DIRECTION AND VELOCITY OF WIND. 
33 
the wind was from north to east. , For the years mentioned, when 
there were bad woodland infestations in Massachusetts, the wind 
during the hot days was usually southwest, which would be most 
favorable for the spread of the insect into the region where it has 
since been found in scattered colonies. 
The relation of temperature and the direction and velocity of the 
wind are intimate, as shown by the tables which follow. 
It has been stated that wind spread is possible when the tempera- 
ture as recorded by the Weather Bureau is as low as 65°, but an 
increase in temperature makes the chances of spreading greater. 
Tables IV and V give the direction of the wind for the different 
years, at the Boston Weather Bureau station when the temperature 
was 65° or higher, and the wind velocity 10 miles per hour or more. 
In all cases where the temperature is 70° F. or above, italic letters 
and figures are used in the columns of the table giving the tempera- 
ture and the direction and velocity of the wind. Otherwise the letters 
and figures are in Roman. 
Table IV. — Temperature and direction and velocity of wind on dates after hatch- 
ing of gipsy-moth caterpillars, 1902-1911. 
(Data from U. S. Weather Bureau at Boston, Mass.) 
Date. 
1902. 
Apr. 21 
23 
24 
26 
28 
29 
May 5 
7 
8 
9 
13 
14 
24 hours. 
AM 
PM.AM 
AM 
AM 
AM,PM 
AM,PM 
AM 
AM,PM 
AM,PM 
AM 
AM 
AM 
Maxi- 
mum 
tem- 
pera- 
ture. 
Direc- 
tion of 
wind. 
W... 
w... 
w... 
sw. 
NW. 
s.... 
sw. 
s.... 
sw. 
w... 
N... 
w... 
Velocity 
of wind. 
Miles per 
hour. 
12 
29 
26 
32 
18 
Date. 
1902. 
May 16 
17 
18 
21 
22 
23 
24 
25 
26 
27 
30 
31 
24 hours. 
AM,PM 
AM 
AM,PM 
AM 
AM,PM 
AM,PM 
AM,PM 
AM,PM 
AM,PM 
AM 
AM 
AM 
Maxi- 
mum 
Direc- 
tem- 
tion of 
pera- 
wind. 
ture. 
°F. 
72 
W. 
70 
N 
78 
NW..... 
72 
SW 
80 
SW 
88 
SW 
84 
sir 
76 
sw....: 
80 
sw 
71 
s 
69 
w 
65 
sw 
Velocity 
of wind. 
Miles per 
hour. 
20 
18 
14 
16 
23 
19 
U 
24 
26 
20 
33 
17 
Note.— During the years 1902, 1903, and 1904 the Boston Weather Bureau did not record temperature s 
hourly, but took readings at 8 am and 8 pm each day. AM in the table refers to the reading made fo r 
the period from 8 am to 8 pm, while PM covers the following 12 hours. The direction of the wind and 
its maximum velocity did not necessarily occur when the temperature was at the maximum, for the tem- 
perature may have been 65° or even less at that time. 
Date. 
24 hours. 
Temper- 
ature. 
Direction 
of wind. 
Velocity 
of wind. 
1903. 
Apr. 28 
29 
AM 
°F. 
66 
83 
83 
75 
69 
70 
n 
70 
67 
S 
NW. 
Miles 
per hour. 
13 
AM,PM 
19 
30 
AM 
S W. . . 
28 
May 10 
11 
AM 
s 
s 
s 
19 
AM 
13 
12 
AM 
13 
13 
AM 
s 
14 
AM 
E 
18 
15 
AM 
SE 
10 
00474°— Bull. 119—11 
