INTERESTING FACTS CONCERNING THE SUN. 29 



often seen suspended at different heights in the solar atmosphere ; and frequently 

 the higher ones hide the lower from our view. 



Solar spots are principally seen on two zones parallel to the sun's equator, 

 one on each side of it, between lo" and 30° ot latitude. The rotation of the sun 

 was discovered by the displacement of these spots ; but it is remarkable that this 

 rotation is not similar on all points of the sun's surface. The angular speed is 

 greater at the equator, and diminishes as the degrees of latitude augment in num- 

 ber. The sun does not revolve according to the laws which we suppose to gov- 

 ern the movements of a solid body, whence it follows that we should regard it as 

 a mass of fluids. The sun's rotation is accomplished in a mean period of 25^3 

 days ; and we cannot as yet explain whether this rotation affects the solar atmos- 

 phere as well as the globe itself, for the interior regions are entirely hidden from 

 us ; but we can cite an indirect proof which has some importance, although it ap. 

 pears at first to be a little singular. 



Herr Hornstein, discussing the magnetic phenomena observed at Prague, 

 found in the movement of the magnetic needle a variation of which the period 

 was 26.33 days. On comparing it with certain data, he attributed the phenome- 

 non to the magnetic influence of the sun ; and if we admit that the magnetic 

 period above referred to is the same as that of the solar rotation, we find that the 

 sun turns on its axis in 24.55 days. Magnetic phenomena thus give us a new 

 idea of the period of solar rotation, which differs from that which we derived from 

 study of the whole solar surface, but which is similar to that formed on a study of 

 the sun's equatorial region. 



Some recent studies of solar spectra in connection with sun spots and other 

 features of the sun's envelope have led Mr. Charles S. Hastings, of the Johns 

 Hopkins University, to form a somewhat novel theory of the sun's constitution 

 and the conditions producing the more notable phenomena familiar to solar stu- 

 dents. 



Mr. Hastings finds, contrary to the received opinion, that the spectra of the 

 center and the outer edge of the sun's disk are not precisely alike, though the 

 differences are so minute as to escape all but the most perfect instruments and all 

 methods which do not place them in close juxtaposition. Certain of the Fraun- 

 hofer lines, the thickest and darkest in the spectrum, notably those of hydrogen, 

 magnesium and sodium, which appear with a haze on either side in the spectrum 

 of the center of the solar disk, are sharp and distinct in the spectrum of the limb. 

 Certain very fine lines are stronger at the limb, while other very fine lines are 

 stronger at the center. The ordinarily accepted theory of the solar constitution 

 and the origin of the Fraunhofer lines fails to explain these phenomena. The 

 probable reasons for this failure Mr. Hastings discusses at considerable length in 

 the January issue of the American Journal of Science, and then proceeds to frame 

 a theory of the sun's constitution, which, he thinks, will satisfactorily explain all 

 the observed phenomena. The limit of our space forbids more than the briefest 

 summary of his conclusions. 



