The Chemical History of a Candle | Page 7

of the flame
as you see it under the glass shade. It is steady and equal; and its
general form is that which is represented in the diagram, varying with
atmospheric disturbances, and also varying according to the size of the
candle. It is a bright oblong--brighter at the top than towards the
bottom--with the wick in the middle, and besides the wick in the
middle, certain darker parts towards the bottom, where the ignition is
not so perfect as in the part above.
[Illustration: Fig. 3.]
I have a drawing here, sketched many years ago by Hooker, when he
made his investigations. It is the drawing of the flame of a lamp, but it
will apply to the flame of a candle. The cup of the candle is the vessel
or lamp, the melted spermaceti is the oil, and the wick is common to
both. Upon that he sets this little flame, and then he represents what is
true--a certain quantity of matter rising about it which you do not see,
and which, if you have not been here before, or are not familiar with
the subject, you will not know of. He has here represented the parts of
the surrounding atmosphere that are very essential to the flame, and
that are always present with it. There is a current formed, which draws
the flame out--for the flame which you see is really drawn out by the
current, and drawn upward to a great height--just as Hooker has here
shewn you by that prolongation of the current in the diagram. You may
see this by taking a lighted candle, and putting it in the sun so as to get
its shadow thrown on a piece of paper. How remarkable it is that that
thing which is light enough to produce shadows of other objects, can be
made to throw its own shadow on a piece of white paper or card, so that
you can actually see streaming round the flame something which is not
part of the flame, but is ascending and drawing the flame upwards.
Now, I am going to imitate the sunlight, by applying the voltaic battery
to the electric lamp. You now see our sun, and its great luminosity; and
by placing a candle between it and the screen, we get the shadow of the
flame.
[Illustration: Fig. 4.]
You observe the shadow of the candle and of the wick; then there is a

darkish part, as represented in the diagram, and then a part which is
more distinct. Curiously enough, however, what we see in the shadow
as the darkest part of the flame is, in reality, the brightest part; and here
you see streaming upwards the ascending current of hot air, as shewn
by Hooker, which draws out the flame, supplies it with air, and cools
the sides of the cup of melted fuel.
I can give you here a little further illustration, for the purpose of
shewing you how flame goes up or down; according to the current. I
have here a flame--it is not a candle flame--but you can, no doubt, by
this time, generalise enough to be able to compare one thing with
another. What I am about to do is to change the ascending current that
takes the flame upwards into a descending current. This I can easily do
by the little apparatus you see before me. The flame, as I have said, is
not a candle flame, but it is produced by alcohol, so that it shall not
smoke too much. I will also colour the flame with another substance[6],
so that you may trace its course; for with the spirit alone you could
hardly see well enough to have the opportunity of tracing its direction.
By lighting this spirit-of-wine, we have then a flame produced; and you
observe that when held in the air, it naturally goes upwards.
[Illustration: Fig. 5]
You understand now easily enough why flames go up under ordinary
circumstances--it is because of the draught of air by which the
combustion is formed. But now, by blowing the flame down, you see I
am enabled to make it go downwards into this little chimney--the
direction of the current being changed. Before we have concluded this
course of lectures, we shall shew you a lamp in which the flame goes
up and the smoke goes down, or the flame goes down and the smoke
goes up. You see, then, that we have the power in this way of varying
the flame in different directions.
There are now some other points that I must bring before you. Many of
the flames you see here vary very much in their shape by the currents
of air blowing around them in different directions; but we can, if we
like, make