done, while burning it in the ordinary way, to increase
its luminosity; and it is the large surface of flame exposed to the
cooling action of the air which causes this form of burner to give the
lowest service of any per cubic foot of gas consumed. Much is done,
moreover, by faulty fittings and shades, to reduce the already poor
light given out, because the light-yielding power of the flame largely
depends upon its having a well rounded base and broad, luminous zone;
and when a globe with a narrow opening is used with such a flame--as
is done in 99 out of 100 cases--the updraught drags the flame out of
shape, and seriously impairs its light-giving powers, a trouble which
can be got over by having the globe with an opening at the bottom not
less than 4 inches in diameter, and having small shoulders fixed to
the burner, which draw out the flame and protect the base from the
disturbing influence of draughts.

The Argand burner differs from the flat flame burners in that a
circular flame is employed. The air supply is regulated by a
cylindrical glass, and this form of burner gives a better service than
the flat flame burner, as not only can the supply of gas and air be
better adjusted, but the air being slightly warmed by the hot glass
adds to the temperature of the flame, which is also increased by
radiation from the opposite side of the flame itself.

The chief loss of light in such a burner depends upon the fact that,
being circular, the light from the inner surface has to pass through
the wall of flame, and careful photometric experiments show that the
solid particles present in the flame so reduce its transparency that a
loss amounting to about 25 per cent. of light takes place during its
transmission.

The height of the flame also must be carefully adjusted to the size of
the flame, as too long a chimney, by increasing the air supply unduly,
cools, and so lowers the illuminating power of the flame. Experiments
with carbureted water gas gave the following results, with a
consumption of 5 cubic feet per hour:

-----------------------------------------------------
Size of Chimney. | Height of Flame. | Candle Power. |
------------------+------------------+---------------|
6 X 1-7/8 | 2-1/2 | 21 |
7 X 1-7/8 | 2-1/4 | 21.3 |
8 X 1-7/8 | 2-1/8 | 20.8 |
9 X 1-7/8 | 1-7/8 | 18.2 |
------------------+--------