—— : 
AMERICAN 
JOURNAL OF SCIENCE AND ARTS. 
[SECOND SERIES.] 
Art. XVL—Comparison of the mean daily range of the Magnetic 
Declination, with the number of Auroras observed each year, and 
the et of the black Spots on the surface of the Sun ; by ELIAs 
Loo 8, Professor of Natural Philosophy in Yale Coll ege. 
In 1826, M. Siiteabe of Dessau in Germany commenced a 
series of observations of the nae spots which he has continued 
to the present time. For each year he has kept a record ofthe 
number of ri of observation, the number of groups of spots 
“anal g and the lays on which the sun was om spots. 
These observations decidedly indicate a oe in the num- 
ber of the solar spots, a maximum recurring at an interval of 
from 7 to 13 years. In 1849, Dr. Rudolf Wolf, of Zurich, 
Sipinailatsd commenced a series of observations for the same 
object as those of Schwabe, but upon a plan somewhat more 
precise “aii thorough. Bee each day of ote gation: he recorded 
two numbers; the first showed how many groups or isolated 
poe were seen with a ps feet Fraunhofer telescope and a 
power of 64; the second showed the total number 
of visible aad for that day. In order to deduce from these 
observations a series of numbers which shall be ge 2 daar 
to the amount of spotted surface of the sun, he multiplies 
the number of gronps for each day by ten, and sida to this 
cig the total nunber of spots. Thus, if on a certain day 
counts 9 groups and 31 single spots, he obtains 121 
(9. x 10431) which he calls the relative number. The mean of all 
the numbers thus obtained for a month, is the relative number 
for that month ; and the mean of the number thus obtained for 
Am. Jour. Sor.—-Sadox Series, Vou. L, No. 149.—Supr., 1870. 
10 
