99 
during its increase at about 9-32 a.m., and during its decrease 
at about 5-12 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 supports this view. 
The force which acts upon 
the wind during the day 
Mag. Dec. at its principal 
begins to operate about.. 
7-0 a.m. 
Max. East about ......... 
7-48 a.m 
Is at its mean value 
9-32 „ 
Mean position 
9-42 „ 
„ max. „ 
1-26 p.m. 
Max. West 
1-0 p. m 
„ mean „ 
5-12 „ 
Mean position ............... 
5-27 „ 
Ceases to operate or be- 
comes almost inappreci- 
able 
9-0 „ 
Secondary Max. East 
9-54 „ 
With one exception the epochs of the wind force occur 
somewhat 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 inquiry, 
these differences may probably be in great measure due to 
uncompensated errors in the results derived from the indi- 
cations 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 81 ’93 miles in a direction from 
S. 42° 8' W. From these distances and the difference of the 
angles of direction we find that the effect of the additional 
force which acts upon the wind from 7 a.m. to 9 p.m. was 
to impel the air through a distance of 16 ‘3 miles in a direc- 
