360 



SCIENCE PROGRESS 



variations of pressure which are characteristic of a line-squall 

 and are shown on the maps arranged in lines athwart the 

 isobars marking the position of the squall. Eig. 10 shows 

 the phenomena recorded at Kew Observatory during the 

 passage of the squall. It enables us to note the characteristic 

 events which identify a line-squall : slight rise of pressure, 

 marked fall of temperature, sudden veer of wind (generally a 

 violent gust at the onset) and a sudden shower of rain. 



Fig. 12 



KEW OBSERVATORY 

 Pressure - sudden rise of CB inch 



to MOON 2 



*"| l/l*! 1 O 



Uil 111 MJ J<» 



■»' mi 



Ml 313 M>*1 



Temperature f Dry and Wet Bulb) 

 The figures iAc- the readings 

 At fi'Cd hours 



Fig. io. 



shows the isochronous lines for successive hours which mark 

 the advance of the squall with a linear front across the map 

 from north-west to south-east. 



These examples of line-squalls are very conspicuous cases 

 of phenomena of quite frequent occurrence in south-westerly, 

 westerly and north-westerly weather. The gentlest example 

 that I know is the narrow band of high cloud at Aberdeen, 

 represented in fig. n, which was accompanied by an appro- 

 priate change of wind ; the severest example was in the storm 



