118 REPORT—1849. 
TABLE V. 
Excess or defect of the mean electrical tension at each observation-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. div. div. div. div. div. | div. | div. div. -| div. 
+ 

——— | ————— |} ———— |} —_ | | | | 
—|-—|—-— | - +/+)/—]-—] +] +] + 
1845.|43°3 | 45°3 | 44°8 |34°5 | 16 | 21:3 | 4:8 | 3:2] 3° 8:0 | 35°8 | 54:1 | 63°1 
-|—-|—-|-/-| + })+4+/)+4+])+4+] +4) 4+)] + 
1846.|37°0 | 40°1 | 39°9 | 25°9 | 0-2 | 15-4 8:3 | 4:2 | 2°2 | 23:7 | 35-0 | 25°9 | 61:3 
—-|-}|-—|-/+/] + ]4+]4+] 4+] 4+ ]+].+ 
1847./52°6 | 55°2 |54°8 |37°6 | 2°4 | 26:2 {12:1 | 131 | 8:7 | 22°8 | 35°7 | 31:6 | 76:3 





~|-/;-/-| +] 4 +} +] 4 
Mean./44°3 46°8 | 46:4 | 32:7 | 1:3 | 21-2 85 | 4°6 | 2:2 |17-9 | 35:5 | 3771 | 66°9 
The above tables, which are based upon the numbers in Table II., clearly 
exhibit a double progression of the electrical tension during the twenty-four 
hours. The means of the first two years closely approximate, and in connexion 
with the general course of the numbers, give a proportional confidence, both 
with regard to the care manifested in making the observations and the faith- 
fulness of the record. The third year exhibits upon the whole a higher ten- 
sion, the means at midnight and 2 a.m. being the only values that are lower 
than those of the same hours in 1846. The mean of all the observations is 
66°9 divisions of Volta’s electrometer No. 1. 
There are only three exceptions to the general fact, that from 8 a.m. to 10 
p.M. the mean electrical tension is above the mean of the year. The mean 
diurnal period, as deduced from the three years, does not exhibit any depres- 
sion below the mean of all the observations between the above-mentioned 
hours. The hours that exhibit a depression below the mean are midnight, 
2, 4 and 6 a.m., and these are considerably in defect. The hour of mini- 
mum tension appears to be 2 A.M.,a gradual rise taking place from that hour 
until 6 a.m. Between the hours of 6 and 8 a.m. a rapid rise occurs, the 
tension being nearly doubled; it then increases gradually until 10 A.m., when 
a maximum is passed, after which it gradually declines until 4 P.m., the epoch 
of the divrnal minimum as contradistinguished from the zocturnal minimum. 
The tension then rapidly increases until 8 p.M., and at 10 P.M. passes another 
maximum rather considerably above the maximum of 10 a.m. From 10 p.m 
to midnight (two hours) the diminution of the tension is enormous, 814 
divisions of Volta No. 1. The midnight value is but slightly above the 
value at 2 A.M., the epoch of the minimum. 
The diurnal march of the tension is rendered more apparent to the eye by 
the annexed curves (fig. 2). The general similarity of the movements in the 
three years, and the close agreement between the curves of these years, and 
that of the mean diurnal curve as deduced from them, is, to a certain extent, 
satisfactory. The forenoon maximum is well marked in each case, as well 
as the evening maximum: in 1846 and 1847 this occurred at 8 p.M., and it 
may be probable that 9 p.m. may be the hour at which it is most frequently 
exhibited. 
The lower readings at midnight, 2, 4 and 6 a.m., demand particular atten- 
tion. From the note above extracted (see page 117), we find that tensions at 
these hours, above 50 div. of Volta No. 1, do not enter into the discussion. 
It is not only highly probable, but the absence of records at these hours, when 
Henley’s electrometer has ranged rather high, indicates that the conductor 

