148 Management of Light in Illumination. 



it by a long narrow tube, which perhaps may be some- 

 times obstructed, more or less, by small parcels of oil 

 that may remain in it. 



As this accident was found to happen sometimes, 

 another contrivance was used to facilitate the escape 

 of this air, which has been found to answer perfectly. 



A small hole of about three twentieths of an inch in 

 diameter, which is represented in the figure, has been 

 made through the side of the vertical brass tube s^ and 

 opening directly into the cavity of the secondary reser- 

 voir. As the air in this reservoir can escape freely 

 through this opening, there is no longer any difficulty 

 whatever in filling the lamp with oil ; and when this 

 operation is ended, as the hole by which the air es- 

 capes out of the secondary reservoir is hermetically 

 closed by the brass stopper, as may be seen in the 

 figure, no inconvenience whatever has resulted from 

 the use of this contrivance. 



We will now suppose that the lamp, after having 

 been filled, is lighted. 



The oil, passing continually through the small open- 

 ing in the side of the cylinder b, will flow through the 

 tube/ into the burner. 



As the oil in the circular reservoir passes freely into 

 the burner, so that in the secondary reservoir passes 

 freely into the circular reservoir, through the small 

 square trunk, open at both ends, which is fixed down 

 on the bottom of the secondary reservoir, so that the 

 lamp will continue to burn till the last drop of oil is 

 consumed. 



It is very certain that the oil in the secondary reser- 

 voir would not flow freely out of it into the circular 

 reservoir if air could not at the same time enter it 



