294 



NATURE 



\Attg. 8. 1872 



But is this rich composition common to all the protnberances, 

 or limited to a certain nnmljcr ? and do these materials extend 

 throughout tlie protuberance, or are they confined to a limited 

 portion of it? 



Tacchini's observations show that the varied composition in 

 question is limited to a very small height; in other words, to tin." 

 ntere base of tlie protuberance, whereas the higher portions ate 

 composed exclusively of hydrogen and the element D-j. Now, if 

 the protuberances were the result of violent eruptions, the sub- 

 stances ejected with sucli force could not fail to attain a consider- 

 able height above the base of the protuberance, which is contrary 

 to observation. Moreover, it is not all the protuberances that 

 give a mixed spectrum ; that is to say, they are not all formedjof 

 numerous materials, as they should be, at least in the majority 

 of cases if they were produced by violent eruptions. According 

 to Tacchini's observations, only 10 out of loo' protuberanc:'s 

 give a mixed spectrum, the remaining 90 giving spectra which 

 exhibit only the hydrogen lines and the line D.,. He also finds 

 that in all the spectra which he has observed, either of protubei- 

 ances near the sun's edge, or of clouds and filaments of greater 

 height, the hydrogen lines never occurred alone, but always ac- 

 companied by the line D.,. In one case only were the hydrogen 

 lines and D.j accompanied by other bright lines in the distinctly 

 higher portions of the protuberances. This was observed on 

 December 19, 1S71, on a magnificent pro'nberance resf'mbling a 

 great conflagration, the central part of which exhibited tA'O red 

 lines. 



If the jirotuberances were formed of materials violently ejected 

 from the interior of the sun, it would fc'Uow that at every point 

 of the sun's edge where a mixed spectrum occui's, that is to say, 

 where there is evidence of the presence of numerous materiah, 

 there also the corresponding protuberance should exist ; but ob- 

 servation .shows the contrary. 



From his first examination of the protuberance^, indeed, 

 Tacchini had been led to conclude that the bright protuberances 

 alone afforded certain indication of a rich variety of materials ; 

 but observing afterwards some parts of the sun's edge which, 

 though free from protuberances, nevertheless had a peculiar 

 structure, inasmuch as they were formed of a series of fl.imcs 

 higlier and brighter than usual, he was led to examine the spec- 

 trum of these portions more attentively ; and he found indeed 

 that there also, in addition to the lines of hydrogen and D^, lines 

 appeared corresponding to many other substances. A very 

 careful examination of the sun's edge was accordingly made in 

 August and September 1871, the result of which was to show 

 that in very extensive tracts of the edge, amounting to \ of the 

 whole, the entire chromosphere was invaded by the vapours of 

 various metals, although these same parts of the edge were not 

 covered by protuberances, an observation before made by 

 Lockyer. t 



These tracts continued to show themselves more or 

 less extensively for many days afterwards in the same 

 part of the sun's limb, representing in their aggregate vast 

 regions of the surface where the hydrogen of the 

 chromosphere was mixed = with many other substances 

 which commonly exist at the base of tire chromosphere. Thus 

 on the 2Sth of August and 17th of .September, 1S71, throughout 

 an area of 60°, from the position 30° to 90', the edge g.ive a 

 mixed spectrum, although the constituent substances were not 

 found to be present in the same number at all points of this arc ; 

 the greater number indeed were found at the middle of 

 the arc, while at the ends they were reduced to magnesium, 

 hydrogen and D.j of the chromosphere, so far as this last-men- 

 tioned line may be regarded as belonging to a peculiar substance. 

 This order in the number of substances on the portions of the 

 edge which give a mixed spectrum, has been observed so fre- 

 quently, that the regions of the sun corresponding to the aggre- 

 gate of these successive tracts may be regarded as isolated 

 portions of the solar surface, in the centre of which there is found 

 a large number of different substances, this number diminishing 

 towards the edge of each of these regions, where it reaches its 

 minimum ; and if we leave out of consider.ation the materials of 

 the chromosphere which are common to the whole surface of the 

 sun, we may say that at the borders of these regions there 

 remains nothing but magnesium. In these tracts or regions, 

 indeeJ, though the composition might be different in different 

 parts, magnesium was never absent ; for this reason Tacchini 

 designates these portions of the surface as iiunncsiuiii regions. 



