RANGE AND THE PERIOD OF SOLAR SPOT FREQUENCY. 
551 
(so far as examination of the sun-spot numbers shows) has, as might be expected, no 
corresponding annual period.* The numbers in Table VI. do indeed yield a small 
inequality of irregular character (see the means at the foot of the table), but it is, if 
not wholly accidental, of very small magnitude as compared with the general changes 
shown by the sun-spot numbers, and is not further considered here. The magnetic 
diurnal ranges must therefore be now treated in such a way as shall eliminate their 
average annual inequalities without destroying or reducing their other fluctuations 
which are the proper subject of comparison with the fluctuations of the sun-spot 
numbers. To proceed now with a description of the process used. We have at the 
foot of Table I. the means of the whole of the values standing in each vertical column 
of the table ; also the general mean both for declination and horizontal force. And it 
will be seen, in the case of either element, that the differences between the general 
mean and the several mean monthly values give corrections, applicable severally to 
all the numbers in each of the twelve columns of the table. The corrections to the 
declination values of Table I. so found are, for each month respectively, as follow : 
For January +2 /, 7, February J-l'A, March —0' - 8, April — 2 r, 5, May — 1 /- 6, June 
—1 /- 7, July —1''3, August —l'*9, September —0''8, October -f-0'‘4, November + 2''4, 
and December -f-3 ,- 7. The corresponding corrections to the horizontal force values of 
Table I. for each month respectively are : For January +7, February +6, March + I, 
April —7, May —6, June —6, July —6, August —4, September —2, October -f 1, 
November +7, and December +9. By application of these series of corrections to 
the values of Table I. the average annual inequality of each element is removed, 
whilst the accidental variations remain. The numbers found in the way described are 
given in the next table. 
* The annual inequality of magnetic diurnal range varies with locality. For instance, at Hobarton, in 
latitude 43° south, the annual inequalities, as compared with Greenwich, are reversed, the diurnal ranges 
being greatest in our winter, and least in our summer. The sun-spot variation, an independent cosmical 
phenomenon, can have no relation with the constant part of the annual inequality which depends on local 
geographical position. 
4 B 2 
