50 ’ CAPILLARY RIPPLES. 
brilliant and striking manner. For instance, the weight of the wire 
used is so small in comparison with the strength of the electric current 
sent through it that nothing else can compare with it in this 
respect. The result is that if you bring an ordinary bar magnet as 
near as a foot even the magnetic force that would not be sufficient to 
affect an ordinary suspended wire carrying the current will at once lift 
the wire up into an arch, or make it twist or move in a most agile and 
brilliant manner. This experiment was described for the first time in 
France this year, and was published in the autumn, and when it 
succeeds it isa most brilliant and beautiful experiment. (After two 
failures the experiment succeeded). (Applause). 
One might show a great number of exceedingly striking experiments 
to illustrate the existence of surface tension, but these two I hope are 
sufficient to make it evident that a liquid surface is an elastic surface 
which resists being stretched. 
Now let me after this introduction come to the case of ordinary waves 
at sea. If you take the case, which is only too familiar to many of us, 
of a great swell on the ocean with waves a quarter of a mile perhaps, 
or even more, travelling at a speed which no ship can hope to keep 
pace with, as those waves come along the actual slope of the waves is 
nothing at all considerable, but they travel at an enormous speed, the 
larger the wave is the more quickly it travels. Large waves of any 
- fluid, whether quicksilver or water or of anything else, all travel at 
exactly the same speed, because just in proportion as the amount of 
~ matter in the wave is less with the lighter material so is the force due to 
_ gravity upon it less, and it is in virtue of the gravitational force that 
the propagation of the wave is continued. What is the law which 
connects the wave with the velocity with which it travels? This 
has been calculated over and over again and there is no difficulty 
‘ about it, and it has been experimentally observed as much as fifty 
years ago by Mr. Scott Russell with waves of all sizes, and the 
law is this: that if you take a wave four times as long as another from 
~ crest to crest (I am not speaking of the height of waves, because the 
height has nothing to do with it) it will travel twice as fast; 
if it is nine times as long it will travel three times as fast, and so on; 
and if you want to know the actual speed with which a wave of any 
~ gize will travel that can be made evident by means of a diagram like 
the one here upon the wall, which gives upon ita large amount of 
other information. This is not an ordinary diagram divided up into 
squares of equal parts, it is a logarithmic chart.’ In order to find the 
_ case of a wave of any wave length it is necessary to move along one of 
the horizontal lines until the number representing the wave length in 
inches ig reached. Then on travelling up a vertical line until the 
“velocity line” is reached the corresponding number on the vertical 
scale gives the velocity in inches a second. Similarly where the 
frequency line is cut the vertical scale gives the number of waves which 
pass any point in a second. For gravitational waves these lines are 
straight and slope up and down respectively at angles whose tangents 
1 For further particulars of the logarithmic chart and of the use of “scale lines ”” thereon, see 
‘* Nature,” 18th July, 1895. 
