1 897-] "Weather." . 51 



area storms. By a cyclonic storm is not necessarily meant a 

 cyclone or a hurricane, but simply a storm characterized by an 

 atmospheric pressure below the average, and having a wind 

 system blowing spirally inward, as do the winds of a genuine 

 cyclone. The fluctuations of the atmospheric pressure as indi- 

 cated by the barometer amount to about four inches. The 

 position of these areas of high and low barometer, especially 

 the latter, is the chief factor in weather forecasts. 



The circulating air-currents at the surface of the earth move 

 contrary to the hands of a watch. From this cyclonic action 

 the phenomenon so often observed of the wind blowing in an 

 opposite direction before and after the passing of a storm be- 

 comes obvious. In the area of low barometer we have an ascend- 

 ing current of warm air around which gyrates the anti-cyclone 

 of cold air with an inflow at the earth's surface. Although far 

 the greater part of the action of all and the whole of some storms 

 takes place 'within a mile of the surface of the earth, yet the 

 movement of upper clouds and occasional attendant peculiar 

 phenomena indicate quite clearly that the origin and most im- 

 portant phases of atmospheric changes must be assigned to the 

 upper strata of the air. The formation of depression or low area 

 is probably due to precipitation or formation of cloud, or is at 

 least very closely related in some way to the condensation of 

 aqueous vapour. The motion of the low area probably depends 

 on the prevailing direction of motion in the great body of upper 

 air in the vicinity of the low area. 



By plotting the isobars of mean annual pressure over the 

 northern hemisphere two areas of low barometer are found, one 

 over Iceland and the other over Bering Sea. The one over Ice- 

 land is the one towards which our Canadian barometric gradients 

 flow. An area of low barometer may be looked upon as a vast 

 caldron towards which and into which the atmosphere is flowing. 

 From this analogy we can see in a measure how the atmos- 

 pheric currents flowing over Canada toward the sink hole, so to 



