266 LIGHT SCIENCE FOR LEISURE HOURS. 



ing 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 indi 

 cated in Figs. 1 and 2 by two black spots, one north 

 of the American, the other north of the Asiatic con 

 tinent. It is to be noted, however, that at the American 

 pole the mean annual temperature is not quite so low 

 as at the Asiatic pole, the former temperature being 

 3i, the latter 1 Fahrenheit. 



Eeturning to our subject, let us consider the all- 

 important question of range of climate. The effects 

 of climate, unimportant to the stronger inhabitants of 

 a country, but largely influencing the health and com 

 fort of the majority, are chiefly felt through the changes 

 that occur during the year. Now, we have seen that 

 the line of mean annual temperature of England departs 

 in a very marked manner from coincidence with a 

 latitude-parallel ; but we shall find the lines indicating 

 the extreme temperatures of the year much more 

 irregular ; and the peculiarity of climate, which their 

 conformation illustrates, much more important. 



In Fig. 1 the isochimenal, or the line of equal winter 

 heat, through London, is indicated by a strongly marked 

 closed curve. Its form is remarkable. It passes nearly 

 in a north and south direction, along the length of 

 England and Scotland, approaches singularly near 

 to Iceland, but turns sharply southwards and travels 

 across the Atlantic in a direction which brings it to 



