30 Professor Cleveland Abbe, M.A. 



the rotation of the water, not to its flow through the hole. Just so,. 

 a storm whirl occurs beneath a cloudy region where the buoyant clouds 

 are ascending, and the colder air is flowing inwards, around and upwards.. 

 Within such a whirl the barometer measures the local pressure of the 

 elastic gas and not simply the weight of the air above it. 



The rectilinear and the vortex motions, or the direct, the sinuous and 

 the spiral motions of fluids, offer most important but difficult problems 

 to the meteorologist and mathematician. When the air is moving very 

 slowly it can easily keep on in straight lines or very gentle curves, but 

 so mobile is it that when moving rapidly, nothing can prevent its 

 twisting into innumerable vortices, as shewn in the clouds and the 

 dust whirls. 



But I was speaking of Mr. Howard, and his storm of last July. I 

 find that the flow of dry air from the continent into this storm area has 

 deflected the whirl away from the dry area just as it does everywhere 

 in the northern hemisphere. Thus on the east coasts of North America 

 and of Asia the whirls are pushed from the dry land towards the south 

 and east ; on the west coast of Europe they are pushed from the dry 

 land towards the north and west, that is to say, these are the deflec- 

 tions from the normal or average. It is equally proper to say that the 

 storm centre advances or grows towards the region where the maximum 

 rain and snow occurs, i.e., towards the supply of rising moist air. 

 Apparently the north-west wind along your west coast was overlaid last 

 July by a drv north-east, and the latter had little moisture wherewith 

 to feed this whirl of last July, so it deflects to the south, passed east of 

 Agulhas, and then moved north-eastward. 



But you need stations fuither north, and possibly I have not fully 

 appreciated all the forces at work in this storm, so that Mr. Howard 

 may yet prove to have the more correct view. All that I would insist on 

 to-night is, that storms and weather can be satisfactorily predicted 

 twenty -four hours in advance by the proper use of the telegraph, that 

 such predictions or even vaguer ones are far better than to have none 

 at all, and that through Mr. Howard's knowledge you can in South 

 Africa have as good a weather service as you are willing to pay 

 for. 



Cleveland Abbe. 



