THE CLIMATE OF GREAT BRITAIN. 263 



These lines are usually presented in maps on Mercator's 

 projection, an arrangement which has some advantages, 

 but is not, on the whole, very well suited to exhibit the 

 true conformation of the isothermal lines the study of 

 which, it has been well remarked, constitutes the basis 

 of all climatology. 



In Figs. 1 and 2, the northern hemisphere of the 

 earth is presented on a projection (the equal surface) 

 which has been discussed in my ' Essays on Astronomy.' 

 The smallness of the scale would not readily permit of the 

 introduction of the system of isothermal lines usually 

 presented, therefore I have only introduced the isotherm 

 which passes through London. In both figures this 

 isotherm is represented by a dotted closed curve passing 

 across the south of England, thence across the Atlantic 

 in a south-westerly direction, and across the continent 

 of America nearly on the latitude of New York. After 

 it has entered the Pacific Ocean, the isotherm passes 

 somewhat northwards, but trends southwards again as 

 it nears the Asiatic continent, reaching its greatest 

 southerly range in the sea of Japan, traversing Asia 

 nearly on the latitude of the Aral Sea, and thence passing 

 somewhat northwards through the Crimea, Vienna, and 

 Brussels to London. Along its whole extent the iso- 

 therm nowhere has a higher latitude than where it 

 crosses the British Isles ; in other words, the mean 

 annual temperature of Great Britain is higher than 

 that of any country lying between the same latitude- 

 parallels. The advantage of this arrangement is second 

 only in importance to that which England will be seen 



