THE SCOTTISH NATIONAL ANTARCTIC EXPEDITION. 



281 



4 P.M., with maxima at 4 A.M. aiul 2 p.m. The first minimum is probably due to the 

 occurrence of fog and mist in the early morning, while the afternoon minimum is related 

 to the condensation setting in after the temperature has begun to fall. 



Mean Hourly Visibility, May 1903 to February 1904. Scale 0-12. 



* Mean of May, 22 days ; of February, 21 days. 



Humidity of the Air. 



Owing to the great doubt that attaches to the behaviour of the wet bulb thermometer 

 at and below the freezing point, I have considerable diffidence in bringing forward the 

 following data. After consultation with the leading British meteorologists, including 

 the late Dr Buchan and Dr W. N. Shavp, it was considered inexpedient in any case to 

 attempt to deduce humidity values when the temperature of tlie wet bulb fell below 10°. 

 As a considerable number of observations during the Winter and Spring were below 10°, 

 the mean relative humidity for these months has not been determined. In the following 

 table will be seen the hourly depression of the wet bulb for the eleven months and the 

 seasons : — 



Mean Hourly Depression of the Wet Bulb at Laurie Island, South Orkneys, 1903-1904. 



* Mean of 21 days. 



