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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