XVJ11 INTRODUCTION. 



Comparison of t*e Different Sources of 

 III u initiation. 



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 



