FE. Loomis— United States Weather Maps. 7 
be obtained in the north quadrant, or the number of observa- 
tions was too few to furnish a reliable mean. The following 
table shows the average velocity of the wind in the different 
quadrants, according to these observations. 
W. quadrant. §.quadrant. E.quadrant. WN. quadrant. 
0-1 8°8 8-3 76 
It will be noticed that the velocity is greatest in the west 
quadrant, and that the velocity diminishes in the successive 
quadrants as we pass round the circle from west by south to 
north. 
The observations were then divided into two classes, one 
containing those cases in which the rate of progress of the 
storm was greater than the mean, and the other containing the 
cases in which the rate was less than the mean, aud the aver- 
ages were taken both of the velocity of the storm’s progress 
and the velocity of the wind in ‘the east and west quadrants of 
the storm, when the following results were obtained. 
a ee ae 
32-1 8 9-0 
18° 78 113 ; 
These numbers indicate that the stronger the wind on the 
west side of the storm, the less is the velocity of the storm’s 
progress. The velocity of the wind in the west quadrant gen- 
erally exceeds the velocity in the east quadrant by 22 per cent. 
When the velocity in the east quadrant is equal to that in the 
west quadrant, the velocity of the storm’s progress is seven 
miles per hour greater than the mean; but when the velocity 
of the wind in the west quadrant exceeds that in the east quad- 
rant by 44 per cent, the velocity of the storm’s progress is 
seven miles per hour /ess than the mean. 
_ Some persons might have anticipated that an increase in the 
velocity of the wind in the western quadrant of a storm would 
have the effect of driving the storm eastward more rapidly ; that 
is, of increasing its velocity. But we shall see hereafter that 
upon each side of a storm’s center the wind blows obliquely in- 
ward, and hence we must infer that in the central region of the 
storm there is an upward motion of the air: and this is the 
cause of the precipitation of vapor; that is, the cause of the 
rain-fall, An increase in the velocity of the wind in the west- 
ern quadrant is accompanied by an increase in the velocity of 
the upward motion in this quadrant; that is, an increase of pre- 
cipitation. This increased precipitation of vapor tends to depress 
the barometer on the western side of the storm; that is, tends 
to retard the eastward motion of the storm’s center; and this 
cause may operate with sufficient force to eaniy the storm's 
ne : : 4 
center westward, as actually happened in several instances in 
