66 
Proceedings of the Royal Society 
the surface of the water, the following effects are seen. On the 
clean water, the advance of the strip gives rise to a series of very- 
evident and well-marked waves or ripples in front of it, whereas on 
the oily surface no waves are formed. The film is seen simply to 
contract in front of the moving paper. In order to regulate the 
motion of the strips in the different experiments, a convenient 
arrangement is to attach to a pendulum the threads which are fixed 
to the paper strips, and, by drawing the pendulum and strip aside 
to the same amount in each experiment, we can regulate its drag 
on the strip with considerable precision. If we wish to compare 
the effects of equal amounts of energy spent in each case, so as to 
get results corresponding to equal blasts of wind, then the pendulum 
should be light ; and if we wish to see the effects of equal rates of 
motion the pendulum ought to be heavy. 
When we examine the surface of a sheet of water under the 
action of the wind, we observe that the floating bodies on its sur- 
face are all moving forwards— all are carried forwards by a surface 
current, but a closer examination of the smaller bodies lying close 
to the surface shows that the advance of the surface film is a jerky 
one ; one part of the surface advances quickly, then stops, then 
another part gets into rapid movement, and the general appearance 
is that of a patchy and irregular advance of the surface film. With 
oil on the surface all this is changed ; the floating bodies are all 
now seen to be hurrying forward at a nearly uniform rate, the oil 
having entirely checked the patchy and irregular advance which 
gave rise to waves. 
Paradoxical as it may at first sight appear, it is nevertheless true 
that the weakening of the surface film by the oil is a source of 
strength to the surface of the water, and enables it to resist the 
action of the wind. The oil, in fact, makes the surface film inex- 
tensible to small strains, and so regulates the action of the wind 
that waves are prevented, and no effect produced save a nearly 
uniform sliding forward of the surface. 
Supposing the explanation here given to be true as regards the 
formation of small waves or ripples, yet a cause so small seems at 
first sight quite inadequate to explain so wonderful an effect as that 
of oil on a stormy sea, and I can easily imagine the question being 
asked, What effect can this very weak resistance of the surface film 
