190/.] 



Meteorology :al Statistk :s. 



7 



20 week 



f 60 



I 



39 

 42 



135 



I 20 

 I64 J l8 



12 

 IO 



12 



Rain Call. 







Zero. 





, , between 



0 *o 



and 



01 inch 



,11 51 



0 I 



» 1 



O '2 



J 5 



" " 



0'2 





°'3 



>> 









0*4 



' ' 







" 



u 5 



>) 









o*6 







o - 6 





07 



) > 





07 



il 



o-8 







o-8 



> > 



0-9 



J > 





0-9 





1 0 



) J 



> ) > > 



1 -o 





i"S 



J > 



1 1 ■>■> 







2"0 



J > 



The weekly rainfall was thus less than o-i in. on 80 out of 325 

 occasions, i.e., in about a quarter of the total number of occur- 

 rences. The median value is about 0-30 in., whereas the average 

 is found to be 0*38 in., or nearly o - 1 in. greater than the median. 

 If the limits for " moderate " suggested above were adopted, 

 half the values would, on the average, be classified as "light," 

 and over long periods weeks of " light " rainfall would be 

 always in excess. 



A further disadvantage in using a fixed divergence from the 

 average as a criterion is that a given divergence has a different 

 significance in different districts and at different seasons of the 

 year. For instance, in the South of England a week in which the 

 rainfall exceeded the average by 1 in. would be recognised by 

 universal consent as a very unusual occurrence, but in the North 

 of Scotland a week of similar excess would not be regarded in the 

 same light, even if regard be had to the greater average fall. 

 Similar considerations apply with almost equal force in the cases 

 of the remaining meteorological elements. 



The classification adopted in the Weekly Weather Report is 

 based on the frequency distribution of the values for the 25 years, 

 1881 to 1005. The definitions are expressed as probabilities as 

 follows : — 



Wantith. — The week's warmth is Called unusual if it is so much above the average 

 for the time of the year that, In the fong run, it is likely t<> occur, for that week, only 

 once ill three years, and it is marked :•< > y unusual if it is likely to occur, for that 

 Week, only once in twelve years ; similarly it is called defiicnt if it is «,<> much below 

 the average for the time of the year that it is only likely to occur, for that week, once 

 in three years, and very deficient if it is likely to occur, for that week, only once in 

 twelve years. Otherwise it is called moderate. 



Rainfall. — The week's rainfall is called heavy if it is so much above the average for 

 the time of year that, in the long run, it is likely to occur, for that week, only once in 

 tine- year-, audit is marked very heavy if it is likely to occur, for that week. Only 

 6nce in twelve years ; similarly it is called light if it is so much below 'he average for 



