with the extent of the Spots on the Sun. 257 
_ The average number of auroras for each period of three 
years has been projected upon the accompanying chart, Plate 
I, which accordingly shows the fluctuations in the frequency 
of auroras for a period of 96 years. This auroral curve shows 
great irregularities in the number of auroral exhibitions, but 
affords unmistakable evidence of a periodic alternation of 
Date of Maximum. l| Date of Minimum. 
Solar Spots. peut Pinu. S— M. | Solar Spots. yea toad S—M. 
1778 1I77 +10 1784 1784 0 
1788.5 1787 +1°5 1798 1799°5 —1: 
804 1803 +1:0 1810 wanting. | unknown. 
1816.5 1817.5 —1°0 823 1823°5 —O0°5 
1829.5 1829 +0°5 3°5 wanting. | unknown 
1837 838 —1'0 1843°5 1844 —05 
1848.5 1848.5 0 1856 1856 0 
1860 1859.5 +0°5 1867 1867 0 
__1870 | 18705 | —05 ice ida i 
presume that a portion of the discrepancy in the undulations of 
the two curves is due to the imperfection of the earlier observa- 
ions. comparison of these observations seems to justify 
the following conclusions contained in my former article (this 
ournal, vol. 50, p. 160 F sees 
1. A diurnal inequality of the magnetic declination, amount- 
ing at Prague to about six minutes, 1s independent of the 
changes in the sun’s surface from year to year. , 
