DYNAMICS OF CYCLONES AND ANTICYCLONES. 145 



currents were taken from the observations made by Messrs Bolam & Kedpath at Leith, 

 along with those made by myself. The direction of the lower current is given by the 

 winds, whilst the direction of the upper current is shown by the cloud movement. The 

 result of this examination of the cyclones in the atmosphere shows this feature 

 in quite a distinct manner. In all cases in which there was any difference in the 

 recorded directions of the upper and lower currents, the lower current flowed more 

 directly towards the centre of the depression than the upper. It was also noticed 

 that the upper current was frequently almost quite tangential, apparently not 

 pointing at all to the centre of the depression. The observations used in investi- 

 gating this point were almost all taken on the side of the depression on which the 

 barometric gradient was steepest and winds strongest, and it would seem to indicate 

 that the inflow towards the centre on this side — particularly of the upper air — is 

 less than on the other sides. This result is indicated in the experimental part of the 

 paper, where it is shown that the air on the side of the cyclone which receives the 

 greatest tangential force curves inwards less than the air on the other sides. 



The upper currents moving more tangentially than the lower ones has the effect, 

 when a depression is passing any station, of making the upper currents appear to veer 

 in advance of the lower. For instance, with a depression to the north of the point of 

 observation, the wind will be south of west, whilst the cloud carry will be about west, 

 and when the depression has passed eastwards the wind will change to west, whilst the 

 carry will have some north in it. It may be as well to note here that it is possible 

 that the upper part of the cyclonic column may travel in advance of the lower, owing 

 to the friction on the earth's surface acting as a drag on the lower end. If this be 

 the case it will in part explain the veering of the upper currents in advance of the 

 lower. 



We shall now turn our attention to anticyclones, and see what part they play in 

 the vertical circulation of our atmosphere, as too little attention has, I think, been 

 given to them. The sun's heat seems always to have been looked upon as the great 

 source of the energy in our winds, to the exclusion of the effects of cold. It is as if, in 

 studying a steam-engine, we had devoted our attention to the boiler and furnace, and 

 neglected the condenser. The engine would no doubt work without the condenser, 

 though not so efficiently, but it may be doubted whether heat alone would work a 

 cyclone without the cold-driven anticyclone. Its absence, at least, would be a greater 

 loss to the vertical circulation than the loss of the condenser to the engine ; unless, 

 indeed, the engine was working at a very low pressure. 



It is well known that the mean pressure over continental areas is high during 

 winter and low during summer. That is just as the sun's rays during summer, by 

 heating the air over continental areas, gives rise to cyclonic conditions ; so the earth's 

 radiation during winter gives rise to anticyclonic conditions, and this cooling of the air 

 seems to be as true a cause of vertical circulation as the heating of it, though perhaps 

 not to the same extent. If this be the case, then we ought to give more attention to 



