FROM SELECTED DAYS DURING THE SEVEN YEARS 1898 TO 1904 
323 
Table XII.—Mean Excess of Values of Meteorological Elements for Group of Years 
of Larger as compared to Group of Smaller Potential Gradient from s (selected 
days) and a (all days of month). 
1 
1 
Potential 
gradient. 
Barometric pressure, 
in inches. 
Temperature, 
Fahrenheit. 
Wind, 
miles per hour. 
Sunshine, 
hours per day. 
s. 
a. 
s. 
a. 
s. 
a. 
s. 
a. 
January . 
67 
-0-061 
-0-058 
- 1-1 
- 1-1 
+ 0-1 
+ 1-2 
-0-15 
+ 0-10 
February . 
73 
+ 0-015 
+ 0-064 
-0-9 
-2-5 
- 1-2 
-3-0 
-0-32 
-0-03 
March . 
40 
+ 0-023 
+ 0-042 
+ 1-1 
+ 0-8 
+ 2-1 
+ 0-8 
+ 1-61 
+ 1-01 
April . . 
34 
-0-059 
+ 0-033 
-3-3 
- 0-6 
+ 4-5 
+ 1-2 
- 1-58 
-0-61 
May 
49 
+ 0-076 
+ 0-057 
+ 0-4 
+ 2-0 
-0-3 
-o-i 
+ 2-32 
+ 0-99 
June . . 
31 
+ 0-031 
-0-014 
-0-4 
- 1-3 
+ 1-3 
+ 0-1 
+ 0-59 
+ 0-04 
July • - 
20 
o-ooo 
0-000 
- 2-0 
- 1-9 
+ 1-3 
+ 0-7 
-0-27 
- 0-88 
August. 
22 
- 0-021 
+ 0•005 
+ 2-5 
+ 2-0 
+ 2-7 
+ 2-0 
+ 0-34 
+ 0-76 
September. 
37 
+ 0-037 
+ 0-071 
+ 2-2 
+ 0-4 
+ 0-1 
+ 0-6 
+ 1-36 
+ 0-70 
October 
40 
+ 0-041 
+ 0-015 
- 1-8 
-0-4 
-2-4 
-1-5 
-0-31 
-0-17 
November. 
72 
-0-016 
+ 0-062 
- 1-7 
-3-2 
-2-7 
-1-5 
+ 0-13 
+ 0-13 
December . 
84 
-0-146 
-0-047 
-1-9 
- 1-4 
- 2-0 
-1-7 
-0-39 
-0-44 
Year . . 
47 
-0-006 
+ 0-019 
-0-58 
-0-60 
+ 0-29 
- 0-10 
+ 0-28 
+ 0-13 
Winter. 
74 
-0-052 
+ 0-005 
-1-40 
-2-05 
- 1-45 
- 1-25 
-0-18 
-0-06 
Equinox . 
38 
+ 0-011 
+ 0-040 
-0-45 
+ 0-05 
+ 1-08 
+ 0-28 
+ 0-27 
+ 0-23 
Summer . 
30 
+ 0-022 
+ 0-012 
+ 0*12 
+ 0-20 
+ 1-25 
+ 0-68 
+ 0-74 
+ 0-23 
The difference between the mean values of P for the two groups is considerably 
larger in winter than in summer, but in every case it represents a very appreciable 
fraction of the mean from the whole 7 years. As a rule, the meteorological results 
have the same sign whether we take all the days of the month or the selected 
days only. 
In the four summer months there seems an association of high potential with high 
barometer, high temperature, high wind velocity and much sunshine; but the 
association with temperature in particular is very doubtful, two months going one 
way and two the other. Equinox agrees on the whole with summer, but the 
association is less clear. In winter the results seem the exact opposite of those iii 
summer, but the association with sunshine is small and uncertain. 
The association of high potential with low temperature in winter is the most 
consistent. It will be remembered that the selected days in winter show a markedly 
lower temperature and less wind velocity than the average day of the month, and 
these meteorological conditions, as we now see from Table XII., appear to be associated 
at that season with large values of P. 
§ 19. The second method adopted was to split the ten selected days in each 
individual month into two groups of 5, the one containing the days of highest mean P, 
the other those of lowest mean P. In the case of March, for instance, we thus split 
2 t 2 
