192 



NATURE 



[October 17, 1912 



BRITISH RAINFALL IN 191 1. 



THE Director of the British Rainfall Organisa- 

 tion is to be congratulated on the volume 

 he has produced ^ dealing with the rainfall of the 

 British Isles, and for the compilation of which 

 he has the assistance of 5300 observers. As 

 time goes on the value of the work undertaken 

 is greatly enhanced, not only by the extension of 

 the observations and the greater accuracy of the 

 results, but also by the completeness of the dis- 

 cussions rendered possible by the accumulation 

 of data. The thoroughness with which the work 

 is carried out both by the voluntary observers and 

 by Dr. Mill and his assistants merits the greatest 



admiration, and is a masterpiece as a private 

 undertaking. 



A discussion of the distribution of rainfall in 

 time is given which will prove of very great value, 

 and is a matter of considerable interest even to' 

 the general public endowed merely with average 

 scientific craving. 



In a former volume for 1902, a first attempt 

 was made in the same direction, dealing only 

 with the observations for ten years, and these 



1 "Brilish Rainfall, 191 1." On the Distribution of Rain in Space and 

 Time over llie British Isles during the Year 1911, as recorded by more than 

 5000 Observers in (ireat Britain and Ireland, and discussed with Articles 

 upon various br.ancbes of Rainfall Work. By Dr. H. R. Mill. The Fifty- 

 first Annual Volume. Pp. 108+388. (London: Edward Stanford, Ltd., 1912.) 



NO. 2242, VOL. 90] 



embracing chiefly a dry period. Now a period of 

 twenty years, 1893 to 191 1, is dealt with, and 

 the results at 100 stations of established 

 accuracy have been collated, which may with 

 some confidence be expected to furnish a trust- 

 worthy average. 



There is naturally a relation existing between 

 the frequency and amount of rainfall, the wetter 

 western districts showing a greater frequency than 

 the relatively drier Eastern districts. 



The rain days for the year on the average cf 

 twenty vears range from 250 in the north-west 

 of Scotland and the west of Ireland to 150 in the 

 estuary of the Thames; and England, with the ex- 

 ception of the north-western and western districts, 

 has fewer than 200 rain days in the year. 

 The map of frequency, like that of 

 quantity, suggests very clearly the con- 

 trolling influence of the westerly winds 

 which predominate, and which are laden 

 with moisture from off the .'\tlantic on 

 their arrival over the British Isles. 



The abnormal year of 191 1 was be- 

 lieved to have been unparalleled for its 

 dry periods, and under the heading of 

 "Droughts in 191 1" a comparison is 

 made between the results for 191 1 and 

 the records of the last twenty-four years, 

 selecting one hundred well-distributed 

 stations" in the British Isles; this shows 

 that the surmise about 191 1 is not with- 

 out foundation. 191 1 had more absolute 

 droughts than any other year except 

 1 88-^ and it had the largest number of 

 partial droughts. An absolute drought 

 is no rain for more than fourteen con- 

 secutive days, and a partial drought a 

 period of more than twenty-eight con- 

 secutive days with a mean rainfall not 

 exceeding o'oi in. per day. The absolute 

 droughts in ig'i i were more than double 

 the average, and partial droughts little 

 short of three times the average. 



Dealing with heavy rains in short 

 periods, an exceedingly interesting table 

 is given showing the rainfalls of very 

 rare intensity lasting for one hour or less. 

 The heaviest authenticated measurement 

 is o',^3 in. in two minutes, which is equal 

 to the hourly rate of 9-90 in. at Chep- 

 stow in March, 1888, and this is followed 

 by o'50 in. in four minutes, which is 

 equivalent to 750 in. per hour, at Ilkley 

 in June, 1906. A reported fall of i'25 in. 

 in five minutes at Preston in August, 1893, which 

 gives a rate of 15 in. per hour, is accepted 

 with caution. At Beddington, in May, 1903, 

 a fall of 3'50 in. occurred in an hour. This table 

 is of considerable value, as it affords means of 

 comparison for such extraordinary rains as have 

 recently occurred in Norfolk, where at Norwich, 

 between noon and i p.m., September 26, the rain- 

 fall amounted to I'l.s in., and to 7*32 in. in 

 twenty-four hours ending 4 a.m., September 27. 



C. H. 



