

ON ELECTRICAL OBSERVATIONS AT KEW. 
155 
notice here. The-progression is not single; it presents a depression at or 
near the period of the maximum, and an 
a 
= 
A. F, J. 
1845, 
years 1845, 1846 and 1847, with the 
1846. Mean, ak 
BS. 
8 
= Ba 
~ e3 
bp Be 
5 is 
<a oo 
3 Ea 
88 
Mean. 22 
1847. § 8 
a =] 
= 
ie] 
2 
oe 
2 
Ss 
S 
E 
5 
3 years. = ! Mean. 3g 
i=] 
g 
g 
Ay F, J. 3 
elevation at or near the period of the 
minimum. The maximum occurs 
in February and the minimum in 
August: commencing with the latter 
month, we have a gradual and un- 
interrupted rise until December of 
7°9 div.; this is succeeded by a de- 
pression of 1-4 div. in January, and 
in February the maximum occurs, 
showing an increase on January of 
2:2 div. The fall is then very gra- 
dual and uninterrupted until June— 
value 8:3 div. The elevation before 
spoken of occurs in July; it is as 
much as 3°4 div., and is succeeded 
by the minimum of August. The 
annual periods of single years par- 
take of the same irregularity of 
movement which characterizes the 
annual periods deduced from all the 
pasitive observations. 
The symmetrical position of the 
elevation and depression interrupting 
the general march of the electrical 
tension at July and January, and 
their coincidence with the usual 
turning-points of the annual curve 
of temperature, suggest the idea 
that they may be more or less con- 
nected with that curve; z.e. it is not 
improbable that they may be the 
turning-points of the annual curve 
which depicts the annual progression 
of atmospheric electricity as distinguished from that of aqueous vapour, the 
latter being more strongly developed and consequently overpowering the 
former. 
We have among the diurnal curves one that presents a striking similarity 
to that now under consideration; it is the curve of low tension for the mean 


Fig. 15. 
z | | | | Diurnal 
3 Winters. —- lang 
Low | i Annual 
tension. | Mean 
| 
of the three winters. In our ex- 
amination of this curve, we con- 
sidered that its peculiar form arose 
from the tendency in the readings 
to exhibit a single progression 
which was interrupted by the pre- 
sence of aqueous vapour affecting 
the lower readings. It will be ob- 
served that the two curves (fig. 15), 
although to a great extent possess- 
ing similarity of form, are strikingly 
in contrast; they are to a great extent the converse of each other. In the 
winter we find the lower tensions struggling to maintain a single progression, 
which is overpowered, not by the maximum being depressed, but by the 
superposition of two maxima in all probability the effects of aqueous vapour, 
