150 REPORT—1849. 
In addition to the principal results of the discussion of the aggregate and 
low tensions on pages 138 and 141, we find from that of the high, that the 
’ movements of the electrical tension above 60 div. in the winter are such as 
strongly to confirm the suggestion of the forenoon and evening maxima re- 
sulting from such high tensions. 
Tables XLIX., L. and LI. exhibit the mean electrical tension above 60 div. 
at each observation-hour for each month in the three years 1845, 1846 and 
1847, with the monthly, seasonal and yearly means.—The characters of the 
monthly movements are exhibited to the eye in the sheets of curves illus- 
trating this report. See Plate X. and XI. 
Table LII. exhibits the mean monthly electrical tension at each obser- 
vation-hour, deduced from the observations of three months; also the mean 
summer, winter and yearly tensions, deduced from the observations of three 
summers, winters and years. The last line in the table, to which the word 
« Means ” is prefixed, exhibits the mean tension in each month, as deduced 
from all the separate monthly observations ; 7.e. the mean tension of January, 
277'1 div., is the result of all the January observations in the three years. 
The same thing holds good of the seasonal and yearly mean tensions. 
The curves projected from these numbers will be found on Plate XI. 
ANNUAL PERIOD. 
Aggregate observations.—One of the principal results of the foregoing dis- 
cussion has been to exhibit the march of the electrical tension during the twenty- 
four hours constituting the period of a day. This march has been found to 
present two well-defined maxima, in most instances removed from each other 
by an interval of twelve hours, the principal occurring at 10 p.m. and the in- 
ferior at 10 A.m. Two minima have also been ascertained, the principal at 
4 A.M, and the subordinate at 4 p.m. Ata particular season of the year, 
there have been indications of a curve of low tension presenting considerable 
approximation to a single progression, more or less in harmony with the curve 
of temperature; but the curve deduced from all the positive observations is 
not in harmony with the curve of temperature, inasmuch as neither of the 
maxima corresponds with either of its turning-points. We must not however 
forget, that the greatest development of electricity, so far as the diurnal 
period is concerned, takes place from sunrise to 10 P.M., and includes the 
period that the sun is above the horizon, and to this extent there is a con- 
nection between the temperature and the electrical tension. We now pro- 
ceed to examine those changes of the electrical tension, the period of which 
is completed in the same time that the earth is occupied in making a revolu- 
tion round the sun. 
The following table contains the number of readings in each month of the 
three years which form the bases on which the results in the succeeding 
tables rest. It will be remarked, that the greatest number occur in the sum- 
mer and the least in winter, the cause of which has been already referred to 
as resulting from the cessation of observations at 6 a.m. during the winter 
months, 

