'50 



NA TURE 



[December 17, 1891 



its vertical scale is at the right). It will be understood that each 

 year-point of those curves represents an average of five years. 



It would appear that easterly winds (north-east, east, and 

 south-east) at Greenwich have been increasing in prevalence, on 

 the whole, since about 1865 ;. the five years' average for that 

 year is 83 "8, and this grows to 111-4 in '886 (about one-third). 

 On the other hand, westerly winds (north-west, west, and south- 

 west) have diminished, on the whole, since 1861 ; the five years' 

 average for that year is 2iO"8, and this diminishes to I59'0 in 

 1887 (about one-fourth). 



Judging by the past, we might perhaps consider that we must 

 be near a decided turn of the curves ; possibly past it in the case 

 of easterly winds ; in which case we should look for more westerly 

 and less easterly wind in the near future. 



A. B. M 



(a) = Nonh-eas', eas', and ; 



jth-east wind (Greenwich), (b) 

 Actual figures smooth id by inea 



North-west, west, and south-west wind (Greenwich), 

 s of five-yea averages. 



From the "crest "of (a) in 1857 to the last point is thirty 

 years. Are those long variations possibly a manifestation cf 

 the thirty-five years' period of Brueckner? 



These curves might have begun at an earlier date, for the 

 figures commence in 1841. But in the earlier years, and ap- 

 parently to about 1855, a larger proportion of days seem to have 

 been reckoned as "calms'' than afterwards (owing to a differ- 

 ence of rule), so that the curves to about 1855 are not exactly 

 comparable with the remaining portions. 



I append a few figures, showing the derivation of maximum 

 and minimum (or low point) averages : — 



14 .. 

 NO. 



1^55. 



(a) 1857 max. 



1357 18s"? 



. 113 ... 126 



VOL. A5] 



1859 Aver.^ge. 



99 1 12-6 



The Migration of the Lemming. 



My attention having recently been drawn to the question of 

 the migration of that little Norwegian rodent the lemming, as 

 a serious obstacle to the theory of natural selection, and hence 

 to evolution generally, I write to call attention to what appears 

 to me to be a possible factor in the starling of the migration. 



It is that when th^ lemmings become too numerous for the 

 means of subsistence upon the inland plateaux, which may be 

 described as their home, the "fittest" lemmings, by battle, 

 turn out from the district all those of their weaker brethren who 

 are unable to withstand the contest. 



The unfittest being thus driven out from their home, are 

 forced to migrate somewhere. Why they move incessantly to 

 the westward seems a problem yet to be satisfactorily solved. 



