46 BOARD OF AGRICULTURE. [Pub. Doc. 



tion toward the east in the revolution of the earth, toward 

 the axis of the earth which has no motion, they are carried 

 ahead and come to us in the northern hemisphere as west- 

 south-westerly wdnds, and in the southern hemisphere from 

 the west-north-west. In these general air currents local 

 eddies or waves of higher and lower barometric pressure, 

 called respectively anticyclones and cyclones, are formed 

 and move along with the general current, influencing the 

 winds locally. 



If the local disturbance be a cyclone, the air at the centre 

 has become warmed, and, expanding, has been forced up by 

 the denser air from all sides, which, expanding in turn and 

 flowing up, gives place to other air, till there is a general 

 inflow from all sides ; not blowing directly toward the com- 

 mon centre, but, because of the revolution of the earth, 

 moving spirally around the centre in a direction opposite to 

 the movement of the hands of a watch in this hemisphere 

 and with the hands in the southern hemisphere. This area 

 will move along at the rate of one hundred to five hundred or 

 more miles in twenty-four hours, giving altogether diflerent 

 winds and weather in diflerent parts of its area, which may 

 cover a section several hundred miles in diameter. 



The approach of one of these storm areas is often noted 

 first by a veil of very high and fine clouds, which cause sun 

 and moon halos, the clouds thicken and appear lower, and 

 the wind, which at first was very light and from the east, 

 begins to increase perceptibly in velocity. The clouds soon 

 obscure the sun or moon, and the rain or snow falls. If the 

 centre of the disturl)ance passes to the north of us, the 

 winds veer to the south-east, then to the south, south-west 

 and to west and north-west as the centre passes, with the 

 breaking up of the clouds and with scjually conditions. If 

 the centre moves to the south of the place of observation, 

 the wind backs to the north-east, north and north-west, and 

 if it be in winter, snow usually falls. Behind the storm area 

 will come the anticyclone or wave of higher pressure, with 

 the wind blowing; out from the centre. These latter areas 

 are due to the descending current of air, which has flowed 

 up at the centre of some cyclone, and comes down to the 

 earth again in the anticyclone area, but dry and clean, 



