RANGE AND THE PERIOD OP SOLAR SPOT FREQUENCY. 
555 
sensible inequality (see the declination curve in 1857 and in other years, and the 
horizontal force curve about the year 1856, and also in other years), not to be explained 
by direct reference to the sun-spot curve. This suggests, as a matter for inquiry, the 
possible existence of variation in the annual inequalities. But the general examination 
of annual inequality is complicated by reason of the existence of the eleven year 
period. Thus in Table I. for declination the values for the successive months of 
January, in the years 1849 to 1851 (closely following a maximum epoch), are 9' , 0, 
8' - 0, and 6 /- 5 respectively, whilst in the years 1867 to 1870 (approaching a maximum 
epoch), the successive January values are 4 ,, 9, 5 /- 7, 6 /- 6, and 7 /# 4. The annual in¬ 
equalities have therefore been investigated near to the epochs of minimum and 
maximum only. Adopting the years 1843, 1856, and 1867 as epochs of minimum, 
and the years 1848, 1860, and 1870 as epochs of maximum, the means of the numbers 
in Table I. have been taken at each of these six epochs for periods of three years, both 
for declination and horizontal force, the middle year in each period being one of those 
just mentioned. Deducting from the numbers so found for each month, the monthly 
means for the whole period, 1841 to 1877 (the means of the numbers in Table I.), the 
annual inequality of each element at the different epochs, as referred to the mean 
annual inequality, is exhibited. The results for declination are contained in the 
following table, in which it is to be understood that the number under January 1843 
(6 /- 2) is the mean of the numbers for January (Table I.) in the three years 1842, 
1843, and 1844, and similarly throughout the table, the “mean” minimum and “'mean” 
maximum being in each case the mean of the numbers standing in the three columns 
immediately preceding. 
