64 Transactions. — Miscellaneous. 



manner observed in the anti-cyclones and cyclones, no 

 thoroughly exhaustive theory has yet been established to 

 account for them. Yet these two systems are practically in- 

 variable in each hemisphere, and in I'everse directions in the 

 two hemispheres. It is clear, therefore, that they depend on 

 fixed laws, however complicated those laws may be owing to 

 the extreme variability of the behaviour of the atmosphere 

 under different conditions of pressure, of temperature, and of 

 moisture ; and, also, it is evident that the rotation of the 

 earth rules the directions of their rotation. 



In a popular way we may perhaps regard the phenomena 

 of the anti-cyclones in this way. 



The total mass of air between the equatorial belt and the 

 calm belt near 30° latitude is about equal to the total mass of 

 air betw^een that belt and the pole, hence the opposing cur- 

 rents must meet in that zone. As they form the upper strata 

 of the atmosphere, with very little pressure from superincum- 

 bent air, that current which is in any degree lighter than the 

 other rises and rides over it, compressing and forcing down the 

 other ; and this process of one stratum gliding over another is 

 being constantly renewed by fresh air pressing on behind from 

 the opposite sides. But this sandwiching of opposing currents 

 and their piling up above one another must reduce their 

 onward velocity and increase their tendency to deflect to the 

 left, while at the same time they are being pressed down- 

 wards ; it follows that, as the fronts of these successive layers 

 of air, after passing over or under the front edges of the oppos- 

 ing layers, are turned to the left and downwards, a downward 

 screw -like circulation to the left (or against the hands of a 

 clock) is set up and maintained. The level at which the out- 

 flow of air takes place, and the principal direction of that 

 outflow, depend on the pressures in the vicinity, the princi- 

 pal outflow being towards the centre of lowest pressure. 

 Thus in some measure cyclones are supplementary to anti- 

 cyclones, forming, as it were, drainage-basins for their out- 

 going air. Yet there is no permanent connection between the 

 two circulations. Eather, apparently, does the cyclone attack 

 the anti-cyclone, which offers a more or less passive resistance 

 to its onward movement. 



The Hon. Ealph Abercromby distinguishes two classes of 

 cyclones which reach England — those born at the edge of the 

 anti-cyclone tropical belt and moving north-east, and those 

 born in the arctic regions and moving south-east. Ours seem 

 to correspond with the latter. 



The theory of the cyclonic circulation — of the birth and of 

 the progress of cyclones such as we experience in these lati- 

 tudes — is still in its infancy. Yet, as the direction of the 

 circulation is invariable (with the hands of a watch in this 



