RAIN-DROPS ON THE SEA. 



Ill 



water the splash or rebound is visible enough, as are also the waves 

 which diverge from the point of contact ; but the effect caused by the 

 drop under the surface is not apparent, because, the water being all 

 of the same color, there is nothing to show the interchange of place 

 which may be going on. There is, however, a very considerable effect 

 produced. If instead of a drop of rain we let fall a drop of colored 

 water, or, better still, if we color the topmost layer of the water, this 

 effect becomes apparent. We then see that each drop sends down 

 one or more masses of colored water in the form of vortex rings. 

 These rings descend with a gradually diminishing velocity and with 

 increasing size to a distance of several inches, generally as much as 

 eighteen, below the surface. Each drop sends in general more than 

 one ring, but the first ring is much more definite, and descends much 

 quicker than those which follow it. If the surface of the water be not 

 colored, this first ring is hardly apparent, for it appears to contain 



Drops descending below the Surface. 



Very little of the water of the drop which causes it. The actual size 

 of these rings depends on the size and speed of the drops. They 

 steadily increase as they descend, and before they stop they have 

 generally attained a diameter of from one to two inches, or even 

 more. The diagram above shows the effect which may be produced 

 in a glass/vessel. It is not that the drop merely forces itself down 

 under the surface, but, in descending, cai'ries down with it a mass of 

 water which, when the ring is one inch in diameter, would be an oblate 

 spheroid, having a larger axis of two inches and a lesser of about one 

 and a half inch. 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 



