he strength of the skin of alcohol and of water, or
of water containing much or little alcohol, gives rise to a curious
motion which you may see on the side of a wine-glass in which there is
some fairly strong wine, such as port. The liquid is observed to climb
up the sides of the glass, then to gather into drops, and to run down
again, and this goes on for a long time. This is explained as
follows:--The thin layer of wine on the side of the glass being exposed
to the air, loses its alcohol by evaporation more quickly than the wine
in the glass. It therefore becomes weaker in alcohol or stronger in
water than that below, and for this reason it has a stronger skin. It
therefore pulls up more wine from below, and this goes on until there is
so much that drops form, and it runs back again into the glass, as you
now see upon the screen (Fig. 14). There can be no doubt that this
movement is referred to in Proverbs xxiii. 31: "Look not thou upon the
wine when it is red, when it giveth his colour in the cup, when it
moveth itself aright."

If you remember that this movement only occurs with strong wine, and
that it must have been known to every one at the time that these words
were written, and used as a test of the strength of wine, because in
those days every one drank wine, then you will agree that this
explanation of the meaning of that verse is the right one. I would ask
you also to consider whether it is not probable that other passages
which do not now seem to convey to us any meaning whatever, may not in
the same way have referred to the common knowledge and customs of the
day, of which at the present time we happen to be ignorant.

[Illustration: Fig. 14.]

Ether, in the same way, has a skin which is weaker than the skin of
water. The very smallest quantity of ether on the surface of water will
produce a perceptible effect. For instance, the wire frame which I left
some time ago is still resting against the water-skin. The buoyancy of
the glass bulb is trying to push it through, but the upward force is
just not sufficient. I will however pour a few drops of ether into a
glass, and simply pour the vapour upon the surface of the water (not a
drop of _liquid_ is passing over), and almost immediately sufficient
ether has condensed upon the water to reduce the strength of the skin to
such an extent that the frame jumps up out of the water.

There is a well-known case in which the difference between the strength
of the