i380 Researches on Solar Physics. 
telescope, and the appearance carefully mapped by the observer. 
(2.) Or we may call to our aid that art which has already prov 
of signal service in many branches of science, and, by means of 
photography, obtain autographs of our luminary, which we may 
measure and examine carefully at our leisure. 
Each of these has its advocates, but it is not our design to 
discuss the comparative merits of the two methods; on the con- 
trary, as each has its own special advantages, we are willing to 
adopt them both, and to avail ourselves of all those materials 
which our own observations or the kindness of friends may 
have put into our hands. 
$I. Historical sketch. 
8. The most important knowledge which we possess regard- 
ing the physical appearance and structure of our luminary is 
derived from the following sources. 
4, Sun’s rotation.—We are, in the first place, indebted to Gali- 
leo, if not for the first discovery of sun-spots, at least for the 
first attempt to ascertain through their means the period of ro- 
tation of our luminary. 
5. Nature of sun-spots—The next great advance in solar 
physics is due to Alexander Wilson, Professor of Astronomy at 
Glasgow, who in 1778, communicated a paper to the Royal So- 
ciety, describing certain phenomena with regard to spots, which, 
in his opinion and in that of many others, appear to indicate 
that spots are cavities in a luminous chatooeers which sur- 
rounds the sun. 
The accuracy of this conclusion has recently been questioned ; 
but whatever may be said regarding the theory, there can be 8 
doubt regarding the importance of the fact which was first re 
vealed by Wilson. 
6. Their periodicity—The next step is due to Hofrath Schwabe, 
of Dessau, who has shown, as the result of nearly forty years 
as a maximum about every ten years—a remark which led 
General Sabine to observe that the various epochs of maximum 
spot-frequency were also those of maximum magnetic disturb- 
ance in our own globe. 
7. Thei 
who has greatly extended our knowledge of this subject. In 8 
large and most remarkable work recently published, and con 
sun-spots have a proper motion of their own, those near the 
solar equator moving faster than those near the poles; and he 
has also ma¢le interesting remarks on the distribution of spots 
in solar latitude for different years. In addition to these new 