Instead then of special points marked by eruptions, we find 



* T.accliini's observations divide prominences as Lockyer has divide i ihem. 

 t Proc. R.S. vol. xviii. p. 75 1S79 



on the sun's surface large regions exhibiting throughout a com- 

 plex spectrum, but not covered by protul^erances ; and this affords 

 the strongest argument for not regarding the protuberances as a 

 phenomenon of true eruption. We cannot therefore admit the 

 existence of a solid or highly resisting liquid stratum, but rather 

 a purely gaseous envelope, such as may permit of the ready 

 mixing of the internal materials with those of the chromosphere 

 on a vast scale, thereby giving rise to the regions above desig- 

 nated as regions of magnesium. 



This view, however, does not absolutely exclude the occur- 

 rence of eruptive phenomena ; for if these materials show them- 

 selves in the chromosphere at certain determinate pomts, they 

 must have issued or been ejected from the centre towards the 

 circumference. Tacchini, however, thinks that he has proved 

 that these eruptions are not violent, and do not take place 

 through a strongly resisting medium. 



Contempor.ineously with the determination of the angles 

 of position of the protuberances, and of the portions of the 

 chromosphere which exhibited a mixed spectrum, similar determi- 

 nations were made of the positions of the facula: and regions of 

 fr.cuhe visible or near the edge. A comparison of the two 

 series of determinations thus made showed the coincidence of 

 the magnesium regions with the regions of the facuhc. The 

 positions of the protuberances on the other hand did not 

 coincide with either. 



The limits of the regions of magnesium and of the faculx, on 

 either side of the sun's equator, were found to be as follows : — 



Regions of Magnesium, August 187 1 } _ 



J -f 60" 

 I - 32 

 S +43" 

 \ -32 

 i +64" 

 ( -32 



Considering now the magnesium regions above described, and 

 the intensity of the phenomena there exhibited, it is clear that 

 at any given epoch, the luminous intensity of the solar disc may 

 vary considerably, and exhibit great differences as compared with 

 that of the general envelope. At such times the solar atmo- 

 sphere will not be uniformly illuminated, but will include a 

 number of cones, varying in extent and brightness according to 

 the different magnesium regions existmg on the sun ; and Tacchini 

 suggests that in the case ol total eclipses of the son, during which 

 the solar atmosphere becomes visible to us in the form of an 

 aureola, this aureola which is differently illuminated in different 

 parts, and therefore presents the appearance of plumes perpen- 

 dicular or oblique to the edge of the moon, may arise fron the 

 cones embracing a large extent of surface corresponding to that 

 of the magnesium regions. 



Whilst 'Tacchini was studyingthe magnesium regions, Lorenzonl 

 obtained evidence that the temperature of the sun's surface is 

 least at the poles. The regions occupied by the metallic vapours 

 corresponding to a certain line, which probably belong to the 

 spectrum of iron, are called by Tacchini iron regions ; they do 

 not coincide with the regions of magnesium and of the facul;e, 

 or with those of the protuberances, which are more limited. 



Since the vapours of iron are diffused in the chromosphere on 

 so vast a scale, and the m.agnesium regions also are so large as 

 has been previously shown, Tacchini asks is it possible to admit the 

 existence of a state of solidity or viscosity in those envelopes, or 

 a temperature so low as some persons suppose ? He regards 

 such a view as totally inadmissible, and considers that all the 

 observations above detailed point to the conclusion that the time 

 is yet very distant when the sun will approach to those trans- 

 formations which have reduced the earth to its actual state ; and 

 that the sun is still an entirely gaseous mass, relatively hotter at 

 the centre, and cooler in the superficial strata, which we dis- 

 tinguish by the names of photosphere and chromosphere. 



September 



Regions of the Faculaa, August 



September 



ASTRONOMY 



On the Meteors of April 30-May 1* 



Prof. Schiai".\kelli, in his list of meteoiic showers whose 



radiant-points are derived from obser\ations made in Italy within 



the last few years, describes one as occurring on April 30 and 



May 1, the apparent position of whose radiant is in the Northern 



* From SWiimiHs Journal for July, 1S72. 



