73 
it is not that the drop merely forces itself down under 
the surface, hut in descending carries down with it a 
mass of water which when the ring is 1 inch in diameter 
would be an oblate spheroid having a larger axis of 2 inches 
and a lesser of about 1^ inches. For it is well known that 
the vortex ring is merely the core of the mass of fluid which 
accompanies it, the shape of which is much the same as that 
which would be formed by winding string through and 
through a curtain ring until it was full. 
It is probable that the momentum of these rings corre^ 
spends very nearly with that of the drops before impact, so 
that when rain is falling on to water there is as much motion 
immediately beneath the surface as above it, only the drops, 
so to speak, are much larger and their motion is slower. 
Besides the splash, therefore, and surface effect which the 
drops produce they cause the water at the surface rapidly to 
change places with that at some distance below. 
Such a transposition of water from one place to another 
must tend to destroy wave motion; This may be seen as 
follows. Imagine a la}^er of water adjacent to the sur^ 
face and a few inches thick to be flowing in any direction 
