324 DR. C. CHREE: ATMOSPHERIC ELECTRIC POTENTIAL RESULTS AT IvEW 
70 days into two groups, to the one of which each year contributes the five days in 
which P was greatest, while to the other it contributes the five days in which 
P was least. Table XIII. shows the excess of the mean P in the former group 
and of the corresponding mean values of certain meteorological elements as compared 
to the means from the second group. 
This second method gives notably larger differences of potential between the two 
groups, and so is more likely a priori to present decisive results than Table XII. In 
Table XIII. there seems in winter a very distinct association of high potential with 
low temperature and with low wind velocity. This is so far in accordance with 
Table XII. ; but the association of high potential with low temperature in Table XIII. 
extends to every month of the year except July, whereas in Table XII. March, May, 
August and September are exceptions to the rule. 
Table XIII.—Mean Excess of Values of Meteorological Elements for Groups of Days 
of Larger as compared to Groups of Days of Smaller Potential Gradient. 
Potential 
gradient. 
Barometric 
pressure in 
inches. 
Temperature, 
Fahrenheit. 
Wind, 
miles per hour. 
Sunshine, 
hours per day. 
January .... 
128 
+ 0-191 
o 
-5-09 
-3-33 
+ 0-40 
February .... 
109 
-0-009 
-5-99 
- 3-22 
+ 1- 26 
March . 
89 
+ 0-021 
-2-88 
- 1-40 
+ 1-26 
April . 
73 
+ 0-006 
-2-94 
- 2-62 
-0-59 
May . 
59 
+ 0-009 
-4-72 
+ 0-04 
-0-53 
June . 
52 
-0-009 
-1-40 
+ 2-07 
-0-26 
July . 
45 
+ 0-008 
+ 1- 94 
-0-26 
+ 2-65 
August . 
47 
-0-006 
-0-81 
-0-63 
+ 0-81 
September .... 
50 
-0-023 
-2-71 
+ 0-45 
+ 0-43 
October . 
81 
-0-058 * 
-3-28 
+ 1-11 
+ 0-91 
November .... 
115 
+ 0-109 
-5-49 
-2-13 
+ 0-79 
December .... 
130 
+ 0-054 
-6-22 
-0-64 
+ 0-05 
Year . 
81 
+ 0-024 
-3-30 
-0-88 
+ 0-60 
Winter . 
120 
+ 0-086 
-5-70 
-2-33 
+ 0-62 
Equinox .... 
73 
-0-014 
-2-95 
-.0-62 
+ 0-50 
Summer .... 
51 
o-ooo 
- 1-25 
+ 0-30 
+ 0-67 
Table XIII. shows also a greater apparent association of high potential with much 
sunshine than does Table XII. 
As regards barometric pressure, Table XIII. shows from April to August almost no 
trace of any association with potential gradient, and the results for the six months, 
September to February, in Tables XII. and XIII. differ in sign even. The results for 
barometric pressure are thus exceedingly contradictory. 
§ 20. The months which show a high mean value of P show also a large average 
daily range, but it by no means follows that the causes to which the two phenomena 
