SNOW-WAVES AND SNOW-RIPPLES 203 



concerned, the flood tide is far more effective than 

 the ebb. 



On the Action of an Obliquely Crossing Wind upon 

 the Swell of the Sea. 



My observations upon the different effects pro- 

 duced upon sand and snow by wind-eddies with 

 horizontal and vertical axes respectively led me to 

 notice certain effects of wind upon water waves. 



The following observations relate to two different 

 conditions of the commencement of the wave- 

 making action of wind upon water ; first when 

 there is a swell — i.e., pre-existing waves, already 

 running in the direction of the wind ; second, when 

 the following wind blows obliquely across the 

 swell. 



First Case. — On December 20, 191 1, I was on 

 the P. and O. s.S. Egypt, not far from Cape 

 Finisterre, homeward bound. There was a heavy 

 westerly swell, of which I took measurements at 

 3 p.m. Its length was 640 feet, speed 39-8 statute 

 miles per hour, and height about 20 feet. During 

 the ensuing night the wind came on to blow very 

 hard in precisely the direction in which the swell 

 was running. The force of the wind at 4 a.m. on 

 the 2 1st was between 9 and 10 of Beaufort's scale, 

 or 48- 5 statute miles per hour. We were at this 



