Fig. 66 will show the way in which these changes are managed. The large picture, which is hanging vertically, is painted both in front and behind. The front is illuminated by reflection from a semi-transparent screen placed over it, which receives the light of the floor above. The back is lighted from the windows behind, which are provided with blinds to regulate the amount of light. The effects produced by the diorama were truly marvellous, and Daguerre had a special talent for this kind of painting. His famous _Midnight Mass_, which was exhibited at the Regent’s Park, was one of the most renowned of his works. The scene first represented a dark, empty church, feebly lighted by a small altar lamp, but gradually the lights appeared here and there, worshippers congregated in front of the altar, filling the nave and aisles. In Paris the same scene was exhibited, representing the interior of the Church of St. Germain l’Auxerrois with such perfect reality, that a countryman actually threw a halfpenny against the painted canvas, to see whether he were really in a church or not. The next scene represented the destruction of the village of Goldau, near Lucerne, by a landslip. First there appeared a smiling fertile valley, its sides crowned with verdure; a storm gradually rose, the rain fell, the wind blew, the lightnings flashed, and the thunder rolled in the distance. Darkness at last closed in, and when the sun once more rose over the valley, nothing was to be seen but a mass of fallen rocks. ------------------------------------------------------------------------ CHAPTER VII. THE STEREOSCOPE.