But the iron wire, which you burnt in oxygen gas, appeared to me to emit
flame; yet, as it was a simple metal, it could contain no hydrogen?

MRS. B.

It produced a sparkling dazzling blaze of light, but no real flame.

EMILY.

And what is the cause of the regular shape of the flame of a candle?

MRS. B.

The regular stream of hydrogen gas which exhales from its combustible
matter.

CAROLINE.

But the hydrogen gas must, from its great levity, ascend into the upper
regions of the atmosphere; why therefore does not the flame continue to
accompany it?

MRS. B.

The combustion of the hydrogen gas is completed at the point where the
flame terminates; it then ceases to be hydrogen gas, as it is converted
by its combination with oxygen into watery vapour; but in a state of
such minute division as to be invisible.

CAROLINE.

I do not understand what is the use of the wick of a candle, since the
hydrogen gas burns so well without it?

MRS. B.

The combustible matter of the candle must be decomposed in order to
emit the hydrogen gas, and the wick is instrumental in effecting this
decomposition. Its combustion first melts the combustible matter,
and . . . .

CAROLINE.

But in lamps the combustible matter is already fluid, and yet they also
require wicks?

MRS. B.

I am going to add that, afterwards, the burning wick (by the power of
capillary attraction) gradually draws up the fluid to the point where
combustion takes place; for you must have observed that the wick does
not burn quite to the bottom.

CAROLINE.

Yes; but I do not understand why it does not.

MRS. B.

Because the air has not so free an access to that part of the wick which
is immediately in contact with the candle, as to the part just above, so
that the heat there is not sufficient to produce its decomposition; the
combustion therefore begins a little above this point.

CAROLINE.

But, Mrs. B., in those beautiful lights, called _gas-lights_, which are
now seen in many streets, and will, I hope, be soon adopted every where,
I can perceive no wick at all. How are these lights managed?

MRS. B.

I am glad you have put me in mind of saying a few words on this very
useful and interesting improvement. In this mode of lighting, the gas is
conveyed to the extremity of a tube, where it is kindled, and burns as
long as the supply continues. There is, therefore, no occasion for a
wick, or any other fuel whatever.

EMILY.

But how