Management of Light in Illumination. 131 



structed on Argand's principles. It is fixed in a verti- 

 cal position in the axis of a larger cylinder, which is 

 1.88 inch in diameter and 5.8 in length, in the opening 

 of which above the glass chimney is fixed. The lower 

 part of this cylinder enters 1.5 inch within the column, 

 and is firmly attached to it by means of a projecting 

 metallic knob, situated on the inside of the column 

 near its upper extremity. A vertical slit or opening, 

 on one side of the cylinder, about a quarter of an inch 

 wide and an inch and a quarter long, permits the cylin- 

 der to enter the column, notwithstanding its projecting 

 knob ; and when the cylinder has been forced down 

 into the column so low that this knob comes to strike 

 against the upper part of this vertical opening, on turn- 

 ing round the cylinder, the column being held fast, 

 the knob is forced into a horizontal opening, by which 

 means the cylinder and the column are locked to- 

 gether, in a manner similar to that employed for fixing 

 a bayonet to its musket. This horizontal opening in 

 the side of the cylinder, into which the knob passes 

 in fastening the cylinder to the column, may be about 

 one inch in length ; and, instead of making it every- 

 where of the same width, it will be best to make it a 

 little narrower towards its extremity, in order that the 

 knob may fill it completely in that part, and on being 

 forced into it, like a wedge, may hold the faster. 



As it will seldom be found necessary to separate the 

 . reservoir from its stand (once a month, perhaps, just 

 to pour out any small quantity of oil that may have 

 leaked out of the burner and fallen down into the 

 column), it will be very desirable that the reservoir 

 should be fixed to the column in the most solid man- 

 ner, in order to prevent their being separated by any 

 accident, while the illuminator is in use. 



