028 



NATURE 



[July 14, 192 1 



Greenwich for the six months April to September 

 was 22-21 in., whilst for the following summer, 

 1904, it was 869 in. "British Rainfall," dealing 

 with observations from 1726 to 1891, shows that 

 during the first forty years the rainfall in only 

 nine years reached the average, and from 1738 

 to 1762, a period of twenty-five years, there is 

 only one year above the average; this is a more 

 persistent drought than has occurred in the nine- 

 teenth or twentieth century. There was a suc- 

 cession of wet years ending with 1882, and this 

 was followed by a very dry period. In the twenty 

 years 1883 to 1902 the Greenwich observations 

 show an aggregate deficiency of rain amounting 

 to more than 40 in. During this period there 

 were sixteen years with a deficiency, one year 



with the average fall, and three years with an 

 excess. Each year from 1895 to 1902 had a 

 deficient rainfall, the total deficiency in the eight 

 years amounting to 25-5 in. 



The question of interest is now : When will 

 the exceptional heat and drought of the present 

 year cease? The absence of rain is continuing 

 well into July, and each week the drought is 

 becoming more serious over the whole country. 

 The increased interest in meteorology, brought 

 about by the late war, has added much to the 

 staff and efficiency of the Meteorological Office. 

 Every effort is being made to improve our know- 

 ledge of the weather changes, and probably in a 

 few years it will become possible to predict the 

 chief characteristic features of a season. 



The Scarcity of Swallows. 



Bv Dr. Walter E. Collinge. 



FOR some years past certain ornithologists have 

 directed attention to the decreasing number 

 of swallows seen in the British Isles during the 

 months from April to September. This diminu- 

 tion was particularly marked in 1918 and 1919, 

 less so in 1920, but is still more apparent in the 

 present year. For a time the scarcity was denied 

 by many, or stated to be only of local occurrence, 

 but the condition of affairs during the present 

 season is sufficiently well marked to convince the 

 most sceptical. 



The swallow economically is one of our most 

 valuable birds, its food consisting practically en- 

 tirely of insects, and any scarcity of these birds 

 removes a most important factor in the destruction 

 of injurious insects. The causes which have led 

 to this scarcity are not at present all known, but 

 there are some which have been operating for a 

 considerable time past, and their effects are now 

 making themselves felt. 



First, there is the deplorable mortality of 

 migrants which takes place around our coasts in 

 connection with the lighthouses and lightships, 

 and, as has previously been pointed out, a con- 

 siderable percentage of these birds might be 

 saved. Something towards minimising this 

 danger has already been done, but the swallow is 



a day-migrant, and so largely, if not entirely, 

 escapes this danger. 



The enormous increase of the house-sparrow 

 during recent years has undoubtedly had much to 

 do with the decrease of the swallow. Not only do 

 the sparrows take up their abode in the swallows' 

 nests, but they molest and persecute the birds 

 during the whole period of incubation. In the 

 United States there has of recent years been a 

 very serious decrease in the number of house- 

 martins due to this cause. 



There are, however, other causes for the 

 present scarcity which do not arise in this 

 country. In 1918 and 1919 the continuous 

 waves of June migrants were unobserved or of 

 very short duration, and during the present season 

 they have been still fewer, all of which clearly 

 indicates a diminishing immigration. Moreover, 

 in 1919 and 1920 the majority of the swallows 

 commenced their southern migration early in 

 August. 



In view of the importance of the swallow 

 economically, the question is one calling for im- 

 mediate attention and investigation, and until we 

 know more about the matter it might be well to 

 place this bird and its eggs under stricter pro- 

 tection. 



The King George V. Dock, London. 



A FUNCTION of special interest and import- 

 ance in the history of the Port of London 

 was performed on Friday last, when the King 

 visited North Woolwich for the purpose of open- 

 ing and naming the new dock of the Port of 

 London Authority which has been under construc- 

 tion since 1912. 



The addition to the enclosed water area of the 

 port amounts to 64 acres, and as the depth of the 

 dock is 38 ft., the new accommodation will prove 

 extremely useful for large ocean-going vessels of 

 the present day. The dock is entered by a lock 



NO. 2698, VOL. 107] 



800 ft. long and 100 ft. wide, having a depth of 

 45 ft. over its sill at high water, and 20 ft. less 

 at low water. The capacity of the chamber can 

 be increased to a maximum length of 910 ft. by 

 placing a caisson in a special recess instead of 

 using the innermost pair of gates. The dock 

 averages 600 ft, in width, but tapers from east 

 to west. On the north side there is a concrete 

 quay wall of the ordinary type. On the south 

 side a somewhat novel arrangement has been 

 adopted. Projecting into the dock, and parallel 

 with the quay line at a distance of 54 ft. there- 



