THE FORCING POWER OF RAIN. 253 



unclouded condition of our skies. We believe that, 

 on the whole, the skies have been rather more cloudy 

 than usual this year. The fact that so little dew has 

 fallen is a sufficient proof that the nights have been on 

 the whole more cloudy than usual, since, as is well 

 known, the presence of clouds, by checking the radia- 

 tion of the earth's heat, prevents (or at least diminishes) 

 the formation of dew. The fact would seem to be that 

 the westerly and southwesterly winds which usually 

 blow over England during a considerable part of the 

 year, bringing with them large quantities of aqueous 

 vapor from above the great Gulf Stream, have this 

 year blown somewhat higher than usual. "Why this 

 should be it is not very easy to say. The height of 

 the vapor-laden, winds is usually supposed to depend 

 on the heat of the weather. In summer, for instance, 

 the clouds range higher, and therefore travel farther 

 inland before they fall in rain. In winter, on the con- 

 trary, they travel lower, and hence the rain falls more 

 freely in the western than in the eastern countries 

 during winter. A similar relation prevails in the 

 Scandinavian peninsula Norway receiving more rain 

 in winter than in summer, while Sweden receives more 

 rain in summer than in the winter. But this summer 

 the rain-clouds have blown so much higher than usual 

 as to pass beyond England altogether. Possibly we 

 may find an explanation in the fact that before reach- 

 ing our shores at all the clouds were relieved by heavy 



