136 REPORT—1849. 
TABLE XXX. 
Mean electrical tension below 60 div. at each observation-hour in the three 
winters of 1845, 1846 and 1847, with the mean diurnal period of winter. 

div. | div. | div. | div. | div. div. div. | div. div. | div. | div. div. div. 
1845.) 20-1} 20°2| 19°8] 13:2| 29°6| 31°4 | 34:8] 34°8| 34:2] 31:7] 31°5| 29°2 | 281 
1846.) 29:2} 26°5| 24:2] 32°1| 32°5| 36°6 | 38:°3| 37°5| 38°8| 42:0] 43:4] 41°3 |° 33:8 
1847.) 23:°9| 22:7] 23°6 32°9 | 31°7| 36:8 | 38:0] 36°83] 37-1] 41:5] 39°4| 38-4 | 32:4 











Mean.| 24:5 | 23°2| 22°7 24-7 | 31-2] 35-0 | 37-1| 36:3] 36-6] 38-0| 37-7] 36-2 |-31°4 

TasLe XXXI.—Excess or defect of the mean electrical tension below 60 div. 
at each observation-hour, as compared with the mean of each winter in the 
years 1845, 1846 and 1847, and the mean of the three winters. 



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. 
1845. 8:0} 7:9 
1846.) 4°6| 7:3 
1847.) 8:5 | 9°7 
Mean.| 6°9| 8:2 



4a.M.10a.M. 10 P.M. 2A.M. In order to facilitate the compari- 
| son of the diurnal march of the low 
| tensions during the individual winters, 
which present some striking features 
of interest, we shall at once introduce 
the curves to the notice of the reader. 
On contemplating them, it will be at 
once apparent that they present se- 
veral interesting points of contrast. 
There appears to be a greater ap- 
proach to a single progression, espe- 
cially in the winter of 1845. In this 
curve the maximum occurs at noon 
and 2 p.M.; the precipitous diminu- 
tion between 10 p.m. and midnight 
disappears, the curve taking a gently 
rounded course from 2 p.m. to mid- 
night ; there appears to be a slight 
check to this gradual diminution of 
tension at 8p.m. The principal mi- 
nimum occurs at 6 A.M., the rise from 
this hour to noon being of a bold, 
rounded character ; it is probable that 
the true minimum occurs at 4 A.M., 
twelve observations only contributing 
to the determination of the value at 
6 a.m. On contrasting this curve 
with those of the summer and entire 
year aggregate tension, we find the 
movements during the day reversed, 
the greatest development occurring about the middle of the day. A much 

1845, Mean. 
1846, Mean. 
Fig. 8. 
1847. 
with the mean curve of the three winters. 
3 Winters. Mean. 
Mean diurnal curves of the electrical tension below 60 div. for the winters of 1845, 1846 and 1847, 
4A4.M, 10 4.M. 10 P.M, 2A4.M. 

