Even from the early days of the magic lantern projectionists experimented with special effects. Coloured pieces of glass were placed in front of the image to modify the picture as it was being projected. It was soon realised that having to matching pair of lanterns made it possible to project one image on top of another or dissolve one image into another.
This lantern is called a "biunial" (two in one) it was a precision instrument used to create startling special effects on the screen. With such an apparatus one slide could be made to dissolve into another creating startling effects (e.g. day becoming night etc). Even more complex results could be achieved with a "triunial" ( three in one lantern)
Above a matching pairr of dissolving view effect slides of "Summer & Winter." Dissolving views could be used to make one picture subtly change into another or superimpose one image on top of another to add drama to a show ( for example the appearance of angels). Click the play button to see dissolving view effect
A tri-unial ( three in one ) lantern. With this device all sorts of sophisticated special effects could be created