116 The Climate of Great Britain, 



presented on a projection (the equi^raphic) which has been 

 already discussed in these pages.* The smallness of the scale 

 would not readily permit of the introduction of the system of 

 isothermal lines usually presented, therefore I have only intro- 

 duced 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 north- 

 wards, 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 

 isotherm nowhere has a higher latitude than where it crosses 

 the British I sles ; 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 Eng- 

 land will be seen to possess, when we come to consider the 

 extreme range of temperature during the year. In fact, 

 England is thus brought to the centre of the true temperate 

 zone of the northern hemisphere ; since the consideration of 

 Eigs. 1 and 2 will show that the isotherm of London approaches 

 as near to the tropic of Cancer in one part of its course, as to 

 the Arctic circle in another. 



Before leaving this part of the subject, let me note a cir- 

 cumstance, not immediately connected with the climate of 

 Great Britain, but geographically interesting. In examining 

 the polar presentation of the London isotherm, we see that in 

 two parts of its course it exhibits a tendency to travel north- 

 wards, and becomes, in fact, convex towards the pole. If we 

 traced in isotherms of greater mean temperature — that is, 

 nearer the equator — we should find this peculiarity gradually 

 diminishing. But if we traced in isotherms of lower mean 

 temperature, we should find the convexities gradually becoming 

 sharper and more defined, approaching each other more and 

 more nearly, until finally they would meet, and the isothermal 

 curve be divided into two irregular ovals. Proceeding to trace 

 out curves of still lower temperature we should find the two ovals 

 closing in towards two poles of cold. These are indicated in 

 Figs. I and 1 by two black spots, one north of the American, 

 the other north of the Asiatic continent. It is to be noted, 

 however, that at the American pole the mean annual tempera- 



* See the number for July, 1866. Tbe term isographic is etymologically 

 preferable to the hybrid word equigraphic. 



