LIGHT. 
consequently the-llght, and afford a fuligi- 
nous column, which will pass through the 
centre of the flame, and fly off in the form 
of smoke. The magnitude of the wick may, 
fit)ni time to time, in candles, be reduced, as 
to length,' by snuffing ; but this operation 
will not lemedy the evils which arise from 
too great a diameter. If the oil be not suf- 
ficiently combustible, the ignition will be 
but moderate, and the flame yellow ; and 
the same effect will he produced, if the air 
be not sufficiently jmre and abundant. An 
experiment to this effect may be made by 
including the flame of a small candle or 
lamp in a glass tube of about one inch in 
diameter, standing on the surface of a ta- 
ble. The air which passes between the 
glass and the table, will be sufficient to 
maintain a very bright flame ; but if a me- 
tallic covering, perforated with a hole of 
about a quarter of an inch diameter, be laid 
upon the upper orifice of the tube, the com- 
bustion will be so far impeded, that the 
tiame will be perceptibly yellovvei-. The 
hole may then be more or less closed at 
pleasure by sliding a small piece of metal, 
for example a shilling, over it. The con- 
sequence will be, that the flame will become 
more and more yellow, will at length emit 
smoke, and if the hole be entirely closed, 
extinction will follow. 
Tiie smell arising from the volatile parts, 
which pass off not well consumed from a 
lamp or candle, must be different according 
to tlie nature ot those parts. Tliis depends 
chiefly on the oil, but in some measure upon 
tlie wick. When a candle with a cotton 
wick is blown out, the smell is considerably 
more offensive, than if tlie wick be of linen, 
or of rush ; but less offensive tiian if the 
supply of the combustion had been oil. 
Whenever a candle or lamp is removed, the 
combustion is in some measure impeded by 
the stream of cold air, against which it - 
strikes. Smoke is accordingly emitted from 
its anterior side, and the peculiar smell is 
perceived. From this imperfection, lamps 
are much less adapted to be carried from 
place to place than candles. 
From the necessity of the access of air, 
there will be more light produced from a 
lamp with a number of small wicks, than 
witli one large one, or from a number of 
small candles, than tiie same quantity of 
tallow used to make a single large one. In 
the lamp of Argand, the wick consists of a 
web of cloth in the form of a pipe or tube, 
tlie longitudinal fibres- of which are thicker 
than the circular ones. This is passed by a 
suitable contrivance into a cylindrical cavi- 
ty, which contains the oil ; and there are 
other precautions in the consti uction of the 
apparatus, by which the oil is regularly sup- 
plied, the access of air is duly permitted, 
as well within as without the circle formed 
by the upper edge of this cylindrical wick, 
and this edge can be raised or lowered at 
pleasure. Hence the possessor has it in his 
power to regulate the surface of the wick, 
so that the greatest flame consistent with 
perfect combustion may be produced ; and 
the steadiness of the flame is secured by a 
glass shade or tube, which surrounds it, and 
in a certain degree accelerates the current 
of air. 
In the illumination by candles, wiiere the 
fused matter is contained in a cup or cavity 
of the matter not yet fused, it is of some 
consequence, whetlier the substance be fusi- 
sible at a high or low temperature. The dif- 
ference between wax and tallow candles 
arises from this property. Wax being less 
fusible, will admit of a thinner wick, 'and 
needs no snuffing ; but in a tallow candle 
it is absolutely necessary to have a large 
wick, capable of taking up the tallow as it 
melts. 
The difference of effect in illnmination 
between a thick and a thin wick cannot be 
better shown, than by remarking the ap- 
pearances produced by both. When a can- 
dle with a thick wick is fii st lighted, and 
the wick snuffed short, the flame is perfect 
and luminous, unless its diameter be very- 
great; in which lastcase, there is an opaque 
part in the middle, where the combustion 
is impeded for want of aii-. As the wick 
becomes longer-, the space between its up- 
per extremity and the apex of the flame is 
diminished ; and, consequently, the oil 
which issues from that exti emity, having a 
less space of ignition to pass thronglr, is less 
completely burped, and passes off partly in 
smoke. Ibis evil continues to increase, un- 
til at length the upper extremity of the 
wick pr ojects beyond the flame, and forms 
a sirpport for atr accumulation of soot, 
which is afforded by the imperfect combus- 
tion. A candle in this situation affor-ds 
scarcely one-tenth of the light, which tire 
due combirstion of its materials wotrld pro- 
duce ; and tallow candles, on this account, 
requite continual snutfing. Bnt, on the 
contrary, if we consider the wax candle, we 
find, that as its wick lengthens, the light in- 
deed becomes less, and the enp becomes 
filled with melted wax. The wick, Itow- 
ever, being thin and flexible, does not long 
