THE BIRTH, LIFE, AND DEATH OF A STORM. 689 



whether or not the time-honored rules for handling ships in rotating 

 storms require modification. 



I shall now leave the subject of the air-motion, and proceed to de- 

 scribe the phenomena of a cyclonic disturbance when it passes over us. 

 In the first place, very few of them, in these latitudes, exhibit much 

 approach to a circular shape, as regards the course of the inner isobars, 

 and we may say that none of them develop equal violence in all seg- 

 ments. The reason of these differences in the force of the wind is to 

 be found in the distribution of pressure in the vicinity of the storm 

 area, for if on any side of that area there exists a region of high barom- 

 eter readings, on that side steep gradients will be produced, and of 

 course proportionably great violence of the wind. The actual weather 

 phenomena of a typical cyclonic disturbance, if plotted on a diagram, 

 show very clearly how cloud and rain prevail over the whole front of 

 the system, and how in the rear, where the wind is northwesterly, the 

 sky clears up. There is one fact worth remembering about these 

 storms, and that is, that just before the sky clears a very smart squall 

 of rain frequently comes on ; so that we get this practical hint : if, 

 during a westerly gale, we find the rain becoming exceptionally heavy, 

 we may look for the weather speedily to clear up. 



Such a diagram also shows us that it is quite a mistake to consider 

 all east winds as dry ones, for in a cyclonic system the cloud area 

 extends on the northern side, where the wind is easterly, nearly as 

 much as on the southern, where the wind is from the westward. In 

 fact, many of our wettest days occur with easterly winds, when one of 

 these depressions passes to the south of the station where we may be. 



I shall now proceed to give a slight sketch of what we have learned 

 of the movement of storms. This, as far as we can see, is regulated 

 by the position of the areas of high pressure, or, as they are called, the 

 anticyclones. This is a term introduced about fifteen years ago by 

 Mr. Francis Galton, to indicate an area of excess of pressure out from 

 which the air is slowly whirling with a motion opposite to that which 

 it has in cyclones. If we find an anticyclonic area existing over any 

 region, we know that the cyclonic disturbances will skirt round it and 

 develop their strongest wind on the side which lies closest to the dis- 

 trict of high pressure. 



Thus if the anticyclone lies over France, the cyclonic disturbances 

 will move from west to east over the British Isles. If the area of high 

 pressure lies over England, the depressions will sweep outside the 

 Scotch coast, and reach Norway noi'th of the sixtieth parallel. If the 

 anticyclone lies to the westward, and the pressure is higher in Ireland 

 than in Great Britain, there is danger of northerly gales on the east 

 coast of England, from cyclonic disturbances traveling southward 

 over the North Sea. 



In every case the cyclone moves with the prevailing wind along its 

 track. 



vol. xv. 44 



