ON VORTEX MOTION. 
281 
of fluid motion was now evident. Any irregular solid moving 
through the water must from its angles send off lines of vortices 
such as those behind the oblique vane. As we move about we 
must be continually causing vortex rings and vortex bands in 
the air. Most of these will probably be irregular, and re- 
semble more the curls in a smoke cloud than systematic rings. 
But from our mouths as we talk we must produce numberless 
rings. 
One way in which rings are produced in perhaps as great 
numbers as from our mouths is by drops falling into the sea. 
If we colour the surface of a glass vessel full of water, and then 
let drops fall into it, rings are produced, which descend some- 
times as much as two or three feet. 
But the most striking rings are those produced in water, in a 
manner similar to that in which the smoke rings are produced, 
using coloured water instead of smoky air. 
These rings are much more definite than smoke rings, and 
although they cannot move with higher velocities, since that of 
the smoke ring is unlimited, the speed at which they move is 
much more surprising. 
In the air we are accustomed to see objects in rapid motion, 
and so far as our own notions are concerned, we are unaware of 
any resistance; but it is quite otherwise in water. Every 
swimmer knows what resistance water offers to his motions, so 
that when we see these rings flash through the water we cannot 
but be surprised. Yet a still more striking spectacle may be 
shown, if, instead of coloured water, a few bubbles of air be in- 
jected into the box from which the puff is sent ; a beautiful 
ring of air is seen to shoot along through the water, showing, 
like the lines of air behind the oblique vane, little or no ten- 
dency to rise to the surface. 
Such is the ease with which these vortex rings in water move, 
and so slight is the disturbance which they cause in the water 
behind them, as to lead to the conclusion that they experience 
no resistance whatever, except perhaps a little caused by slight 
irregularities in their construction. Their velocity gradually 
diminishes ; but this would appear to be accounted for by their 
growth in size, for they are thus continually taking up fresh 
water into their constitution, with which they have to share 
their velocity. Careful experiments have confirmed this view. 
It is found that the force of the blow they will strike is nearly 
independent of the distance of the object struck from the 
orifice. 
The discovery of the ring behind the disc afforded the oppor- 
tunity of observing the characteristics of these rings much 
better than was afforded by the smoke rings ; and also suggested 
facts which had previously been overlooked. The manner of 
NEW SERIES, VOL. I. — NO. III. U 
