268 LIGHT SCIENCE FOR LEISURE HOURS. 



pole of the earth.' I cannot but think that this is a 

 mistake. I believe that if the isotherms traced, in 

 part, in Fig. 1 could be completed, they would be 

 found to form two ovals. The American oval would 

 enclose the American pole of mean temperature, but 

 very eccentrically, showing that the pole of extreme 

 winter temperature lay westwards and southwards, pro- 

 bably near Victoria Land. The Asiatic oval would 

 not probably enclose the Asiatic pole of mean tempera- 

 ture ; and the position indicated for the Asiatic pole 

 of extreme winter cold lies on or near the Arctic circle, 

 where it is crossed by the river Lena. At the true 

 pole of the earth the extreme winter cold is probably 

 not nearly so intense as the cold at either of the points 

 here indicated. 



From the direction of the isochimenal through Lon- 

 don, it is evident that the Eastern Counties and Kent 

 experience the coldest winters of all places in the 

 British Isles, while Cornwall and the south-westerly 

 parts of Ireland enjoy the mildest winter climates. 

 In fact, winter in Cornwall is not more severe than in 

 Constantinople ; and in south-west Ireland the winter 

 is still milder, approaching, in this respect, to the 

 winter climate of Teheran. 



The contrast, when we turn to the isotheral of Lon- 

 don, is remarkable. Instead of travelling nearly north- 

 wards, this curve passes in a south-westerly direction, 

 reaching its greatest southerly range in the central 

 part of the Atlantic Ocean; thence it travels with a 

 northerly sweep through Nova Scotia and Canada, till 



