214 MR. J. BAXENDELL ON THE 



9 p.m. The intensity of this force as measured by the 

 changes which it produces in the direction and velocity of 

 tlie wind is at its mean value during its increase at about 

 9 h. 32 m. A.M._, and during its decrease at about 5 h. 12 m. 

 P.M. Now these times correspond very nearly with those at 

 which the magnetic declination is at the mean for the day 

 as determined from the Greenwich magnetic observations ; 

 and the idea is therefore at once suggested that the daily 

 variations in the direction and velocity of the wind are 

 probably connected in some way with the diurnal changes 

 of magnetic declination. It will be seen that the following 

 comparison of the two classes of phenomena strongly sup- 

 ports this view. 



The force which acts upon 



the wind during the day h. m. 

 begins to operate about 7 o a.m. 



Is at its mean value 9 32 ,, 



,, max. ,, I 26 P.M. 



,, mean ,, 5 12 ,, 



Ceases to operate or be- 

 comes almost inappreci- 

 able 90,, 



Mag. dec. at its principal h. m. 



max. east about 748 a.m. 



Mean position 942 ,, 



Max. west i o p.m. 



Mean position .- 527 ,, 



Secondax'y max. east 9 54 



With one exception^ the epochs of the wind force occur 

 somew^hat earlier than those of the magnetic variations ; 

 but, considering the nature of the wind observations, and 

 that they only extend over a period of seven years, and 

 have not been reduced with special reference to this in- 

 quiry, these differences may probably be in great measure 

 due to uncompensated errors in the results derived from 

 the indications of the anemograph. 



We have seen that the movement of the wind from 7 a.m. 

 to 9 P.M. was 96'67 miles in a direction from S. 46° 36' W. 

 to N. 46° 36' E. ; but if the direction and velocity which 

 prevailed from 9 p.m. to 7 a.m. had continued unchanged 

 from 7 a.m. to 9 p.m., the movement during the latter 

 interval would have been only 81 '93 miles in a direction 

 from S. 42° 8' W. From these distances and the difference 



