74 



are close to or further apart from each other. "Where the 

 isobars crowd together the violence of the storm is greatest, and 

 where they are far apart the ^ands are light or moderate." In a 

 general way, it may be stated that " the occurrence of a storm of 

 wind is determined by the simultaneous occurrence of great 

 differences of pressure between places not far distant from each 

 other." Mr. Scott remarks that " no storm of any serious extent 

 is ever felt over the United Kingdom unless there be an absolute 

 difference in barometrical readings exceeding half-an-inch of 

 mercury between two of om- stations."* 



In all cases of cyclonic disturbances, at least in the northern 

 hemisphere (for in the southern hemisphere the law is reversed), 

 the wind sweeps round the central area of depression against 

 icafch hands. This is just the contrary to what is the case in 

 anti-cyclones, or areas of high pressiu'e characterised by more settled 

 weather, in which the isobars are much further apart, besides other 

 marked differences that present themselves. Of anti-cyclones, 

 however, we are not called upon to speak just now. To an 

 observer at a fixed station the -wind in a cyclone ■noil be different, 

 according to how he is situated with reference to the centre, and 

 anywhere the ■wind will change from time to time as the storm 

 advances. Sometimes these changes are very sudden. Scott has 

 remarked that " one of the most striking characteristics of a 

 cyclonic storm is a sudden shift of wind which takes place between 

 S.W. and N.W., accompanied frequently by a heavy squall and a 

 shower, together \n\h an almost instantaneous fall of temperature. "t 

 I have recorded elsewhere some remarkable cases of these squalls 

 noticed in Cambridgeshire;:!: the s])lashes of rain accompanying 



* "Weather Charts and Storm Warnings," p. 43, from which book, as also 

 from ''Buchan's Handy Book of Meteorology," much assistance has been 

 derived in this part of the subject. 



t ''Weather Charts," p. 60. 

 + " Observations in Meteorology," pp. 251—253. 



