PROGRESS IN ARTIFICIAL LIGHTING. 611 
gases alone. Its illuminating power is very feeble. The feeble illuminosity of 
the Bunsen flame appears to be due to a number of causes. We have, first, a 
rapid oxidation of luminiferous material to gases of feeble illuminating power by 
the oxygen in the admixed air; in the second place, we have the presence of 
diluted gases, which, of themselves, reduce the illuminating power; and, thirdly, 
we have heat withdrawn by the indifferent gases, as nitrogen, and the products 
of combustion, carbon dioxide and water. 
We cannot say that the loss of luminosity is due to any one of these 
causes acting singly. On the other hand, in consequence of the more perfect 
combustion that takes place, it is used as a heat-producing flame and its temper- 
ature can be still further raised by a short conical chimney, supported on six 
metal arms arranged in the form of a star. If a solid body be introduced into 
this feebly luminous flame, such, for instance, as a piece of a platinum wire, the 
incandescent metal glows with a brilliant light, and, inasmuch as it is smokeless, 
it will not act destructively on the platinum in the same manner as a smoky gas 
flame will do. The luminosity of a Bunsen burner can be restored by shutting 
off the entry of air, either by closing the holes with the finger or by the rotation 
of a slide which covers them. The light then becomes much more brilliant, with 
abundant formation of smoke. 
The flames of candles and lamps, whether the substance burned be tallow 
or wax, rape oil or petroleum, do not differ essentially from that of an ordinary 
gas burner. The same hydrocarbon which is the essential constituent of com- 
mon gas is the source of light to them. The hot wick which draws up the fluid 
material about to be burned plays the part of a small gas factory, the produce of 
which is used on the spot, the only difference being that coal gas is always puri- 
fied before it is consumed, whereas the extemporaneous gas of a candle or lamp 
is consumed without being purified at all. On the other hand, the tallow, wax 
and oil contain the carbon and hydrogen in a purer and more concentrated form 
than the coal from which ordinary coal gas is made. The flames of candles and 
of lamps all owe their luminosity to the incandescence of particles of carbon 
floating in them, and the reason why one description of candle or lamp is more 
smoky than another is because the supply of air in the smoky one is not suffi- 
cient to produce adequate combustion. 
A petroleum lamp burns, in the first instance, with a dull, murky flame, 
giving off a large quantity of smoke, but it acquires a high degree of luminosity 
when the glass chimney is applied, for the presence of the chimney causes a 
strong draft, supplying the air requisite for the thorough combustion of the gas 
with which it was previously intermingled. The brilliancy of a petroleum flame 
is thus materially exalted by an increased supply of air, while that of a Bunsen 
burner, as has just been seen, is almost abolished by the same means. The 
contrary effects observed in these two cases admit of an easy explanation. In 
the latter instance, the amount of air supplied is so great that scarcely any of that 
separation of the particles of carbon takes place which is so necessary in order 
that a bright hght should be produced. But in a petroleum lamp the introduc 
