THE CLIMATE OF GREAT BRITAIN. 269 



it reaches its greatest northerly range near the Eocky 

 Mountains. 1 Thence it turns sharply southwards, 

 crosses Vancouver's Island, sweeps nearly to latitude 

 45 in the central part of the Pacific, whence passing 

 slightly northwards it crosses the southern part of 

 Saghalien Island. Here it turns sharply northwards, 

 crosses that very district of Siberia which, in Fig. 1, 

 is occupied by the isochimenal of intensest winter cold, 

 traverses Siberia, and passes near St. Petersburg, through 

 Berlin and Amsterdam to London. 



The relations thus presented by the isotheral of 

 London are precisely the reverse of those exhibited 

 by the isochimenal. The isotheral forms a closed 

 irregular oval, whose greatest length lies on the two 

 oceans : here it falls outside the line of mean annual 

 heat, while on the continent it falls far within this 

 line. 



In another respect the isotheral presents a note- 

 worthy contrast to the isochimenal. While the latter 

 encloses an area largely exceeding the area enclosed by 

 the mean annual line, the isotheral encloses an area 

 noticeably smaller. 8 



A tendency to break up into two curves is exhibited 

 in the isotheral, even more markedly than in the two 

 other curves. But singularly enough, here, where one 



1 It is noteworthy that the minimum distance of the isotheral from 

 the North Pole here attained is exactly equal to the minimum distance 

 of the isochimenal from the equator. 



2 Here an important advantage of the isographic projection is ex- 

 hibited. The relation pointed out is altogether obliterated in Mercator's 

 projection, and could only be roughly inferred from any but an isographic 

 projection. 



