hen both the experiments
with the wet brush and with the water-drop will be explained.

Let us therefore try another experiment to see whether in other ways
water behaves as if it had an elastic skin.

I have here a plain wire frame fixed to a stem with a weight at the
bottom, and a hollow glass globe fastened to it with sealing-wax. The
globe is large enough to make the whole thing float in water with the
frame up in the air. I can of course press it down so that the frame
touches the water. To make the movement of the frame more evident there
is fixed to it a paper flag.

Now if water behaves as if the surface were an elastic skin, then it
should resist the upward passage of the frame which I am now holding
below the surface. I let go, and instead of bobbing up as it would do if
there were no such action, it remains tethered down by this skin of the
water. If I disturb the water so as to let the frame out at one corner,
then, as you see, it dances up immediately (Fig. 4). You can see that
the skin of the water must have been fairly strong, because a weight of
about one quarter of an ounce placed upon the frame is only just
sufficient to make the whole thing sink.

This apparatus which was originally described by Van der Mensbrugghe I
shall make use of again in a few minutes.

[Illustration: Fig. 4.]

I can show you in a more striking way that there is this elastic layer
or skin on pure clean water. I have a small sieve made of wire gauze
sufficiently coarse to allow a common pin to be put through any of the
holes. There are moreover about eleven thousand of these holes in the
bottom of the sieve. Now, as you know, clean wire is wetted by water,
that is, if it is dipped in water it comes out wet; on the other hand,
some materials, such as paraffin wax, of which paraffin candles are
made, are not wetted or really touched by water, as you may see for
yourselves if you will only dip a paraffin candle into water. I have
melted a quantity of paraffin in a dish and dipped this gauze into the
melted paraffin so as to coat the wire all over with it, but I have
shaken it well while hot to knock the paraffin out of the holes. You
can now see on the screen that the holes, all except one or two, are
open, and that a common pin can be passed through readily enough. This
then is the apparatus. Now if water has an elastic skin which it
requires force to stretch, it ought not to run through these holes very
readily; it ought no