of a common Argand Lamp. 41 



The size and brilliancy of the flame in a common Argand 

 oil lamp depend chiefly upon the shape and dimensions of the 

 glass chimney, and its position in relation to the flame ; but 

 as the contrivances which render the latter more brilliant at 

 the same time diminish its bulk, there is a limit, beyond 

 which we cannot increase the brightness without diminishing 

 the illuminating power; the increase in brilliancy not com- 

 pensating for the diminished bulk of the flame. Sir J. Her- 

 schel has not told us what is the diameter of his Argand 

 burner, or the diameter and form of his glass chimney ; but 

 from the description he has given us of his method of pro- 

 ducing a greatly increased quantity of light, I presume he 

 must have used one of those chimneys which are commonly 

 employed only for gas lamps, being a simple cylinder about 

 nine inches long, and of equal diameter throughout. But this 

 kind of chimney is ill adapted for enlivening a flame, and 

 seems merely to serve for protecting it against currents of 

 air, although, when employed in the manner recommended 

 by Sir J. Herschel, its office is reversed; it becomes a mean of 

 increasing the intensity of combustion, but serves no longer as 

 an efficient protector: and in this latter respect it is imperfect; 

 for admitting the advantages which arise from the increase of 

 light, still these can only be available while a lamp is at rest : 

 the instant it is moved the flame must necessarily impinge 

 against the walls of the chimney, at the great risk of breaking 

 it, and with a certainty of smoking it. But an equal degree of 

 light, and not subject to the inconvenience just mentioned, 

 can be obtained by one of the chimneys ordinarily made use of 

 in the common table lamp, which consists of a base or larger 

 cylinder, upon which the pillar or smaller cylinder is joined 

 by a horizontal part, termed the shoulder: upon the height 

 of the pillar of this chimney, the proportion of its consti- 

 tuent parts to each other and to the burner, and their position 

 in relation to the latter, depend the efficient burning of the 

 lamp. 



And first with reference to the height. The most obvious 

 effect of lengthening a chimney is, to render the flame more 

 flickering and unsteady, at the same time its brightness is 

 slightly increased, and its bulk diminished : the larger the 

 diameter of the chimney compared with the burner, the less 

 marked are these changes. On lengthening a chimney whose 

 pillar had a diameter of 1^ inch, to three feet, and placing it 

 on a lighted lamp, well turned on, whose wick had of an 

 inch diameter, the flame immediately split into several small 

 flickering cones, the largest of which, was not above five or six 

 lines in height ; as the chimney was shortened, so did the 



