STAGE-LIGHTS. 121 



night toward the coast would see the light of the light- 

 house like a very brilliant star in the horizon ; but if she 

 should leave her perch and fly a few hundred feet into the 

 air, she would lose sight of it, and she might well wonder 

 what had become of it. The truth would be, that all the 

 light which would naturally have come to that point 

 would have been bent downward near to the surface of 

 the sea, for the benefit of the mariners on the decks of their 

 vessels, leaving the regions of the upper air in darkness, 

 the illumination not being intended for the benefit of the 

 birds. 



There is required, of course, a very bright and concen- 

 trated light for such purposes as this, in order that the 

 necessary amount of illumination may be brought within 

 such a compass that the apparatus within which it is con- 

 tained, and the lenses and reflectors required for throwing 

 all the radiation from it out over the sea, may not be of an 

 inconvenient or unmanageable size. 



A very bright light is also required for the spectral illu- 

 sions exhibited on the stage, which have been described in 

 a former chapter ; for, as it was there explained, it is only 

 a part of the light that falls upon a glass plate that is re- 

 flected from it, and, consequently, any object that is to be 

 seen by reflection must be strongly illuminated. 



This is especially the case when, as has already been ex- 

 plained, a double reflection is required to produce the de- 

 sired effect in the best manner. You will recollect that, 

 by one reflection only, in an inclined glass, objects that are 

 perpendicular in reality are made to appear horizontal. To 

 remedy this difficulty, and bring the image into a right po- 

 sition, a second reflection is necessary. When, in order to 

 reflect this, two plates of glass are used, as shown in the 

 last chapter, a specially bright light is required to supply 

 the necessary quantity for the double reflection. 

 F 



