68 THE VOYAGE OF H.M.S. CHALLENGER. 



region. The low temperature region in Siberia shows a mean temperature of -55° - 5 at 

 Werkojansk, near its centre. In North America, near the magnetic pole, temperature 

 falls a little below -25°. 



The influence of oceanic currents on the isothermals is strikingly seen through the 

 centre of the Atlantic, and thence round the North Cape into the Arctic Ocean east- 

 wards as far as the Liakov Islands. The influence of Hudson's Bay, the North Seas, and 

 the Baltic with its connected seas, are particularly well illustrated in this month ; and, 

 on the other hand, the influence of the land in lowering the winter temperature is 

 equally well seen along the centre of the unbroken land surface of Europe from 

 Moscow to Lisbon. 



The observations made in December by various expeditions to Antarctic regions 

 show a mean temperature of 25° between longs. 160° E. and W., and similar low 

 temperatures occur in this zone in the other summer months of the southern hemi- 

 sphere, being in this respect quite different from the Arctic regions in summer where 

 mean temperature does not fall below 35°, even though observations are available from 

 much higher latitudes. The difference is, of course, due to the all but continuous 

 covering of water, ice, or snow within the Antarctic Circle, whereas within the Arctic 

 Circle there is a large proportion of land, and the Arctic Ocean is, besides, nearly 

 altogether landlocked. 



The Loffoden Isles and Werkojansk are approximately in the same latitude, yet 

 their mean temperatures are respectively 30° and -55°, the difference being 85°. This 

 shows in an impressive manner how the temperature does not fall according to 

 latitude, but according to the distance to which the place is situated eastward and 

 northward in the continent ; where, at the same time, the air is calm, dry, and clear, 

 and seldom reached by winds from any ocean. 



Another feature of the isothermals is their openness in those regions of Europe and 

 western Asia, where south-westerly winds prevail, and their crowded condition over 

 the higher plateaux to the south to which these winds do not reach, and where the air 

 is drier and calmer. 



The highest isothermals are 95° in the north of Australia, 90° in South Africa, and 

 85° in two districts in South America separated by the valley of the Plata. The 

 crowding of the isothermals in South America and South Africa is characteristic of all 

 regions where in summer the air is dry, and where the adjoining coast is swept by winds 

 passing into lower latitudes. 



Pressure has fallen everywhere over the southern hemisphere, and over Turkey, 

 Russia, Scandinavia, and thence westward across Iceland, Greenland, and Arctic 

 America ; but elsewhere it has risen. 



A much greater expanse of the Arctic regions is overspread by a high pressure ; the 

 centre of the anticyclone of Asia shows now a pressure of 30 - 50 inches ; that of North 



