128 



KNOWLEDGE, 



[June, 1903. 



iu position at least — with the " calcium facula> " photo- 

 graphed by Prof. Hale over the solar disc by meaus of a 

 double slit. The monochromatic photographs show that 

 these " calciuiu faculie " lie in a scries of belts also along 

 parallels of latitude. I have not heard whether a series of 

 such photographs — first taken by Prof. Hale towards the 

 beginning of the last maximum — have been made in any- 

 thing like a continuous manner during the decrease of solar 

 activity, and the minimum which has just passed. If so, 

 it would be interesting to know whether these bands move 

 or alter in amount as the solar activity decreases and 

 increases again. 



Eruptive prominences are exclusively found in the sun- 

 spot belts. Quiescent prominences have their maximum 

 within 15° of the poles when the sun is most disturbed, 

 and as his activity decreases they move downward and 

 crowd more or less closely round the equator. Since we 

 observe both only when on the sun"s limb, we cannot say 

 whether they are disposed in parallel belts or not. The 

 corona seems to follow closelv the law of distrilnition 



hot, but not luminous to any degree, its spots and lielts aie 

 distributed iu a marked manner along parallels of latitudes ; 

 and its rotation is accomplished once in about ten hours. 

 We are on the earth, a body with a solid crust, rotating 

 once iu 24 hours, and we can study the systems of electric 

 currents from which the earth's total magnetism chiefly 

 results. 



THE CHEMISTRY OF THE STARS. 



III.— STAES OF THE SECOND TYPE. 



By A. Fowler, f.k.a.s. 



Notwithstanding the great multitude of lines exhibited 

 by the spectra of stars of the second type, the task ot 

 investigating their chemical significance is iu some respects 

 easier, and often more certain in its results, than that 

 which has to be faced in dealing with stars of other types. 

 This is because of the very close resemblance between this 

 type of .star and the sun, so that whatever may be learned 



Fio. 7. — Pliotograpliic Spectrum of Aroturus, show! 



obeyed l\y the quiescent prominences, but its forms are 

 certainly greatly disturbed and modified by the presence 

 of eruptive prominences. Thus in the corona of 1901, 

 whilst the streamers on the western limb presented the 

 featureless symmetry of dead minimum, the streamers on 

 the eastern limb were moulded and distorted by under- 

 lying disturbances, strongly suggesting that the' type of 

 corona seen during any eclipse is not due so much to 

 the period reached in the cycle of solar activity as to 

 the actual disturbance of the sun at the very time.' 



But when the sun is actually quiescent then the undis- 

 turbed, we might almost say the normal, form of the 

 corona consists of two pairs of wings folded symmetrically 

 about and parallel to the sun's equator. So that it is 

 evident that the corona, 

 whether or not it 

 partakes of the sun's 

 motion round an axis, 

 is influenced by the 

 sun's rotation ; it owes 

 its form to this motion 

 when not disturbed by 

 other — for it more 

 powerful — influences. 



There are only three 

 liodies whose rotation 

 effects we can stndv. 

 The first is the sun, a 

 gaseous body, intensely 

 hot, and intenselv 

 luminous, rotating on 

 its axis once in 25 days ; 

 we can study the corona, 

 the calcium faculse and 

 the spots, all influenced 

 in a more or less marked 



; chemical origins of some of the i5rincipal lines. 



[Beproduced by kind permission of Sir Norman Lockyer.] 



from the spectrum of the sun by making use of more 

 powerful instruments than can be employed in the case of 

 stars, may be confidently assumed to be true of those stars 

 which resemble the sua in so far as their spectra can be 

 compared. 



Of the stars included in the second type, the two chief 

 varieties are typified by Areturus and Aldebaran ; or, 

 adopting the nomenclature of Lockyer, it may be said that 

 the second type comprises the Arcturian and Aldebarian 

 stars. In both varieties the same lines are present, but in 

 the Arcturian stars the hydrogen lines are relatively 

 stronger than in the Aldebarian, while the reverse is the 

 case with the other lines. On account of the predominance 

 of metallic lines in their spectra, both varieties are con- 



4.1 



H, Co 



Co 



8.— A small part of the 

 the principal 



degree by the sun's rotation. \\\- can study the planet 

 Jupiter, a body whose outer shell is probably liquid, still 



Spectrum of Areturus, showing chemical origins of some of 

 lines. (The scale indicates wave-lengths.) 



veniently grouped together by Lockyer as " icetallic 

 stars." Fig. 7, from a photograph taken at the Solar 



