IN THE MEAN EFFECTS OF THE LARGER MAGNETIC DISTURBANCES. 119 
diurnal variation on the hours of local time, but with different hours of maxima and 
minima ; it has also shown, generally, that there is an influence connected with the 
period of the year on the frequency of occurrence of the disturbances of principal 
magnitude, affecting the aggregate effects of the disturbing causes ; but it has not 
yet succeeded in tracing a definite epoch of semiannual change in the disturbances 
with the same precision as in the diurnal variation, of which the phenomena have 
been so much longer and so much more minutely studied, and in which the epoch of 
change in the phase depending on the earth’s revolution in its orbit has been distinctly 
traced to the very days of the equinoxes* 
The progressive augmentation of the range of the diurnal variation between 1843 
and 1848, is quite as conspicuous in the respective winters at Toronto and Hobarton 
as in their summers : the ratio of the increment of the range is even somewhat greater 
in winter than in summer. This has an important bearing when we regard the 
diurnal variation as divided into two portions, one depending on the earth’s revolu- 
tion on its axis, and the other on the earth’s revolution in its orbit. 
The extreme range of the periodical inequality of the diurnal variation from 1843 
to 1848, f. e. the difference between the ranges of the diurnal variation in 1843 and 
1848, is less at Toronto and Hobarton than the difference in the mean winter and 
summer ranges in any single year, i. e. than the inequality due to the position of the 
sun with reference to the equator. 
That the progressive increase in the mean monthly diurnal range from 1843 to 
1848, was not confined at Toronto and Hobarton to the Declination only, but took 
place likewise in the diurnal variations of the Inclination and Total Force, is shown 
in the subjoined Tables XVIII. and XIX., XX. and XXI., which appear to require 
no further explanation, as they are arranged on the same plan as Tables XV. and 
XVI. 
Table XVIII. — Mean monthly diurnal range of the Inclination at Toronto. 
Years. 
Winter. 
Spring and Autumn. 
Summer. 
Mean in the 
whole year. 
November, December, 
January, February. 
March, April, 
September, October. 
May, June, 
July, August. 
1843 
1*26 
i-40 
i-50 
1-39 
1844 
0-78 
1-39 
1-59 
1*25 
1845 
0-88 
1-33 
1-57 
1-27 
1846 
1-09 
1-59 
1-92 
1-53 
1847 
1-43 
2-22 
1-98 
1-88 
1848 
1-73 
2-17 
2-18 
2-03 j 
* Magnetical and Meteorological Observations at the Cape of Good Hope, vol. i. p. 15, &c. ; and at Toronto, 
vol. ii. Plate II. figs. 6 and 7. 
