124 
On Water and Air. 
[February 
century, and he has worked at these subjects and produced 
the most beautiful results from his investigations simply by 
having a good assistant, and directing his assistant to make 
his experiments for him, and to describe the results of those 
experiments. We might occupy a course of ledtures in 
describing the experiments of Plateau. . This experiment 
was devised by him for the purpose of withdrawing the oil 
from the “ pull of gravity/’ as he calls it. A most extra- 
ordinary exhibition of the tendency of drops of water to 
assume this globular form is, I think, to be seen in the 
Fig. 8. 
whirlpool rapids some two or three miles above the Falls o 
Niagara. There you have a stream that drains hall a 
continent. Those rapids are about a hundred yards across, 
and at part of the rapids you have great masses of rock 
on each side. The water impinges upon these masses oi 
rock and waves are formed, and sometimes two waves 
coalesce in the centre of the river. One wave gets upon 
the other, and sometimes the contadt is so violent that the 
crest of the waves is thrown into the air, and these beauti- 
fal water globules are produced. [A photographic view o 
the rapids was thrown upon the screen.] It is, oi course, 
difficult to catch a piaure at the very moment, but you can 
