Management of Light in Illuminatiojt. 133 



circular balustrade of cut glass, about an inch in 

 height, round the opening (3 inches only in diameter) 

 at the top of this dome, through which the end of the 

 chimney of the burner passes. 



As this gallery is illuminated by the direct rays of 

 the flame, it produces a beautiful effect, which is the 

 more striking on account of the mild light which is 

 diffused by the luminous dome on which it stands. 



Some of these table illuminators have been con- 

 structed with hemispherical screens below as well as 

 above, which gives them the appearance of a luminous 

 balloon placed on a column and surrounded horizon- 

 tally by a narrow hoop (about half an inch wide, 

 japanned and gilded), the apparent external circumfer- 

 ence of their reservoirs. 



When arranged in this manner, the illuminator is 

 very beautiful, especially when seen at a little distance ; 

 but, for illuminating objects placed on a table, the 

 dome screen is preferable, on account of the shadows 

 of objects being more distinct and better defined when 

 the light is less diffused. 



In examining minute objects, it is always advan- 

 tageous that they should be illuminated by the direct 

 rays which proceed from bodies that are intensely 

 luminous ; but great care must be taken to prevent the 

 eyes being exposed to those rays. No artificial illumi- 

 nation can be so advantageous for nice observations 

 as that of daylight when the sun is high and shines 

 bright ; but nobody in those circumstances can look at 

 the sun with impunity. 



But that kind of illumination which is most favour- 

 able to very distinct vision is not that which is most 

 agreeable ; nor is it the most favourable to the beauty 



