If the shutter of the first lamp is now closed, and that of the second opened, the audience will see only the postcard at the back, set in a frame of dead black.
The exhibitor should then slowly press down the shutter of the second lamp, and simultaneously raise that of the first. The serrations—in one case gently cutting off the light, and in the other permitting it to stream forth gradually—will have the effect of making one postcard slowly dissolve from view, and give place to the reflection of the other.
The back of the show being in complete darkness, the glass acts as a perfect mirror, and whilst the audience are gazing at the reflection of the first card, a fresh view may be substituted for that at the back, without their being aware of the change.
Having accomplished this, the showman must uncover the second lamp and push down the shutter of the first. The result will be that the reflected view fades from sight, and the fresh picture postcard is displayed.
It is then a simple matter to slip the card already used from its position between the glass and stage front, and insert another in its place.
In this manner a succession of views may be made to dissolve into one another.
As has already been mentioned, there is no limit to the dimensions of such a show—the showman being guided by the size of the pictures he is able to obtain. Picture postcards are always procurable, and no difficulty should be experienced in obtaining slightly larger views from magazines, art catalogues, &c.
Of course, in the very large shows a much brighter light is required, and four lamps must be used instead of two.