guns 

 in a bombardment, or the sudden change to an explosion. 

 There is only one way to get this. First of all, the two or 

 three lanterns must be precisely centred, by an equal number 

 of precisely similar test- slides kept for the purpose ; three 

 photographs of a diagram showing simply horizontal, perpen- 

 dicular, and diagonal lines all crossing in a common centre, 

 answer admirably. These must be most precisely superposed, 

 so that any one may go into either stage indifferently, and 

 when once centred on the screen, be interchangeable without 

 affecting the precise superposition of the images, when once 

 the stage adjustments are also accurately made. Then every 

 slide must be framed separately, and adjusted in its frame by 

 slips of paper or card, until all the usual ' shake ' or looseness 

 is taken out, and the slide fixed precisely in its frame. Then 

 lastly, if the slips of paper or card, when humoured as far as 

 possible, are not sufficient to adjust it sufficiently, the wooden 

 frame itself is adjusted so as to centre the slide on the screen. 

 Sometimes the frame may need a slip of card stuck on ; or 

 it may need a thin shaving taken off. Now all is certain ; 

 but hours and hours are patiently spent in thus adjusting a 

 set of new slides, before the season really commences. 



The almost microscopic adjustment of the lantern-stages 

 is not so necessary, provided only the slides are always used 

 so that each slide always goes into the same stage. To ensure 



