E. Loomis on Solar Spots, Magnetic Declination, etc. 167 
Magnetic storms compared with the prevalence of solar spots. 
Since the mean daily range of the magnetic needle is great- 
est on those years in which the sun’s surface is most disturbed, 
we could not be surprised if the range of the magnetic needle 
should prove to be the greatest on those days on which the so- 
lar spots are most extensive. In order to test this question, I 
have compared the extent of the solar spots for 6 days preced- 
ing and 6 days following each of the great magnetic disturban- 
ces at Greenwich for a period of 23 years. In the Greenwich 
observations for 1862 is given an abstract of the magnetic ob- 
servations on 177 days of great magnetic disturbance from 1841 
to 1857; and in the observations for 1867 are enumerated the 
days of great magnetic disturbance from 1858 to 1863, amount- 
ing in number to 45. These 23 years furnish 222 days of great 
disturbance, and I have compared Wolf's numbers represent- 
ing the extent of the solar spots near the time of these dates. 
Having prepared a table with 13 vertical columns, I insert in 
the middle column, Wolf's relative number for one of the days 
of great magnetic disturbance, and I also insert in their appro- 
. . re 
hose cases in which very few observations of the solar spots 
were made, and a few cases in which there were two or three 
have generally selected the day of greatest disturbance and 
tabl 
cases of 
disturbance which I have thus employed amount to 185. The 
before the storm, and also 1, 2, 3, etc., days after the storm. The 
horizontal lines indicate the amount of disturbance of the sun’s 
surface as measured by Wolf's relative numbers extending 
from 45 to 58. From this curve it will be seen that the dis- 
turbances of the sun’s surface about the time of a magnetic 
storm, bear an analogy to the waves in our own atmosphere 
about the period of a violent winter storm. We find a well- 
