2 9 o rOPTJ.AR LECTURES AND ADDRESSES. 



experience ;i prevalence of South-west winds in 

 the Northern hemisphere, and North-west winds in 

 the Southern hemisphere. The thermal estimates 

 which we have just had under consideration show 

 that these poleward winds must in all possible 

 conditions as to distribution of land and water, 

 have a great direct influence in moderating the 

 cold of the northern regions. They contribute 

 also largely towards the same result by increasing 

 the oceanic circulation, and would do so to a still 

 greater degree if there were less of land than 

 there is in the circumpolar and temperate regions. 



Now wh'at must be the climate of a small island 

 in an open icclcss circumpolar sea ? Temperate 

 and quite free from frost except in hollows, we 

 may I think safely answer. The water and air 

 all round it nrc above the freezing point, and the 

 air is saturated or nearly saturated with aqueous 

 vapour. Wells' old theory of dew now helps us. 

 \Yhcn the sun is below the horizon the upper 

 surface of the earth whether it be rock or stones 

 or soil, or blades of grass or leaves of trees 

 whatever is unscreened from above, radiates as 



