126 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 
this shows that the difference between the highest and lowest mean for 
January in the series of years was 24°.2. By reference to the Brecken- 
ridge record in Table VI it will be seen that the lowest January mean was 
in 1875 (— 9°.5), while the highest was in 1878 (+ 14°. 7) ; the difference be- 
tween these two is 24°.2, as given in the above table of extreme varia. 
tion of monthly means. The right-hand column shows the average of 
all the stations for each month. 
The value of this table consists in the fact that it shows at a glance 
the months in which the greatest variations occur. This is, as is well 
known to all who have made meteorology a study, in the winter half of 
the year ; but reference to the column of averages shows that in the 
West and Northwest this is true to an unusual degree, the average varia- 
tion for the winter half (from November to April) being 1C°.8, while for 
the summer half (from May to October) it is only 6°.G. 
If we confine the examination to the northwestern stations, Breck- 
inridge, Fort Sully, Yankton, Fort Benton, Pembina, Virginia City, 
and Bismarck, we find the averages to be as follows: January, 21°.9; 
February, 24°.7; March, 23°.3; April, (P.9; May, 7°8; June, 7<M; 
July, 5°.5; August, 4°.5; September, 7°.G; October, 7°.0; November, 
11°.9 ; December, 22°.7 ; the average of the winter half of the year, 
19°.l, and of the summer half, G°.G, showing the difference to be still 
greater. 
But in order to apply the law which these figures appear to indicate 
more directly to the subject under discussion, we present here a table of 
a similar kind, made up from the same series of years, differing from the 
last only in the fact that it shows the greatest variation between the 
monthly means of two consecutive years. 
Table LX. — Greatest variations between monthly means of two consecutive years. 
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January 
15.8 
18.6 
18.3 
10.7 
17.4 
19.0 
18.7 
10.3 
17.9 
14.7 
22.5 
16.4 
21.4 
16.8 
17.03 
February 
17.2 
19.0 
18.2 
16.3 
16.9 
19.2 
16.0 
4.2 
5.9 
7.6 
8.5 
21.9 
5.3 
21.6 
14.13 
March 
24.0 
7.9 
14.9 
14.4 
17.7 
20.7 
12 5 
7.9 
10.8 
8.4 
18.0 
27.9 
8.5 
21.4 
15.36 
7.1 
4.7 
6.3 
6.8 
6.5 
4.9 
7.6 
7.9 
5.5 
0.3 
4.4 
12.4 
3.3 
7.2 
6.49 
8.2 
8.7 
7.9 
7.6 
5.7 
7.1 
4.3 
3.3 
7.4 
8.6 
6.8 
8.9 
4.0 
6.1 
6.76 
6.0 
4.5 
.4.6 
2.5 
5.3 
5.1 
5.5 
3.7 
*18 
4.6 
1.8 
8.0 
5.8 
2.4 
5.56 
or 
4.58 
3.2 
5.3 
6.4 
5.6 
4.2 
3.7 
5.3 
4.9 
7.8 
8.3 
5.3 
5.0 
3.9 
L0 
5. 00 
August 
4.0 
4.7 
5.9 
7.1 
5.2 
3.9 
8.2 
3.4 
5.4 
4.0 
0.2 
2.7 
6.7 
1.8 
4.51 
September 
9.2 
7.9 
6.6 
6.6 
5.7 
9.8 
2.3 
1.8 
1.8 
2.7 
4.8 
9.4 
5.7 
6.8 
5. 79 
October 
6.8 
10.2 
3.3 
5.5 
5.9 
8.1 
3.4 
4.9 
6. 9 
7.7 
9.5 
6.8 
5.8 
2.0 
6.20 
November 
8.3 
10.6 
5.5 
7.9 
4.9 
4.4 
6.8 
8.1 
11.9 
8.1 
15.7 
10.3 
12.0 
10.3 
8.91 
December 
28.2 
13.3 
22.0 
20.0 
25.8 
25.5 
20.9 
6.8 
10.0 
10.6 
15.9 
33.7 
8.2 
22.3 
18.80 
Year 
3.4 
6.7 
5.3 
8.2 
7.1 
fi.2 
3.0 
0.7 
3.6 
2.0 
LI 
3.7 
4.8 
4.21 
* This large variation indicates an evident error in the mean of this month for 1872. Omitting 1872, 
*he extreme variation is 4.3. 
