138 MR JOHN AITKEN ON 



water excentric to the walls of the vessel, or more easily by taking a strip of thin 

 metal, having a breadth the same as the depth of the vessel and of a length of a little 

 more than the diameter, and bend it into its place in the circular vessel, as shown in 



fig. 4. When the water now runs out it all passes round the 



vessel, and as the passage between the outlet, that is the 



centre of the cyclone, and the temporary division is narrower 



than at any other place, the water has to pass this part at a 



much greater velocity than at any other place, and the result 



is, the top of the vortex no longer remains over the outlet, 



but travels in the direction of the quickest moving water, 



showing that, as might be expected, the quickest moving 



water tends to carry the centre of the vortex along with it< 



See fig. 4, where the small dotted circle represents the outlet 



FlG _ 4> and the full circle the top of the vortex, which is carried by 



the water to the right, the direction of movement of the 



water being shown by the arrows. In addition to moving in the direction of the 



strongest current, the centre seems also to be attracted towards the quickly-moving 



area, but to this point I shall not further refer at present. 



Turning now from these experimental observations, let us see how far they help us 

 to understand the phenomena in cylones and anticyclones in our atmosphere. At the 

 outset I may say that in forecasting attention seems to have been given too exclusively 

 to what takes place in cyclonic areas, and too little to the part played by anti- 

 cyclones. We have been looking too much on the cyclone as the active member of 

 this dual partnership. But I think we will have to admit that the anticyclone is not 

 the sleeping partner it is generally supposed to be, whose only duty is to follow and fill 

 up the depressions made by the active partner. A closer examination of the part played 

 by the anticyclone will show that it also is an active though silent partner in the firm, 

 and that it initiates and keeps up its own circulation, and collects and forwards the 

 material with which the more showy partner, the cyclone, makes its display. The 

 anticyclone also in a great measure directs the path of the cyclone and adds much 

 to its cyclonic motion. In fact the vertical circulation seems to be kept up by the 

 partners in this dual system playing into each other's hands, and neither could work 

 efficiently without the other. 



Let us now look at what the effect would be if there were no cyclones or anti- 

 cyclones in our atmosphere. Suppose a large area, say, some hundreds of miles in 

 diameter, on the earth's surface over which the air was still, suppose further that the 

 sky was cloudless and a summer's sun was shining. After a time the conditions 

 would become unstable and columns of air would begin to ascend at many points all 

 over the area wherever the air happened to be most highly heated and charged with 

 vapour. The result of this would be a disorderly mob of ascending currents without 

 leader, organization, or combined effort. These small isolated attempts at vertical 



