of a common Argand Lamp. 4-3 



ness of the flame without diminishing its illuminating power. 

 I am not at present prepared to say where this precise point is ; 

 but I can assert, without fear of contradiction, that an aper- 

 ture of one and one-eighth of an inch diameter, for a lamp 

 whose wick is seven-eighths of an inch, is a size well calcu- 

 lated for giving a great degree of brilliancy to the flame, 

 without materially diminishing its bulk. We come now to 

 the consideration of the best height for placing the plate of 

 tin above the wick of the lamp; this appears to be from two- 

 eighths to three-eighths of an inch, which is that specified 

 by Sir J. Herschel, supposing his burner to have an inch 

 diameter : when we go below this the flame becomes brighter, 

 less coniform, and shorter; the continuity of its circle is inter- 

 rupted ; chasms form in it, producing the appearance of so 

 many distinct flames ; and when the tin has reached the level 

 of the wick, the lamp is well nigh extinguished. Sir J. 

 Herschel, in describing the effect produced on the flame by 

 raising and lowering the chimney, has suggested that it would 

 be an improvement were our common lamps provided with a 

 mechanism for this purpose ; this has actually been done on 

 the continent, and in this country by Mr. Samuel Parker of 

 Piccadilly, the flame of whose hot-oil lamp is regulated en- 

 tirely by raising and lowering the chimney, the wick remain- 

 ing stationary. Now if a number of glass chimneys be made, 

 the diameter of whose pillars shall be the same as those of the 

 apertures in the tin, and these be suspended over the flame with 

 their narrow end downwards, we shall have the same result: 

 but if, instead of this, they be placed in the usual manner on 

 their support, the large end lowermost, we shall still have 

 precisely the same result, provided the commencement of the 

 pillar bear the same position, in reference to the wick, as the 

 upper end did when suspended over it. The diameter of one 

 inch and an eighth, which I have named as a good size for 

 having the pillar of the chimney, is eligible likewise on an- 

 other account : there is less danger of its becoming smoked, 

 to which it would be very liable were it of smaller dimensions 

 than that just specified. The base of the chimney may 

 be an inch and three-quarters or two inches in diameter, and 

 its shoulder should form a right angle with the level of the 

 burner, about half an inch above it. This is a form of chim- 

 ney which I have proved to be well fitted for giving a degree 

 of light very superior to what is seen in Argand lamps having 

 the ordinary sized chimneys. Dr. Ure, in a very interesting 

 paper read before the Institution of Civil Engineers in June 

 last, seems to give the preference to chimneys with rounded 

 shoulders ; these certainly give greater steadiness to the flame, 



