454 DR BUCHAN AND MR OMOND ON THE 



This hypothesis agrees with the data given in the table on page 452 for changes 

 due to the selecting fine and cloudy days at the temperate and Arctic stations, except 

 in the cloudy day curve at Sodankylii The monthly values of cloudy days at Sodankyla, 

 however, show that in spring and autumn the usual law of high pressure at night and 

 low pressure during the day holds, and it is only during the winter when the sun is 

 almost absent, and in the height of summer when it is continuously above the horizon, 

 that the cloudy day curve does not agree with that for other stations. 



One other difference between fine and cloudy days is that on the latter rain may 

 fall and not on the former. Several of the selected cloudy days at all the stations 

 w r ere clays on which rain did fall, but the rainfall may be regarded as so equally dis- 

 tributed over the different hours of the day in temperate and Arctic regions that it 

 can hardly effect a purely diurual phenomenon such as is dealt with here. 



