5(30 
ME. W. ELLTS ON MAGNETIC DIURNAL RANGE. 
of the small sun-spot irregularities of fig. 24 would therefore influence, in an insigni¬ 
ficant degree only, the forms of the corresponding upper and lower curves of figs. 8 
and 16 ; that is to say, the upper curves would still incline upwards at their middle 
points, and the lower curves downwards, indicating that after allowance is made for 
the accidental sun-spot irregularity (in the aggregate small), the magnitude of the 
diurnal range of declination and horizontal force at the time of a sun-spot maximum, 
as compared with the value at the time of a sun-spot minimum, is increased more in 
the summer than in the winter months ; or the annual inequality of magnetic diurnal 
range is increased at the time of a sun-spot maximum, and decreased at the time 
of a sun-spot minimum, as compared with the average annual inequality. In other 
words, the annual inequality appears to be increased when the mean diurnal range 
is increased, and diminished when the mean diurnal range is diminished. If it he 
desired to examine the question numerically, the materials for so doing may he found 
in Tables VII., VIII., and IX. ; hut, having exhibited the results in graphical form, 
it seems scarcely necessary here to pursue the subject further. 
The general conclusions which may he considered to be derived from the whole 
inquiry are— 
1. That the diurnal ranges of the magnetic elements of declination and horizontal 
force are subject to a periodical variation, the duration of which is equal to that of 
the known eleven year sun-spot period. 
2. That the epochs of minimum and maximum of magnetic and sun-spot effect are 
nearly coincident, the magnetic epochs on the whole occurring somewhat later than 
the corresponding sun-spot epochs. The variations of duration in different periods 
appear to be similar for both phenomena. 
3. That the occasional more sudden outbursts of magnetic and sun-spot energy, 
extending sometimes over periods of several months, appear to occur nearly simul¬ 
taneously, and progress collaterally. 
4. That it seems probable that the annual inequalities of magnetic diurnal range 
are subject also to periodical variation, being increased at the time of a sun-spot 
maximum, when the mean diurnal range is increased, and diminished at the time of a 
sun-spot minimum, when the mean diurnal range is diminished. 
Conclusions Nos. 1, 2, and 3 appear to be sufficiently certain, but the evidence in 
favour of N o. 4 is not so decisive. 
