18 Drs Christison and Turner on the Construction of 
experiments, so far as we know, yet published, which are obviously exempt 
from this source of error, are those of Mr Brande. He has detailed the par- 
ticulars of them minutely, and expressly mentions that the flames were burnt 
with their full intensity, short of the production of smoke. It will presently 
be seen, ^however, that this was done without his being aware of its import- 
ance, (Phil. Trans. 1820, p. 22.) 
Another inference that may be drawn from the effect of the length of the 
flame upon its light, is, that the ordinary mode of altering the flame of gas- 
burners according to the quantity of light required, is very far from being eco- 
nomical. For each burner there is but one height of flame which is economi. 
cal ; and if it be lessened by reducing the supply of gas, the saving is by no 
means proportional to the diminution of the light. For example, if the flame of 
a 5 -holed coal-gas burner be reduced from its ordinary elevation of 3 inches to 
half an inch, the light is diminished to a seventh part, but the expenditure to 
a third only. In order, then, to have an economical expenditure, with diffe- 
rent quantities of light, which many consumers would desire, different burn- 
ers should be used, or the burner should be supplied with some simple piece 
of mechanism, for cutting off the central supply of air as the flame is short- 
ened. It must be obvious, however, that the customers of a public company, 
and even those who make gas for their own use on a small scale, cannot con- 
veniently burn it in any burner with the highest and most favourable eleva- 
tion of flame. For if that was done, a slight movement of the glass-chimney, 
or agitation of the surrounding air, or increase in the flow of the gas, would 
cause the flame to smoke. 
2. We shall now pass to the consideration of the various points in the con- 
struction of the Burners, which influence the light given out by the gases. 
And the first in order is the diameter of the jet-holes. 
Iieasoning from the principles formerly laid down regarding the most eco- 
nomical way of burning the gases, it will be inferred, that, in a single jet, the 
diameter of its aperture ought to be such as to insure the complete combus- 
tion of the gas, but not to render it more vivid than is necessary for that ef- 
fect. If the hole is too large, the combustion will be incomplete, because the 
flame will be wide, and the surface exposed to the air disproportionately small ; 
the charcoal proceeding from the decomposition of the gas will either not burn at 
all, or burn faintly, and in consequence the jet will smoke or have a brown co- 
lour. If, on the contrary, the hole is very small, the flame, which corresponds 
with it, will have a proportionally large surface exposed to the air, and, in 
consequence, burn too vividly, and without previous decomposition of the gas. 
Accordingly, if oil-gas is burnt through a coal-gas jet-burner, which is com- 
monly a 28th of an inch in diameter, its flame is brown, and light feeble ; and 
if coal-gas be burnt through an oil-gas jet, which varies in diameter from a 
45th to a 60th, its flame, though very white about the middle, gives less light 
than in its own jet, and has a long base of a blue colour, which is always pre- 
sent when the combustion is too vivid. 
The diameter best fitted for single jet-burners appears to be about a 28th 
of an inch for coal-gas, and a 45th for oil-gas. We have not yet made any 
very accurate experiments on this point with respect to coal-gas : but, cer- 
