with the extent of the Spots on the Sun. 259 
those of the sun-spot curve and that the auroral maximum is 
frequently more prolonged than the sun-spot maximum 
If we institute a comparison between the auroral curve and 
the magnetic curve we shall find the correspondence to be still 
more remarkable. The following table shows the dates of maxi- 
mum and minimum of these two classes of phenomena. Column 
third shows the difference between the dates in the first two 
columns. 
Date of Maximum. H Date of Minimum. 
pus nin al Auroras, M— A. | pet ser Auroras. M—A. 
1777 778 —10 1784 784 
1787 1787°5 0-5 1799°5 1798 +1°5 
1803 1804°5 —155 wanting 1811 
1817°5 1818 —0°5 1823°5 1823 +05 
29 1830 —1-0 wanting. 1834°5 
1838 1840 —2-0 1844 1843°5 +0°5 
1848°5 1850°5 —2°0 1856 1856 0-0 
18595 1859-5 0-0 1867 1867 0-0 
1870'5 1870°5 0-0 pine es te 
i - Z ths 
and America exhibits a true periodicity, following very closely 
the magnetic periods but not exactly copying them. In par- 
ticular we notice that during those periods in which the range 
of the magnetic declination was unusually small, as from 1794 
to 1824, auroral exhibitions were extremely few in number and 
insignificant in respect of brilliancy. é 
Ow we inquire as to the probable connection between 
these three classes of phenomena, we cannot suppose that a 
small black spot on the sun exerts any direct influence on the 
earth's magnetism or electricity, but we must rather conclude 
that the black spot is a result of a disturbance of the sun’s sur- 
face which is accompani an emanation of some influence 
from the sun, which is almost instantly felt upon the earth in 
an unusual disturbance of the earth’s magnetism, and a flow of 
electricity developing the auroral light in the upper regions of 
the earth’s atmosphere. The appearances favor the idea that 
this emanation consists of a direct flow of electricity from the 
sun. If we maintain that light and heat are the result of vibra- 
tions of a rare ether which fills all space, the analogy between 
