246 EF. Loomis—Comparison of Auroral Displays 
In comparing the relative extent of the black spots on the 
surface of the sun, | employ the relative numbers given by Dr. 
Rudolf Wolf of Zurich. While the correspondence between 
the fluctuations of the sun’s spotted surface, and the range of 
the magnetic declination is very remarkable; some small dis- 
erepancies are noticeable, particularly before the year 1825, when 
the observations were less numerous and systematic then they 
have since been; and it has appeared to me that these discre- 
pancies might be at least in part the result of the incomplete- 
ness and looseness of the observations themselves. In my 
former article already referred to, I pointed out certain years 
for which the relative numbers given by Dr. Wolf appeared to 
me to rest upon a very uncertain basis. These years were 
1793, 1794 and 1795; and also the years 1801 to 1807 in- 
increase his relative numbers for each of these years, by an 
average quantity equal to two-thirds of that which I had pro- 
sed, thus admitting the substantial justice of my criticism. 
t is also noticeable that the observations for the last month of 
1794 and the first two months of 1795, furnish very large rela- 
tive numbers, indicating an unusual activity upon the sun’s 
surface at that time; and this is a fact to which in my former 
article I desired to call special attention. 
For the years 1801-1807, the observations are very few and 
meager, and the comparison of Dr. Wolf's relative numbers 
with the range of the magnetic declination led me to think that 
his relative numbers were somewhat too large. Dr. Wolf's new 
discussion of the observations has led him to a slight increase 
instead of a diminution of his former numbers. The following 
statement will show how little weight is to be attached to these 
numbers. e year of supposed maximum in the extent 0 
the solar spots, is 1804. Now for the year 1802, Dr. Wolf has 
only eight observations from which he is able to deduce a value 
for his relative number; for 1803, he has but two observations; 
for 1804, but three ; for 1805, but one ; and for 1806, but jour 
observations. 
Now for the year 1870, in which he had himself carefully 
observed the solar spots on 276 days, and had received observa 
tions from other astronomers which informed him of the condi- 
tion of the sun’s surface on 352 days of the year, he obtained 
173°3 as the correct value of the ‘alata number ; or by a dif- 
