1915-16.] The Dynamics of Cyclones and Anticyclones. 183 
It is not that they cannot be bent — as a vortex ring is in many respects 
simply a cyclone with its two ends joined, — but that bending puts a consider- 
able strain on the structure, and gives it its elasticity, which causes it to 
vibrate when distorted. The low pressure in the centre of the circling air 
which forms the ring keeps the ring from expanding or straightening out ; 
but if a small piece be cut out of the ring, the low pressure inside is 
weakened by the entrance of air, and the ring begins to straighten out and 
is rapidly dissipated. 
These small cyclones do not help us much towards understanding the 
movements taking place in cyclones in our atmosphere. The conditions are 
all very different. The height of these small cyclones is many times their 
diameter, while in the atmosphere the height may not be 1/200 of the 
diameter. It is evident, therefore, that the air passing through a cyclone 
in the atmosphere will only undergo a proportionately small amount of 
rotational movement. 
Note added February 23, 1916. 
There is an interesting difference in the appearance of a water jet 
escaping from still water and one escaping with circular motion, which 
appears to be worth recording here. Let us use a circular metal 
vessel 30 cm. in diameter and 8 cm. deep, with a hole in the centre 
1 or 2 cm. in diameter which can be closed from below. This 
vessel is filled, and a circular motion given to the water. Some 
time should be allowed for the water to get into a uniform circulation. 
When the circulation is sufficiently slow the outlet in the bottom is 
opened. When this is done the well-known jet at first appears like 
a solid tapering rod. But soon the outflowing water develops a cyclone 
strong enough to give rise to an air space in the centre. This air space 
develops downwards and passes through the outlet, the vena contracta 
disappears, and a series of hollow globes of water is formed, the uppermost 
one being more than twice the diameter of the outlet. See fig. 3, where 
AA is the bottom of the vessel containing the water, B is the first bulb 
which develops immediately below the outlet, while below it another 
globe, C, appears, somewhat longer and narrower than the top one. Below 
the second bulb there sometimes appears another, or others, gradually 
decreasing in diameter and increasing in length. The dotted lines in the 
figure show the air space extending down from the whirling water in A A 
through the bulbs. As the shape of the bulbs depends greatly on the rate 
of rotation, the upper bulb is often not so spherical as shown, but may be 
more like the second bulb, C. 
