THE SCOTTISH NATIONAL ANTAECTIC EXPEDITION. 



273 



Ttikiug seasonal values, the mean amount of cloud is 7 '9 in Spring, 9 '2 in Summer, 

 8 "3 in Autumn, and 7 '4 in Winter. It will be seen that in no month did the per- 

 centage of hours with a completely overcast sky fall below 54, while in January 88 per 

 cent, of the observations showed a sky entirely overcast. Cloudless hours are at a 

 maximum in June, with 157 cases forming 22 per cent, of the whole ; but in December 

 the sky was cloudless on only two hours and in Janu;iry on one hour. For the period 

 April to December 1904, the mean amount of cloud is as follows : — 



The diurnal period in the amount of cloud is shown in the following table : — 



Mean Amount of Cloud. 



Thus, on the mean of eleven months cloud is above the average from 7 A.ivr. to 5 p.jm. 

 and below the average from 8 p.m. to 5 a.m. There is a double period, there being 

 maxima at about 9 a.m. and 3 P.M. and minima at 3 A.M. and 9 p.m. The most marked 

 diurnal range occurs in Spring, when the increase of cloud as the temperature rises 

 results in a decided maximum from noon to 2 p.m., while the clearing of the sky at night 

 is shown by a minimum from midnight to 3 a.m. In Summer and Winter the diurnal 

 range is not well marked. (See Plate III.) 



