" ON ELECTRICAL OBSERVATIONS AT KEW. 131 
TasLeE XXII. 
Excess or defect of the mean electrical tension below 60 div. at each obser- 
vation-hour, as compared with the mean of the year for the three years 
1845, 1846 and 1847, and the mean diurnal period. 








Year.| Mid. |2 a.m.|4 a.m.|6 a.m.|8 a.m.|10 a.m.{Noon. 2 p.m.|4 p.m.|6 p.m./8 p.m.|10 p.m.|Mean. 
div. | div. div. | div diy. ‘ div. div. "4 div. y div. | div. z div. div. div. [ 
pee (a | eS = AG ate stele chem (eats | ste (eats oe 
1845.)6°1 | 81) 84 5 | 07 2°8 3°8 | 55 | 46] 46] 5:7 4:9 | 25:99 
. ~}-|/-;/-/;+/4+]/+]+]+]+/+#] + 
11846.) 4:5 | 7:6) 78} 38] 1:7 | 36 | 25) 1:7) 32] 5:5] 62] 7:2 | 28:8 
= ies aa a a5 ae aid agace dlegs ay eae Gia ae 
1847.) 7°4 |10°0 |10'2 | 4:0 | 1:0 4:9 44) 28] 39 | 64) 69 81 | 311 




-}/-/-];|-/+]/+/+]+/+ ]+ 
Mean.|6°0 | 85 | 87] 49 | 10] 3:7 | 36) 3:4) 39 | 55 | 62) 69 | 28°6 


In the above tables the double progression, so apparent in the curves de- 
duced from all the positive observations, is but slightly developed. The fore- 
noon maximum at 10 a.m. rises very slightly above the afternoon minimum 
at 2 p.M.—only 0°3 div. The evening and principal maximum occurs at 10P.M., 
presenting the highest mean reading of the series. The year 1847 is marked 
by an increase in the low as well as in the aggregate tension, this increase 
appearing after the hour of 4 a.m. If the separation of the high from the 
low tensions at the point of 60 div. be that which is most accordant with 
truth, and the above tables exhibit more accurately the movements during 
serene weather than those which form the preceding part of this discussion, 
it would appear that upon contemplating the movements as deduced from the 
three years, there exists a great tendency to soften down or even to obliterate 
the forenoon maximum in such movements, so as to exhibit an approach to 
a single progression. The departure from an exhibition of the érwe march of 
the electricity of serene weather by the numbers before us, has been alluded 
to, inasmuch as the same cause, viz. the presence of aqueous vapour, must 
influence the results as deduced from the lower as well as those from the 
higher readings, and it becomes a curious matter of inquiry as to how far 
both the subdued maximum of the forenoon and the more decidedly deve- 
loped maximum of the evening, in the progression of the lower tension, may 
be due to the presence of such vapour. It is a matter worthy of remark, and 
‘certainly is not without great signification, that the curves already discussed 
agree in presenting a precipitous downward movement between 10 p.m. and 
midnight. The tables now under consideration present in avery decided manner 
the same feature: although the extent of the diminution of tension is not so 
great as in the aggregate curves, yet as compared with the other two-hourly 
_ movements, it is sufficiently large to constitute a marked contrast to them, 
and this is by no means to be confined to the tensions we have hitherto ex- 
amined ; it will be found as we proceed to be an invariable accompaniment 
to nearly the whole of the curves. 
_ The mean of the 7529 observations below 60 div. is 28°6 div., or 38*3 div. 
‘Tower than the mean of the 10,176 positive observations. The minimum 
_ occurs at 4 a.m., from which hour the tension gradually rises until 10 a.m.; 
avery slight depression of 0-3 div. then takes place, the turning-point being 
at 2 p.M., from which hour the rise is very gradual until 10 p.m., the prin- 
" Cipal maximum, which is immediately succeeded by the precipitous diminu- 
; KZ 

