SOLAE VORTICES AND MAGNETISM IN SUN SPOTS. 



[With 5 plates.] 



By C. G. Abbot. 

 Director, f>mitJison.iait, Astrophijfiifal Ohiicrvatory. 



At the present time the growth of knowledge of the sun is mainly 

 through the applications of the spectroscope, although in the past 

 information of great value was obtained by purely telescopic obser- 

 vations. Thereby the rotation of the sun was first measured, and the 

 remarkable retardation of the rotation with increasing distance from 

 the solar equator was established. Furthermore, it was discovered 

 that the prevalence of sun spots waxes and wanes in periods wdiicli 

 average about eleven years, although individual sun-spot cycles 

 range from eight to fourteen years in length. By utilizing with the 

 greatest art the rare instants of good seeing, Langley made his cele- 

 brated and beautiful drawings of the detailed structure within and 

 around a typical sun spot. Similarly, by the selection of specially 

 favorable conditions, Janssen was able to obtain photographs which 

 show, as well as may be, the granular appearance of the general sur- 

 face of the Sim. Owing to the fortunate circumstance that the moon 

 sometimes covers the body of the sun, leaving the surroundings open 

 to view undimmecl by the glare of the skylight, the beautiful struc- 

 ture of the corona and prominences became known from eclipse 

 observations. Comparative studies of successive eclipses prove these 

 features to be variable in high degree. The changes seen in the sun 

 sjDots, prominences, and corona made it clear that very great rear- 

 rangements of the material of the sun go on continually; but if it 

 were not for the aid of the spectroscope, knowledge of the character 

 of these changes would probably forever be very meager. 



Looking toward the sun we see through a layer of solar material, 

 which, if we neglect the corona, may be several thousand miles deep. 

 In this layer are contained the vapors of many of the elements found 

 on the earth, notably of sodium, calciinn, magnesium, iron, titanium, 

 vanadium, chromium, and others, besides several of the permanent 

 gases, like hydrogen and helium. Owing probably to the differing 

 densities of these elements, and in a rough way connecting itself with 

 their atomic weights, their distribution in level is not a homogeneous 



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