DYNAMICS OF CYCLONES AND ANTICYCLONES. 137 



outer air for the same amount of ascent, as roughly indicated in fig. 3. This in- 

 draught of the lower air into the core of the cyclone is one of great importance in 

 connection with meteorological phenomena, and will be referred to later on. The 

 reason for the lower air being drawn into the core is very 

 obvious. The air near the ground, or surface of the table 

 ■in this case, has less tangential movement than the air higher < 



up, owing to its motion being retarded by friction. The ,.-- — ^ 

 result of this is that whilst the greater centrifugal force of \ „ 



the upper air keeps it back against the low pressure in the 



cyclone, the lower air as it moves nearly radially offers but 



little resistance to the in-draught. Hence the lowest stratum of air being at the lower 



end of the cyclonic tube, it is drawn into the very centre. 



Anyone can make similar experiments to these without a special draught tube, and 

 study for themselves the conditions necessary for the formation of cyclonic circulation. 

 All that is necessary is a good fire, with a free-going chimney, and a wet cloth. The 

 cloth is hung up in front of the fire and pretty near it, so as to cause a liberal amount 

 of condensed steam to rise from its surface. Probably without some arrangement of 

 the draughts in the room no cyclone will be formed, and the vapour will rise vertically, 

 keeping close to the wet cloth. But if the room has a door or a window in the wall 

 at right angles to the fireplace, and at the side nearest the fireplace, so as to cause 

 the air coming from it to make a cross current past the fire, then a cyclone will be 

 formed and the steam on the wet cloth will be seen circling round, and when the 

 cyclone is well formed, all the steam is collected into the centre of the cyclone and 

 forms a white pillar extending from the cloth to the chimney. If the cross-draught 

 be equally strong at top and bottom of the wet cloth, it will be necessary to screen 

 the current from either the top or bottom of the cyclonic area. Should there be no 

 suitable draught in the room, then an artificial one may be made in any direction 

 -across one side of the wet area. 



We have seen from these experiments that no cyclone can form without some 

 tangential movement in the air entering the area of low pressure. The next question 

 one naturally asks is — Has this tangential motion any other effect on the cyclone? 

 From the fact that some of the air entering the cyclone has motion in a particular 

 direction, we would naturally expect that unless an equal amount of air, moving in 

 the opposite direction, also entered at the same time on the other side, that the whole 

 system would move in the direction of the greatest tangential force. If we examine 

 the cyclone produced in our artificial conditions with the draught tube we shall find 

 that this is the case. The lower end of the cyclone bends away from under the 

 centre of the apparatus, moving in the direction of the tangential current. 



This point can, however, be better illustrated by means of water vortexes. Using 

 the circular vessel as before, and in order to make the tangential current on one side 

 stronger than on the other, all that is necessary is either to put the outlet for the 



