E. Loomis— United States Weather Maps. 5 
These numbers clearly indicate that generally when a storm 
is advancing most rapidly, the rain area extends to an unusual 
distance on the eastern side of the storm, and the velocity of 
the storm’s center appears to increase more rapidly than the 
extension of the rain area. e average extent of the rain 
area on. the east side of the storm’s center is 500 miles. When 
the rain area extends more than 500 miles on the east, the 
storm advances with a velocity greater than the mean; but 
when the extent of the rain area is less than 500 miles, the 
storm advances with a velocity less than the mean. If we con- 
fine the comparison to the two divisions which correspond to the 
greatest and least velocity, they lead us to conclude that when the 
eastern extent of the rain area is 100 miles greater than the mean, 
the hourly velocity of the storm’s progress is increased 149 miles; 
but when the eastern extent of the rain area is 100 miles less 
than the mean, the hourly velocity of the storm’s progress is 
diminished 8-1 miles. ; 
In order to determine the influence of the rain area upon the 
direction of the storm’s path, I attempted to determine not sim- 
ply the limits of the ram area, but the direction in which the 
rain area was most extended. The rain area is usually of an 
oval form, as show in the preceding figure. For each rain area 
a line was drawn dividing the area symmetrically, so as to 
represent the longer axis of the oval, and the bearing of this 
ine was measured with a protractor. I then selected those 
cases in which the direction of the storm paths was most north- 
erly, and also those cases in which the direction was most 
southerly, and for each case the position of the axis of the rain 
area was determined. I then determined the average direction 
of the storm paths and the average direction of the axes of the 
rain areas for each class of cases, and obtained the following 
results. 
Course of storm. Axis of rain area. 
N. 40° E. N. 53° E. 
N.116 E. N.118 E. 
storm is most southerly, the inclination of these two lines is 
only two degrees. Considering that there is a difference of 76 
in the mean direction of the storm paths for the two classes of 
cases, and a difference of 65° in the position of the axes of the 
rain areas, we may conclude that the average course of the 
storm paths for 24 hours coincides very closely with the posi- 
tion of the axis of the rain area for the preceding eight hours. 
If the comparison could have been made with the direction of 
the storm paths for the succeeding eight hours, instead of 24 
