NORTHUMBERLAND AND DURHAM. 51 



mean temperature falls as we ascend the hills at the rate of 1° 

 for every 100 yards. For the interior of the country, from 

 London northward to Edinburgh, we may take from 47° to 49° 

 as a fair average, 47° for the South of Scotland, 48° for the North 

 of England, and 49° for the Midland counties : the difference 

 between summer and winter being usually from 18° to 20°. On 

 the sea coast the difference between summer and winter is smaller 

 than in the interior, and the mean temperature generally a shade 

 higher ; but in our table this last character, as between By well 

 and Shields, does not hold good. We will take then the annual 

 average of our Lower zone at from 48° to 45°, of the Middle zone 

 at from 45° to 42°, and of the Upper one at 40° or 41°. 



The great characteristic of the climate of Britain, as compared 

 with that of other parts of the JSTorth Temperate zone, is its equa- 

 bility, the absence of extreme degrees of either heat or cold, and 

 the consequent smallness of the difference there is between winter 

 and summer. We shall see shortly what an important influence 

 this has upon the distribution of plants. Even within the com- 

 pass of England we can trace palpably the influence of the sea in 

 cutting off the extremes in both directions. Of course, it is on 

 the west side of the island that this influence operates most power- 

 fully, and we see from the table just given, that although Helston 

 is 6° warmer in winter than Greenwich or York, it is rather colder 

 than the former and only 1^° warmer than the latter in summer; 

 at Shields and Alnwick that the difference between summer and 

 winter is only 16° and 14°. The winter is not materially colder 

 at I^ewcastle than at London ; but all the other seasons are, 

 though the difference, when expressed in figures, is probably 

 much smaller than any one who has not studied it as a question 

 of figui-es will be likely to suppose. The summer is warmer in 

 the interior of the south-east of England than anywhere else in 

 Britain, rising in some places to an average of a little over 60°. 

 The autumn, both in the north and south, comes very near to 

 the average of the whole year, being generally a little above it. 

 But if we turn to the Continent, we shall see how much colder 

 the winters and warmer the summers arc in proportion, and how 

 the divergence increases as we pass into the interior. 



