264 LIGHT SCIENCE FOR LEISURE HOURS. 



to possess when we come to consider the extreme 

 range of temperature during the year. In fact, Eng- 



FIG. i. 



Northern hemisphere on an equal-surface projection, showing curves of 

 mean annual and midwinter temperature through London. 



land is thus brought to the centre of the true temperate 

 zone of the northern hemisphere ; and the considera 

 tion of Figs. 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 circumstance, not immediately connected with the 



