118 



WIND. 



Ill r.oiineotioii w itl^ an investigation into the velocity equivalents of the Beaufort Scale * 

 mafle by the writer in 190-J, a tlctcnnination of gustiiiess was inoidcntally made for two coast 

 stations in the British Isles, viz., Scilly Isles and Holyhead. 



The "ustincss was only investigated with reference to the average velocity and no account 

 was taken ol wind direction or season. The mean value was also obtained from all hours 

 hence it is soni(-.what greater than the value which would have been obtained if the method 

 used in this discussion had been followed. The result showed that at both stations the gusli- 

 ness was the same and was indepciuh^nt of wind velocity. The mean gustiness f(.r all velo- 

 cities was found to be (38. In other words the average difference between the highest gust 

 in an hour and the lowest lull was -08 times the mean velocity. As this is the only determin- 

 ation of this nature of which I am aware we must take it as the standard with which to 

 compare our Antarctic results. 



The Antarctic records have been worked up for the twelve months, Maich, 11)11, to 

 February, lUTJ, inclusive. 



The mean gustiness for the jMirind was 1-U4. 



Thus the conclusion reached by an inspection of the traces is confirmed : the winds at 

 Cape Evans are more gusty than those on the coast of tlreat Britain in the ratio of ru4 

 to "08 which ratio would have been still further increased if the British records had been 

 reduced by the method used for the Antarctic records. 



Wiile in the Antarctic we soon noticed the characteristic difference in the gustiness of 

 northerly anil southerly winds shown on figures 38 and 39, and we could as a rule determine 

 the direction of the wind from an examination of the anemometer trace without going outside 

 the hut. Whenever the trace was uniform without marked gusts and lulls we knew that the 

 wind was from the north while a gusty wind was nearly always from the south. 



By examining the mean gustiness of northerly and southerly winds separately we find that 

 southerly winds are more gusty than northerly winds, and the higher the mean velocity the 

 more the "ustiness of the southerly winds exceeds that of the northerly winds, this is shown 

 by the last line of table OG which gives the ratio of the gustiness of winds for different velocities. 



Table 6(3. 

 Gudiness of W Ind (tccurdiiuj to Mean Velocihj. 



The gustiness of the wind at Scilly and Holyhead was foimd to be the same for all 

 velocities ; this however was not so at Cape Evans for table 66 shows that with an increase 

 of velocity for both northerly and southerly winds the gustiness decreases. This does not 

 mean that for high \\'inds the actual difference in the velocity of gusts and lulls decreased, but 

 that the ratio of this difference to the mean velocity decreased. Thus for a wind of 15 miles 

 an hour the average difference between gust and lull was 1.5x 1'16=17'4 while for a velocity 

 of 4.J miles an hour the corresponding difference was 4.JX'90=40 5, hence while the actual 

 difference in the wind changes increased from 17-4 to 40") the gustiness fell from I'Ki to -flO. 



The gustiness of the wind varied considerably during the year. 



* a. ('. Siin])son : " TIk; Beaufort Sctie of Wind Furce," M. I). iNo. ISO. 



