61 
of Ediiiburgli, Session 1882-83. 
apart, at right angles to the direction of the wind. These floats 
were allowed to drift to the opposite end of the pond to see that 
the rate of motion was the same at both sides. Some oil was now 
poured over the water at one side, and other two floats started over 
the same routes as the first two. It was found that the two floats 
still travelled at the same rate, that oiling had not perceptibly 
altered the rate of motion. We might almost have expected a 
different result, on account of the waves on the clean water affording 
a better catch to the wind, but possibly this advantage might be lost 
by the eddies and irregular motions resulting from the waves. 
I do not place any great reliance on the accuracy of these experi- 
ments, and the last one is evidently on too small a scale j yet I think 
if the effect of oil on troubled waters is due to its reducing the grip 
of the wind, the reduction would require to be very great, so great 
that there would have been, some evidence of it even in these 
imperfect experiments. 
There is, however, another consideration which indicates that the 
oil does not produce its effects by reducing the friction between the 
air and the surface of the water. Oil itself when exposed to wind 
is driven into waves very much as water is. It may be that the 
waves are not so marked in oil as in water, but this is chiefly due 
to the greater viscosity of the oil. This -was seen in some experi- 
ments made on a small scale for the purpose of observing the effect 
of wind on a body of oil. For this purpose two shallow vessels 
about half a metre square were placed in an exposed part of a field, 
where the wind could blow freely over them. One vessel was filled 
with oil, and the other with water as a standard with which to 
compare the movements of the oil. It was observed that if the oil 
was thick and viscous there was but little effect, and scarcely any 
surface circulation produced ; and it required a strong breeze to 
drive the oil into waves. But with paraffin oil, which is thin and 
mobile, the result was very different ; it seemed more easily driven 
into waves than even water. This was probably due to the oil 
having a less specific gravity than the water, but I think the com- 
paratively greater agitation observed in the oil was partly owing to 
the water surface not being quite clean, on account of the paraffin 
vapour which could not easily be prevented from condensing upon 
it, so that the water was not so easily driven into waves as it ought 
