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XVJ11 INTRODUCTION. Comparison of t*e Different Sources of III uinitiation. Of course, the brighter the illumination the more satis- factory are magic-lantern projections. Lights are so vari- able that an exact ratio of their relative intensity can hardly be given, and besides, their efficiency cannot be counted in exact proportion to the amount of light given. The Electric light is by far the most intense, but, for the most part, the difficulties at present attending its use practi- cally throw it out of the question. The Magnesium light, though approaching the Lime light in brightness, is too uncertain to be relied on, and its fumes are troublesome. House gas, though well suited for common illumination, lacks the concentration so essential in the lantern Practically the Lime light, variously rated at 100 candles and upward, must mostly be relied on for brilliant public exhibitions. Marcy's lamp gives the brightest flame illumination, but it is not only its amount of light and its intensity, but its advantageous shape, which gives it such remarkable effi- ciency in the Sciopticon Of course the room should be effectually darkened pre- paratory to an exhibition. The apparent brightness of the pictures, however, depend very much on whether the pupil of the eye is more or less dilated. It is safe to say that a person coming to an Oil-light exhibition from the darkness of evening would be as much impressed by it as if coming suddenly from the light of day to witness the effect of lime light. Care should be taken, therefore, to give time for the eye to become accustomed to the darkness, and to prevent dazzling brightness from reaching the spectators from the instrument, or from the white screen, as well as from lights but partially shut off. According to the same principle, passing