alf-filled with port wine the liquid rises a little
up the side of the glass as other liquids do. The wine, however,
contains alcohol and water, both of which evaporate, but the alcohol
faster than the water, so that the superficial layer becomes more
watery. In the middle of the vessel the superficial layer recovers its
strength by diffusion from below, but the film adhering to the side of
the glass becomes more watery, and therefore has a higher
surface-tension than the surface of the stronger wine. It therefore
creeps up the side of the glass dragging the strong wine after it, and
this goes on till the quantity of fluid dragged up collects into a drop
and runs down the side of the glass.

The motion of small pieces of camphor floating on water arises from the
gradual solution of the camphor. If this takes place more rapidly on one
side of the piece of camphor than on the other side, the surface-tension
becomes weaker where there is most camphor in solution, and the lump,
being pulled unequally by the surface-tensions, moves off in the
direction of the strongest tension, namely, towards the side on which
least camphor is dissolved.

If a drop of ether is held near the surface of water the vapour of ether
condenses on the surface of the water, and surface-currents are formed
flowing in every direction away from under the drop of ether.

If we place a small floating body in a shallow vessel of water and wet
one side of it with alcohol or ether, it will move off with great
velocity and skim about on the surface of the water, the part wet with
alcohol being always the stern.

The surface-tension of mercury is greatly altered by slight changes in
the state of the surface. The surface-tension of pure mercury is so
great that it is very difficult to keep it clean, for every kind of oil
or grease spreads over it at once.

But the most remarkable effects of change of surface-tension are those
produced by what is called the electric polarization of the surface. The
tension of the surface of contact of mercury and dilute sulphuric acid
depends on the electromotive force acting between the mercury and the
acid. If the electromotive force is from the acid to the mercury the
surface-tension increases; if it is from the mercury to the acid, it
diminishes. Faraday observed that a large drop of mercury, resting on
the flat bottom of a vessel containing dilute acid, changes its form in
a remarkable way when connected with one of t