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lieliograph could easily be set at different points within these bands. 

 When the dispersion of the instrument was increased by means of 

 a grating, photographs of the Sun could be obtained with light falling 

 entirely within a widened line of hydrogen or of iron. 



Photographs made with Hs or Hy light showed also a flocky 

 structure, differing, however, materially from that obtained with H 

 and K. Hale and Ellermann therefore assume dark and bright clouds 

 of hydrogen to exist in the solar atmosphere. Upon the whole, but 

 not in the details, the hydrogen flocculi correspond in form and 

 position to the calcium flocculi photographed with H^ or K, light; 

 tlie general aspect of the photographs is fainter, the}^ show less 

 contrast, and the detailed structure obsei'ved in Hj or K^ light is 

 wanting. The most striking fact, however, is that the bright 

 c a 1 c i u ni f 1 o c e u 1 i o f t h e H, o r K, photo g r a p h s are 

 replaced o Ji the H 5 }) li t o g r a p h b y dark struc- 

 tures of similar for>n. Only in a few places in the vicinity 

 of sunspots small bright hydrogen flocculi occur which coincide 

 with parts of bright calcium flocculi. 



Hale and Ellerman hardly make an attempt to explain these facts 

 which, in the light of their working hypothesis, are really puzzling. 



We get a much clearer view of the matter as soon as we suppose 

 the widening of the hydrogen lines also to be produced by anomalous 

 dispersion, instead of by absorption only. 



Indeed, the ray-curving in the solar gases must generally be less 

 with waves belonging to those narrower dispersion bands than with 

 waves lying near the centres of the broad H and K bands. Even 

 in the powerful whirls of spot regions there will only sporadically 

 be found places where the tubular structure is sufficiently marked 

 to keep together rays belonging to the dispersion bands of hydrogen 

 in the same way, as it does gather the strongly curved Hj and Kj 

 light in the large, bright calcium flocculi. Accordingly, we shall 

 meet with very few places in bright calcium flocculi, where the 

 photographs in H5 or Hy light also exhibit brilliant points. All the 

 rest of the bright H^ and K^ regions correspond to those parts 

 of the gaseous mass where the differences of density — though not 

 so excessive — are nevertheless very considerable; but whereas in 

 that structure the Hg rays are repeatedly cur\ed and may be made 

 to converge, the less strongly incurvated H^g rays will in the same 

 regions diverge and be dissipated in a considerable degree, thus giving 

 rise to dark places in the photographs. Outside the bright calcium 

 flocculi, finally, where the H^ and K^ photographs are dark in con- 

 sequence of increased divergence of the beams, no strong incurvation 



