Management of Light in Illumination. 121 



nators directly over the middle of the most elegant 

 billiard-tables, even where he has no reason to sup- 

 pose that the servants into whose hands they come 

 are particularly careful. 



This contrivance, which is extremely simple, can 

 easily be described. The reservoir for the oil, which, 

 as has already been observed, is a flat, hollow ring, has 

 three openings above at equal distances from each 

 other. They are short, vertical brass tubes, of about 

 half an inch in height and three quarters of an inch in 

 diameter internally, which are soldered to the upper 

 part of the reservoir. Each of them is furnished with a 

 brass stopper, which closes it hermetically ; and each 

 of the stoppers is perforated in its axis, and receives a 

 screw of about a quarter of an inch in diameter and 

 three quarters of an inch in length, which by means of 

 a collar of leather closes this aperture completely when 

 the screw is screwed down fast in its place. But these 

 screws are not entire : about one third part of the sub- 

 stance of each of them is filed away, from the shoulder 

 which supports the collar of leather quite down to the 

 lower end of the screw. This neither prevents the 

 screw from moving regularly in the female screw, nor 

 from closing hermetically the opening in the brass 

 stopper when it is screwed down fast in its place ; but, 

 when the screw is turned backwards one or two turns, 

 a passage is opened by which air can pass freely in or 

 out of the reservoir. 



When the illuminator is lighted, a passage for the 

 air to enter the reservoir must be opened by unscrew- 

 ing one of these screws, otherwise the oil cannot flow 

 to the burners ; but at all other times all these screws 

 must be kept screwed fast down, which will most 



