Gas-Burners , and on , the Illuminating Power of the Gases . IS 
vidness of the combustion, the intensity and whiteness of the light are in- 
creased. 
Some accidental observations, however, led us to imagine, that, although 
the intensity of a given surface is augmented, the increase in this respect is not 
always equivalent to the loss sustained by the diminution of the surface. 
That such is really the fact, will appear from the following experiments. 
In order to augment the vividness of the combustion, various methods 
have been tried for increasing the rapidity of the supply of air. This has been 
effected with regard to Argand burners, either by increasing the diameter of 
the central air-aperture, or by lessening the distance between the flame and 
the glass chimney ; in other words, by contracting the diameter of the chimney. 
Let us therefore consider what will be the effect of the reverse alterations ; 
and, as the simplest mode of diminishing the supply of air, let the central air- 
aperture be contracted. This may be simply done, by bringing the finger 
close under the burner. The flame is then elongated, and although the inten- 
sity of its light is diminished, yet the actual illuminating power is increased. 
The exact increase is indicated by the photometer. But it may be right to 
observe, that the fact is rendered obvious, without the aid of the photometer, 
by the observer turning his back towards the light, and merely attending to 
the difference in the general illumination of the apartment. 
With the view, however, of ascertaining the exact amount of the effect, 
we had little sliders adapted to the bottom of the burners, and graduated to 
50ths of a square inch. If a coal-gas burner, such as is used in Edinburgh, be 
fitted in that manner, and the gas burnt in it with a flame of two inches, it 
will be found, that, as the aperture is diminished by the sliders, the flame be- 
comes taller and taller, and the light greater and greater, till at length the in- 
crease will actually amount to a fourth, a third, or even a half of the origi- 
nal light. 
Thus, when a five-holed Edinburgh coal-gas burner, the air-aperture of 
which has an area of /oths of a square inch, was burnt with a 2-inch flame, 
the light in relation to that of the standard, a jet of 3.2 inches, was as 206 
to 100. But, when the aperture was lessened to ^ths, the flame began to 
elongate; and when only s ^th was left, it was 3 inches long, and its light had 
increased to 266, or by somewhat more than ^th — Again, a 2-inch flame in 
a 10-holed burner gave a light, in proportion to that of the same standard, 
as 452 to 100. When the air-aperture, which is |§ths of a square inch, was 
contracted to s 4 s ths, the flame rose to 3^ inches, and gave 583 of light, or bet- 
ter than a fifth more ; and when the aperture was farther lessened to T | 5 ths, 
the flame was 5 inches long, and the light 665, or nearly a third greater than 
at the beginning. — These experiments were frequently repeated, and some- 
times the increase of the light was even greater. 
If the flame of the burner was originally shorter than 2 inches, the gain 
effected by lessening the supply of air was considerably greater ; and, on the 
other hand, if the flame was originally longer, the gain was less. In the last- 
mentioned burner, a flame of an inch and a half gave nearly double the light, 
when it was lengthened by contracting the air-aperture to 5 2 5 ths of an inch ; 
while a flame originally 4 inches long does not gain at all by such a change. 
