Nov. 4, i8S6] 



NA TURE 



^5 



and thereafter descends to the low-lying grounds of the 

 valleys, displacing the warmer air below. During the 

 unusually dry clear months of January and July iS3l the 

 mean temperature of Park Hill exceeded that of Bed- 

 dington by y^ and s'', respectively. Hence the first three 

 of the five stations which are on sloping ground have, 

 though at greater elevations than the other two stations 

 below, higher mean temperatures. 



This peculiarity in the distribution of the night and 

 the winter temperature becomes the more intensified as 

 the \alley is deeper and its sides steeper, and as calms 

 and light winds prevail. Thus at Klagenfurt, situated in 

 one of the valleys of the Tyrol, the mean temperature of 

 Januar)- is 2o'7, whereas at the station of Obergipfel, 

 about seven miles distant and 4270 feet higher, the mean 

 for the same month is 19' 9, being thus less than a degree 

 lower than that of Klagenfurt. The subject is one that 

 has seldom received the earnest attention it deserve?, 

 particularly in drawing the isothermals of the globe. The 

 Croydon Club would make a clear addition to their 

 observing-system if new stations were established on 

 knolls in the valley of the Wandle for the further prose- 

 cution of this inquiry. 



The means of temperature from Greenwich and Kew 

 would have had real value in this inquiry if Mr. Eaton 

 could have availed himself of observations made at these 

 Observatories with thermometers exposed in the Steven- 

 son screen. But, as pointed out, the different modes of 

 exposing the thermometers render the results of the three 

 systems of observing incomparable inter sc. Thus the 

 mean of the daily highest temperature of August for the 

 five years is 72''5 for Greenwich, and d'f'i for Kew. 



The rainfall has been far more extensively observed in 

 the district, the returns of no fewer than seventy stations 

 being available. Grouping the stations according to 

 height, the annual amounts at stations below 200 feet 

 show a mean of 2327 inches ; 200 to 400 feet, 25'39 

 inches; 400 to 600 feet, 29' 12 inches; 600 to 800 feet, 

 3r66 inches; and above 800 feet, 3r36 inches. The 

 largest amounts of rain occur not on the ridge of the 

 North Downs, but some distance on the lee-side in re- 

 gard to the prevalent rainy south-westerly winds ; and the 

 amount at like elevations seems also to diminish from 

 west to east. As regards the monthly rainfall, the depth 

 is greater in the upper groups ; but the ratios of the 

 monthly to the annual fall show that in spring, but more 

 particularly in summer, there falls proportionally a larger 

 amount of rain in the lower group of stations, whose 

 average elevation is 193 feet. The relatively large in- 

 crease in the summer rainfall over low-lying plains is one 

 of the most striking facts in the geographical distribution 

 of the rainfall, and is probably due to the physical causes 

 concerned in the development of thunderstorms. 



NOTES ON THE RECENT SIVAR.UING OF 

 APHIDES 

 'T'HE immediate cause of the sudden appearance of 

 -'■ clouds of insects in certain localities is not very 

 apparent, but it may be surmised that the predominance 

 or scarceness of their natural insect foes has much con- 

 trol over the phenomenon ; added to which must be taken 

 into account the eflects of weather and temperature. A 

 few days ago I had a notice from an obliging Birming- 

 ham correspondent, Mr. George Baker, who kindly fur- 

 nished me with the following particulars : — 



On October 5 the town of Mansfield, on the borders of 

 Sherwood Forest, was visited by a cloud of Aphides, 

 which swarmed in the town and over the country round, 

 across an area of many miles. The town was visited 

 " literally by millions ; every one, as they walked along, 

 waving their handkerchiefs or newspapers before their 

 faces to avoid inhaling the insects. . . . Wet paint was 

 covered by a mass of these black Aphides." This swarm 



continued with decreasing numbers throughout five days, 

 and heavy rain during part of this time did not seem 

 much to affect them. On the road to Nottingham these 

 insects were noticed as engaged in singular gyrations and 

 undulatory dances above the tops of the spruce-firs, there 

 forming dense pyramidal columns. 



A similar cloud, but less remarkable as to numbers, was 

 observed about the same time at Birmingham ; which, 

 however, as the town must be at least 50 miles distant, 

 can be scarcely considered as forming a part of this same 

 swarm. Possibly similar causes operated to produce the 

 like phenonenon in both places. 



These insects proved on examination to be Rhopalo- 

 siplium dianlJii of Schrank, which is identical with 

 Aphis pcrsiai; of Morren, and A. I'apce of Curtis, and 

 A. vastator of .Smee. It is a veritable pest in some years, 

 doing considerable damage to turnip, mangel, and other 

 crops, and in our gardens injuring our peach-trees. This 

 present notice of its- swarming is, however, by no means 

 unprecedented. 



In September and October 1834 Morren noted an im- 

 mense swarm all over Belgium, and states his belief that 

 it came across the sea from England. He says they ob- 

 scured the light of day, and covered the walls of the 

 houses so as partially to conceal them. Gilbert White 

 notes that in August 1785 the people of Selborne were 

 surprised by a swarm of " smother flies." Those that 

 were walking in the street found themselves covered with 

 these insects, which blackened the hedges and vegetables 

 round. White thought these might be emigrations from 

 the hop- gardens of Kent and Sussex, and from those near 

 Farnham. If so, the species differs from the insects 

 above noticed. 



The choice of high objects to dance over is not con- 

 fined to Aphides, e.g. many of the Tipulidre. The singular 

 persistent dance of Anlkomyiii mctcorica over the heads 

 of horses is familiar to all. G. B. Buckton 



NOTES 

 A MOST attractive group of birds has just been placed by 

 Prof. Flower in the great hall of the Natural History Museum 

 at South Kensington. The case is intended to illustrate the 

 hybridisation of species in a state of nature, and the species 

 selected are the hooded and carrion crows {Corvus comix and 

 C. corone) and the European and Asiatic goldfinches ( CarJiu-lis 

 elegans and C. orientalis). The series of these birds has been 

 presented to the Museum by Mr. Henry Seebohm, who procured 

 the specimens himself during his travels in Siberin. The caseof 

 the crows is one of the few instances known of actual wild 

 hybridisation, though many more are suspected, especially 

 among the game birds. It is certain, however, that wherever the 

 colonies of hooded crows meet the carrion crow throughout the 

 Palrearctic region the two species interbreed freely, and the 

 result is shown in the young, the gray saddle-back of the hooded 

 crow exhibiting a considerable admixture of black owing to the 

 strain of C. corone in the parentage. The case of the goldfinches 

 is not quite so completely proved, but is apparently a parallel 

 instance of hybridisation. The British Museum has been for 

 some time indebted to Mr. Seebohm forveiy valuable presents 

 of birds, which have been mounted in the bird-galleries. Not 

 long ago he gave a specimen of Ross's gull [Rhodiislctiiia rossi), 

 one of the rarest of the Larida, and a species which was a 

 desideratum to the national collection. He presented also, last 

 year, a fine case of Steller's sea-eagle {Haliactus pela^iciis) from 

 Kamchatka. 



The Geodetic Conference began its meetings in Berlin last 

 week. The countries represented are Belgium, by two dele- 

 gates ; Denmark, by one ; Germany, by fourteen, including 

 Prof. Dr. Fbrster, of the Royal Observatory, Prof. Helmholtz, 



