566 Notices of Memoirs— F. W. Harmer — Winds and Climate. 



disappearance of the great ice-sheets, as may be the alternate 

 humidity and desiccation of the great basin of Nevada, the former 

 existence of the mammoth on the shores of the Polar Sea, etc. 



It is difficult, however, to restore hypothetically the meteorological 

 conditions of the Pleistocene epoch, on the theory that the maximum 

 glaciation of the eastern and western continents was contemporaneous. 

 At present the influence of the Gulf Stream, and the south-west 

 winds caused by the Icelandic cyclone, carries in winter a com- 

 paratively warm climate, and low pressures, northwards into the 

 Arctic Circle, but no permanent ice-sheet could have existed in 

 Great Britain under such circumstances. Cyclones and anticyclones 

 in regions more or less contiguous are, however, necessarily com- 

 plementary, in order that the vertical circulation of the atmosphere 

 may be maintained. The existence of an enormous polar anticyclone, 

 extending southwards over a great portion of Europe and North 

 America, would have involved also that of a cyclonic system of 

 corresponding importance in the North Atlantic, a region which 

 must have been at all seasons warmer than those covered with ice ; 

 but this would have caused south-west winds over Great Britain, 

 and have prevented the permanent existence of an ice-sheet in these 

 islands. If Europe and North America had been glaciated at the 

 same time, which for the reasons given, however, seems improbable,, 

 the Icelandic cyclone, which now lies (statistically) in winter near 

 to the south-east coast of Greenland, would have been forced to 

 the south ; but the further south it went the warmer would have 

 been the southerly winds which blew east of its centre towards 

 Great Britain and Western Europe. Conditions similar to those 

 which may have prevailed during the maximum glaciation of North 

 America occurred during the early part of 1899 — for information as 

 to which the author desires to acknowledge his indebtedness to 

 Mr. W. N. Shaw, E.E.S., of the Meteorological Office. At that 

 time a great low-pressure system, which sometimes extended from 

 Europe to America, and from Iceland to the Canary Islands, 

 occupied the North Atlantic. Vast volumes of cold air from the 

 Arctic regions were consequently poured over North America, while 

 Western Europe was flooded by warm aerial currents from the 

 sub-tropical zone. At the beginning of February temperatures of 

 from —40° F. to —60° F. were commonly registered in different 

 parts of North America ; at the same time the thermometer rose in 

 London to 66° F., in Liege to 70° F., and in Davos, more than 

 5,000 feet above the sea, to 62° F., the average maximum for that 

 month at the latter place being 38° F. For some weeks storms of 

 exceptional violence occurred almost daily in the Atlantic. These 

 coincident phenomena are directly traceable to the same cause. 



No meteorological difficulties arise if we adopt the hypothesis that 

 glacial and interglacial periods alternated in the eastern and western 

 continents. If the ice-cap extended from Greenland to Scandinavia, 

 the North Atlantic cyclone would have been forced to the south-west, 

 towards the American coast, producing warm south-east winds over 

 Labrador ; if, on the contrary, it stretched from Greenland to North. 





