THE SCOTTISH NATIONAL ANTAECTIC EXPEDITION. 



Mean Strength of Wind with the Different "Winds. Scale 0-12. 



279 



Thus the strongest winds are from the north-west and the lightest from the east, so 

 that the barometric gradients at the South Orkneys must be quite diflferent from those 

 further south, where the strongest winds are from the east, while north-west winds are 

 of average strength.* Indeed, the South Orkneys are within the " west wind system," 

 which dominates the weather conditions in the South Atlantic, Indian and Pacific 

 Oceans south of 40° S., although at times, especially in Winter, the South Orkney 

 Islands, owing to the freezing up of the sea to the south, do come under the influence 

 of the polar anti-cyclone, depressions which usually pass to the south then taking a 

 more northerl}' course. (See Plate I.) 



Visibility. 



From 10th May 1903 until 21st February 1904 the visibility was noted at every 

 hour on a scale of 0-12 miles. As the horizon was only open to the north-west and 

 south-east, the visibility in these two directions was assumed to be the mean. The 

 following table shows the mean and extreme values for the months : — 



* See " Some Meteorological Results of the Scottish National Antarctic Expedition," Scottish Geographical Journal 

 for May 1906, vol. xxii. p. 257. 



VOL. IT. 38 



