22 G. I. TAYLOR ON EDDY MOTION IN THE ATMOSPHERE. 



Except for the kite ascent of July 17th, 1913, the values of K /pcr which, as was shown 

 on p. 14, should be equal to fj.jp, lie between these values.* It is unfortunate that the 

 lack of skilled assistance in flying the kites from the " Scotia " prevented me in most 

 cases from being able to get simultaneous values of K/pa- and /j./p. For the kite ascent 

 of August 2nd, however, I have the following observations : At 350 feet the wind had 

 veered one point from the surface wind. At 770 feet the wind had veered two points 

 from the surface wind, and at all greater heights the veer was two points. It seems, 

 therefore, that at 770 feet, i.e., 230 metres, or at some less height, the wind had 

 attained the gradient direction, so the /u//o lay between 0'77 x (23,000) 2 x 10~ 5 or 

 4'0x 10 :i and 0'77 x 10 3 . On referring to Table I. it will be seen that the value of 

 K/pa- on that occasion was 2'5xl0 3 . These results certainly tend to confirm the 

 theoretical deduction that KJpa- = ftfp, but more evidence is wanted before the point 

 can be regarded as finally settled. 



On p. 13 it was shown that /n/p ^(wd). The size of the eddies, which produce the 

 effects we have been considering, are evidently governed by d. We may say roughly 

 that d is less than the average diameter of an eddy ; if therefore we could measure w, 

 we should be able to determine the size of the eddies. Now Mr. J. S. DINES has made 

 a large number of observations of small vertical gusts with tethered balloons. On 

 p. 216 of the Technical Report of the Advisory Committee for Aeronautics is shown a 

 trace which represents the vertical component of the wind velocity at any time during 

 a certain interval of five minutes, on January 19th, 1912. The average wind velocity 

 during the interval was 7 metres per second ; and I find from the trace, which Mr. DINES 

 says is typical, that the average deviation from the mean vertical velocity (the mean 

 wind was not quite horizontal) was 25 cm. per second. We may take this as w. 

 Assuming that the gradient direction was attained at a height of 800 metres the 

 value of -%(wd) would be 50 x 10 3 or wd = 10 5 approximately. 



Hence 



10 5 

 d = = 4 x 10 s cm. = 40 metres. 



aO 



The wind was blowing with velocity 7 metres per second so that it would cover 

 7x60 = 420 metres, or about 10 times d, in a minute. If the vertical and horizontal 

 dimensions of an eddy are about the same, this would mean (since d is less than the 

 diameter of an eddy) that rather less than 10 eddies would pass a given spot in a 

 minute. On examining Mr. DINES' trace it will be found that there are roughly 

 about 6 peaks per minute on the curve representing vertical velocity. 



These calculations are very rough, but they do show at any rate, that actual 

 observations of eddy motion do not involve anything that is contrary to the 

 assumptions on which the theory contained in this paper is based. 



* See Table I. 



