114 



WIND. 



During three-quarters of the wliole period the wind was blowing from the Barrier through 

 McMurdo Sound, during a little more than half of the remaining period the wind was blowing 

 from a northerly direction, and during the rest of the time the air was entirely still. The 

 average veloeit\' of the wind from the south was nearly twice that of the wind from the 

 north. The total flow of air from the south was nearly nine times that from the north. 

 All of which shows the predominant part played by the winds fioin the south. 



Later on we shall have occasion to study in greater detail the weather conditions which 

 accompanied the two types of wind and also the causes which give rise to them. For this 

 purpose it is useful to group the observations not only according to direction but also accord- 

 ing to velocity. As already stated the recording wind vane was not very satisfactory for 

 low velocities, but above a velocity of 10 miles an hour the direction record during nineteen 

 months is practically complete. It has therefore been decided to tlivide the winds having 

 velocities up to 10 miles an hour into two groups irrespective of direction, these being to 

 5 miles an hour and 6 to 10 miles an hour. Above 10 mile,s an hour the winds of each 

 direction have been grouped into two classes of («) II to 30 miles an hour and (b) above 

 30 miles an hour. As these groups will be used very frequently it is convenient to give here 

 a table showing the number of observations which fall under each head. 



Table 65. 

 The number of Observations in the six Chief (rroups of Wind. 



