ON ELECTRICAL OBSERVATIONS AT KEW. 137 
greater number of observations of high tensions contribute to the production 
of the aggregate curve in winter than in summer, and as a consequence, the 
observations on which the winter curve of low tension is based are less nu- 
merous than those on which the summer curve rests. In the curve now 
before us, the double progression niay be considered if not entirely, as almost 
disappearing ; the removal of the higher tensions appears to be accompanied 
by a removal of the forenoon and evening maxima, which is replaced by a 
maximum near the middle of the day. ‘This is extremely striking when we 
compare our curve with that of the winter, as deduced from all the positive 
readings (page 122); in this curve the forenoon and evening maxima are 
strongly developed, and the depression at 2 and 4 p.m. very distinctly marked. 
It would appear, on the supposition of the high readings being measures of 
the electrical tension of aqueous vapour, that in this particular winter (1845), 
very few measures of such tensions occurred below 60 div., so that in the 
great majority of instances, the readings below 60 div. were, more or less, 
measures of atmospheric electricity. The curve itself suggests the inquiry— 
Is the diurnal march of atmospheric electricity—viz. that which is uncombined 
with the electrical tension characterizing, or developed by, the presence of 
aqueous vapour—a single progression? In other words, does the electrical 
tension of dry air present a curve having simply an ascending and descending 
‘branch, the progression being in harmony with the temperature? We shall 
have occasion to refer again to this subject in a future part of this Report. 
On turning our attention to the winter of 1846, we find a curve more or 
less in harmony with those of the summer and entire year, and strikingly in 
contrast with that of the winter of 1845. It is however to be remarked, that 
the depression at 2 p.m. is but slight, and very much less than the depression 
during the summer of this year; the slight check which is apparent in the 
forenoon rise, at 8 A.M., tends to give the curve an appearance of possessing 
three maxima; there is indeed a great tendency to assume somewhat of the 
form of 1845, which appears to be counteracted by the greater development 
of the evening maximum. 
_ The winter curve of 1847 may be characterized as exhibiting considerable 
trepidation, and consisting of alternate but very subordinate maxima and 
minima, the principal of which occurs at 6 p.m. There is an evident ten- 
dency to a single progression, having its maximum about the early afternoon 
hours. This curve is in contrast with that of the winter of 1845, inasmuch 
as the most rounded portion of the curve is developed in the evening. 
On directing our attention to the mean of the three winters, we find two 
maxima, noon and evening, well-developed, but of a subdued character. The 
evening maximum is the principal; it however rises only 0:9 div. above that 
at noon; the intermediate minimum occurs at 2 P.m., and is depressed 1°7 div. 
below the principal maximum. 
uy TasLe XXXII. 
Synopsis of the principal points in the summer, winter, and yearly curves 
below 60 div. 
: Even. Max.|Aftern. Min. 
Forenoon |4,-_- Evening | Nocturnal 
Season. Maximum,| Minimum. Maxinium,| Mininvom,| . 22OVe below 
Forenoon. |Even. Max. 
‘ 7 div. div. 
4i1 Summer.} 10 a.m. Noon. 10pm. |2&4am. 41 5°6 
p Winter...| Noon. 2 p.m, 6p.m. 4a.m,. 0:9 17 
Year ....| 10 a.m. 2 p.m. 10 p.m. 4am. 3°2 3°5 

