148 PKOF. E. HULL, LL.D., F.K.S., F.G.S., ON 



(let us say) 32° Fahr. taking the position of that of 42° 

 Fahr., and that of 42° taking the position of that of 52° ; 

 there will, in fact, be a general advance of cold southward. 

 Then by observing the climatic conditions of the regions 

 crossed by the present isotherms of 32° and 42° we shall be 

 able to form an approximate idea of the climate, nnder the 

 hypothetical conditions of temperature we are here con- 

 sidering. I am well aware that this mode of determination 

 would not, in all cases, give strictly accurate results. 

 Climates depend not only on temperature, but on relations 

 of land and sea, on levels, prevalent winds and other con- 

 ditions ; but temperature is a main factor, and the mode of 

 determination here suggested Avill probably afford fairly 

 reliable results. 



Isotherms. — Of all the isothermal lines representing annual 

 mean temperature that may be drawn across the chart of 

 the northern hemisphere, none is more important than that 

 of 32° Fahr., the freezing point of water. This isotherm, 

 according to Berghaus,* crosses America from lat. 58° N. on 

 the west coast, to Cape Charles, lat. 52° 35' N. on the east, 

 skirts the southern coast of Greenland and crosses the 

 Atlantic by the northern coast of Iceland, entering Europe 

 near the North Cape ; then trending southwards along the 

 coast of Norway to the south of the Arctic circle, it crosses 

 the Europe-Asian continent nearly along the 60th parallel 

 to the coast of China. This isotherm is everywhere to the 

 south of the Arctic circle except in that part of the Atlantic 

 bordering the coast of Norway and lying to the south-east of 

 Iceland, where it passes the circle along the arm of the Gulf 

 Stream which, even in these high latitudes, gives evidence 

 of its power to ameliorate the rigour of the climate. 



The isotherm of 32° Fahr. may be regarded as a con- 

 venient line of demarcation between the permanently glacial 

 regions and those which enjoy a temperate climate. To the 

 north of this line are situated the frozen regions of Hudson's 

 Bay, Labrador, Baffin's Bay and Davis Straits (regions only 

 accessible during two or three months in the year), the 

 continental-island of Greenland enshrouded in eternal snow 

 and ice, the Greenland Sea blocked by ice-floes, the glacial 

 isles of Spitzbergen and Franz Joseph Land, Novaia Zemlia 

 and Liakov Isles (New Siberia) with the surrounding Arctic 

 eea, whose surface of ice is only penetrable during three 



Physihalischer Atlas (Gotha, 1892). See map (Plate). 



