which makes two things that do not dissolve in each other still hold
together. When you wash your hands, you wet them thoroughly; you take a
little soap to make the adhesion better, and you find your hand remains
wet. This is by that kind of attraction of which I am about to speak. And,
what is more, if your hands are not soiled (as they almost always are by
the usages of life), if you put your finger into a little warm water, the
water will creep a little way up the finger, though you may not stop to
examine it. I have here a substance which is rather porous a column of
salt and I will pour into the plate at the bottom, not water, as it
appears, but a saturated solution of salt which cannot absorb more; so
that the action which you see will not be due to its dissolving anything.
We may consider the plate to be the candle, and the salt the wick, and
this solution the melted tallow. (I have coloured the fluid, that you may
see the action better.) You observe that, now I pour in the fluid, it
rises and gradually creeps up the salt higher and higher; and provided the
column does not tumble over, it will go to the top.
[Illustration: Fig. 1.]
If this blue solution were combustible, and we were to place a wick at the
top of the salt, it would burn as it entered into the wick. It is a most
curious thing to see this kind of action taking place, and to observe how
singular some of the circumstances are about it. When you wash your hands,
you take a towel to wipe off the water; and it is by that kind of wetting,
or that kind of attraction which makes the towel become wet with water,
that the wick is made wet with the tallow. I have known some careless boys
and girls (indeed, I have known it happen to careful people as well) who,
having washed their hands and wiped them with a towel, have thrown the
towel over the side of the basin, and before long it has drawn all the
water out of the basin and conveyed it to the floor, because it happened
to be thrown over the side in such a way as to serve the purpose of a
syphon.[5] That you may the better see the way in which the substances act
one upon another, I have here a vessel made of wire gauze filled with
water, and you may compare it in its action to the cotton in one respect,
or to a piece of calico in the other. In fact, wicks are sometimes made of
a kind of wire gauze. You will observe that this vessel is a porous thing;
for if I pour a little water on to the top, it will run out at the bottom.
You would be puzzled for a good while if I asked you what the state of
this vessel is, what is inside it, and why it is there? The vessel is full
of water, and yet you see the water goes in and runs out as if it were
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