The Climate of Great Britain. 121 



attributes to oceans and continents respectively. With this 

 change — somewhat a bold one, I confess* — we may say that 

 all the non-variable causes tending to exalt temperature 

 operate in England's favour. 



The constant causes tending to lower temperature are 

 simply the converse of those above considered. 



Of variable causes increasing temperature, the principal are 

 a serene sky in summer, and a cloudy sky in winter. It may 

 appear, at first sight, paradoxical to assign opposite effects to 

 a cloudy sky. It must be remembered, however, that clouds 

 considered with reference to temperature, have two functions : 

 they partially prevent the access of heat to the earth, and they 

 partially prevent the escape of heat from the earth. Now, 

 in summer the first-named influence is more important than 

 the second : the days are longer than the nights ; that is, the 

 earth is receiving heat during the greater part of the time in 

 summer. A cause, therefore, which affects the receipt of heat 

 is more important than a cause affecting the escape of heat. 

 On the other hand, in winter, the nights are shorter than the 

 days, and the influence of clouds in preventing the escape of 

 heat becomes more important than their effect on the receipt 

 of heat.f In fact we may compare the influence of clouds to 

 the effects of certain kinds of clothing ; flannel, for instance, 

 is as suitable an article of dress for the cricketer as for the 

 skater. 



Now the climate of England is remarkably humid both in 

 winter and summer. And this humidity is shown, not so 

 much by the quantity of rain which falls, as by the frequent 

 presence of large quantities of aqueous vapour in the atmo- 

 sphere. Skies, even, which we in England consider clear, are 

 overcast compared with the deep-blue skies of France or Italy. 

 What the influence of these humid palls may be " on the out- 

 flow of moral sentiments " which Humboldt considered to be 

 so favourably influenced by transparent skies, I shall not here 

 pause to inquire. It is clear, however, that the influence of our 

 cloudy skies tends to modify the severity both of our winter and 

 our summer seasons; and these benefits are so great that we may 



* Not unsupported, however, by good authority. Thus Professor Nichol, 

 speaking of the climate of Europe, writes : " The air that rises in Africa blows 

 rather over Asia than Europe. The cradie of our winds is not in Sahara but in 

 America." Again, Kaemtz notices, that if the effects of oceans and continents 

 were those assigned by Humboldt, we should find in the western parts of America 

 a colder climate than in the eastern parts ; the reverse, however is the case. 



f Gilbert White noticed long ago — apparently without understanding — the 

 influence of a clouded sky on the temperature. " We have often observed," he 

 says, " that cold seems to descend from above ; for, when a thermometer hangs 

 abroad on a frosty night, the intervention of a cloud shall immediately raise the 

 mercury ten degrees ; and a clear sky shall again compel it to descend to its former 

 gauge." 



