of Edinhurgli, Session 1882-83. 
63 
instead of supposing the wind to act at only one place, we consider 
what actually takes place in nature, namely that the wind strikes 
the surface of the water at all points, hut more strongly at some points 
than at others, on account of the eddies produced in the air in its 
passage over the resisting water, it is evident under these conditions 
that certain parts of the surface film are more powerfully urged for- 
wards than others, and the water yielding to this unequal action is 
driven into a series of waves, having a gradually accumulating effect. 
This effect is intensified by one side of the wave being thrown up 
into such a position that the wind acts more powerfully on it than 
on the other side, or than on a horizontal surface. 
Let us now look at the action of the same water surface, hut over 
which there has been thrown a film of oil. The surface has 
entirely changed its character. New free surface or film cannot 
now he developed without the expenditure of energy. If we try 
to move forwards one part of the surface, we find its motion is 
resisted by the tension of the surface behind it increasing on 
account of the removal of the oil, and the tension in front of the 
moving area does not increase hut diminishes. The forward move- 
ment of the film is therefore checked. Suppose now the wind to ' 
blow over such a surface, the parts where the wind strikes strongest 
will tend to move forwards, hut will he unahle to do so on account 
of the increasing tension behind and reduced tension in front. 
Further, the parts upon which the wind strikes least are drawn for- 
wards by the greater tension in front of them and behind the parts 
tending to move most quickly, and where the wind has developed 
an increased surface tension. The result of this is, that the wind 
cannot drive forwards isolated patches of film or surface so as to 
cause waves, but the whole of the surface is caused to advance at 
nearly a uniform rate, and the formation of waves is thereby pre- 
vented. 
In illustration ' of these points the following experiments were 
shown * — Two large shallow rectangular vessels with parallel sides 
were prepared. Both vessels were filled with water, and over the 
surface of one was put a little oil, the other being kej3t clean. 
Narrow strips of paper, about 2 or 3 cm. broad, were cut to such a 
length that they would when expanded by the water be slightly 
shorter than the breadth of the vessels. One of these strips of 
