RANGE AND THE PERIOD OP SOLAR SPOT FREQUENCY. 
559 
Considering the diagrams of Plate 24 firstly in regard to the forms of the magnetic 
curves (figs. 1 to 4 and 9 to 12), it is to be observed (figs. 4 and 12), that a tendency 
to greater activity is shown in spring and autumn than in summer, the tendency to 
decline of activity in summer being apparent in many of the separate curves (figs. 1 to 3 
and 9 to 11). It appears further that the curves show a tendency to separate more 
in summer than in winter, indicating variation in the annual inequalities, of periodic 
character; but in order to determine whether or no they possess this quality, we 
must consider and estimate the possible influence'” of the corresponding sun-spot 
irregularities (figs. 17 to 20). Comparing these with the magnetic curves, it may be 
remarked that the unusual rise in the upper curves of figs. 3 and 11 seems (according 
to what was seen in Plate 23) to be in great part due to the corresponding sun-spot 
activity shown in the upper curve of fig. 19. It is therefore conceivable that, con¬ 
versely, the upper curves of figs. 1 and 9 would have ranged higher but for the sun¬ 
spot influence indicated by the corresponding upper curve of fig. 17. These points 
are, however, somewhat better indicated in the supplementary curves (figs. 5 to 7, 
13 to 15, and 21 to 23), which show the deviation from the mean annual curve (the 
middle curves of figs. 4, 12, and 20) in each period for each element.! Thus the 
influence indicated by the upper curve of fig. 23 is seen in the corresponding upper 
curves of figs. 7 and 15 ; the converse influence indicated by the upper curve of 
fig. 21 having probably operated to lower the middle portions of the corresponding 
upper curves of figs. 5 and 13. If on making allowance in this way for the 
accidental sun-spot influences, the upper curves (figs. 5 to 7, and 13 to 15) appear 
to bend upwards at their middle points, and the lower curves downwards ; we have 
indication that the variation in the annual inequalities of the magnetic elements is 
really periodic. There is a general accordance in this respect as regards declination, 
but the agreement for horizontal force is not so good, the lower curve of fig. 13 and 
the upper curve of fig. 14 being both contradictory. The mean effect is exhibited in 
figs. 8, 16, and 24. The upper curves of figs, 8 and 16 clearly bend upwards, and 
the lower curves downwards, and the question now is how far these indications are 
likely to be modified by consideration of the corresponding sun-spot indications of 
fig. 24. It is to be remarked that the sun-spot scale was so arranged with regard to 
the magnetic scales that corresponding motions (see Plates 22 and 23) occupy vertical 
spaces on the paper of about equal magnitude, and the same relative scale is employed 
in Plate 24. If anything, the sun-spot scale is somewhat too large. Consideration 
* Although, for brevity, it is convenient here and in following sentences to speak of sun-spot influence, 
the sun-spot phenomena are probably only incomplete manifestations of solar or cosmical action as yet 
only imperfectly understood. 
t The middle curve of fig. 20 represents the average annual inequality or irregularity of sun-spot 
frequency; and, unlike the corresponding magnetic inequalities (see middle curve figs. 4 and 12), it 
is nearly a straight line, which explains how reference to it produces so little change in the form of the 
curves, figs. 21 to 24, as compared with those of figs. 17 to 20. 
4 C 2 
