1853] 



PHYSICAL CONSTITUTION OF THE SUN. 



dicated concerning the constitution of the solar photosphere. 

 These results, let it be loudly proclaimed, are entirely due to the 

 united efforts of the observers of the 1 7th and 18th centuries, 

 and also in a certain measure to those of our contemporary as- 

 tromomers. And, here, let me make a remark, which, when 

 endeavouring to determine the physical constitution of the stars, 

 we shall have occasion. to apply. If the material of the solar 

 photosphere were liquid, if the rays emitted from its margin were 

 polarized, the two images furnished by the polarizing telescope 

 would not only be colored, but they would be different in different 

 parts of the circumference. Is the highest point of one of these 

 images red, the point diametrically opposite will be red also. But 

 the two extremities of the horizontal diameter will each exhibit a 

 green tint and so on. If then, one succeeds in concentrating to 

 a single point, the rays emitted from all parts of the sun's limb, 

 even after their decomposition in the polarizing telescope, the mix- 

 ture will be white. 



The constitution of the sun, as I have just established it, may 

 equally serve to explain how, on the surface of the orb, there 

 exist some spots not black but luminous. These have been called 

 facuta, others of much smaller dimensions, and generally round 

 have been called lucules. These latter cause the surface of the 

 sun to appear spotted. It is a singular fact ; but I 

 may trace the origin of the discovery of the faeulre and lucules 

 to an administrative visit to a shop of novelties, on the Boule- 

 vards. " I have to complain," said the master of the establish- 

 ment, " of the Gas Company; it ought to direct on my goods 

 the broad side of the bat wing burner, whilst, by the carelessness 

 of their servants, it is often the edge which is directed on them." 

 " Are you certain," said one of the assistants, " that in that posi- 

 tion the frame gives less light than in the other?" The idea, ap- 

 pearing ill-founded, and I would say, absurd, it was submitted 

 to accurate experiment; it was determined that flame sheds upon 

 any object as much light when it illuminates by its edge as when 

 its broad surface was presented to it. Thence resulted the con- 

 clusion, that a gaseous incandescent surface of a determined ex- 

 tent is more luminous when seen obliquely than under a perpen- 

 dicular incidence. Consequently, if like our atmosphere, wdien 

 dappled with clouds, the solar surface presents undulations, the 

 parts of these undulations which are presented perpendicularly 

 to the observer, must appear comparatively dim, and the inclined 

 portion must appear more brilliant ; and hence every conic cavity 

 must appear a lucule. It is no longer necessary in accounting 

 for these appearances, to suppose that there exists on the sun 

 millions of fires more incandescent than the rest of the disc, or 

 Millions of points distinguishing themselves from the neighbor- 

 ing regions by a greater accumulation of luminous matter. 



After having proved that the sun is composed of a dark cen- 

 tral body, of a cloudy-reflecting atmosphere, and of a photosphere 

 we should naturally ask if there is nothing besides. If the pho- 

 tosphere terminate abruptly and without being surrounded by a 

 gaseous atmosphere, less luminous in itself, or feebly refracting? 

 Generally, this third atmosphere would disappear in the ocean of 

 light, with which the sun always appears surrounded, and which 

 proceeds from the reflection of its own rays upon the particles of 

 which the terrestial atmosphere is composed. A means of re- 

 moving this doubt presented itself; it was selecting the moment, 

 when, during a total eclipse, the moon completely obscures the 

 sun. Almost at the moment when the last rays emanating from 

 the margin of the radiant orb, disappeared under the opaque 

 screen formed by the moon, the atmosphere in the region, which 

 is projected between the moon, the earth, and the neighbouring 

 parts, ceased to be illuminated. In all our researches upon solar 

 eclipses, innumerable unexpected appearances invariably present 

 themselves; the observers were not a little surprised, when, after 



the disappearance of the last direct rays of the sun behind the 

 the margin of the moon, and after the light reflected by the sur- 

 rounding terrestrial atmosphere had also disappeared, to see rose- 

 shaped prominences from two to three minutes in height, dart, 

 as were, from the circumference of our satellite. Each astrono- 

 mer, following the usual bent of his ideas, arrived at an indepen- 

 dent opinion regarding the causes of these appearances. Some 

 attributed them to the mountains of the moon ; but this hypothe- 

 sis would not bear a moment's examination. Others wished to 

 discover in them certain effects of diffraction, or of refraction. — 

 But the touch-stone of all theories is calculation ; and uncertainty 

 the most indefinite must follow, in reference to their application 

 to the remarkable phenomena specified, those, namely, of which 

 we have just been speaking. Explanations, giving neither an 

 exact account of the height,' the form, the color, nor the fixity of 

 a phenomenon, ought to have no place in science. Let us come 

 to the idea, much extolled for a short time, that the protuberances 

 were solar mountains, whose summits extend beyond the photo- 

 sphere covered by the moon at the moment of observation. Fol- 

 lowing the most moderate computations, the elevation above the 

 solar disc of one of these summits, would have been 19,000 

 leagues. I am well aware that no argument because based on 

 the vastness of this height, should lead to the rejection of the 

 hj-pothesis, but it may be much shaken by remarking that these 

 pretended mountains exhibit considerable portions beyond the 

 perpendicular, which consequently in virtue of the solar attraction 

 must have fallen down. 



Let us now take a rapid glance of the hypothesis, according 

 to which the protuberances would be assimilated to solar clouds 

 floating in a gaseous atmosphere. Here we find no principle of 

 natural philosophy to prevent our admitting the existence of 

 cloudy masses from 70,000 to 90,000 miles in length, with their 

 outlines serrated, and assuming the most distorted forms, only in 

 further pursuing this hypothesis, one could not fail to be aston- 

 ished that no solar cloud had ever been seen entirely separate 

 from the circumference of the moon. It is towards this deter- 

 mination, the subject otherwise eluding us, that researches of 

 astronomers should be directed. A mountain being incapable 

 of sustaining itself without a base, the fortuitous observation of 

 a prominence, separated in appearance from the margin of the 

 moon, and consequently, from the real margin of the solar pho- 

 tosphere, should be sufficient utterly to overthrow the hypothesis 

 of solar mountains. Such an observation has really been made. 

 M. Kutochi who observed the eclipse of July Sth, 1850, writes: 

 " the slender and redish stiiated appearance which was found 

 near the northern prominence seemed to be completely detached 

 from the margin of the moon." In the eclipse of the 28th of 

 Jul)', 1851, Messrs. Mauvais and Soujon, of Dantzic, and the 

 celebrated foreign astronomers who had repaired to the different 

 parts of Norway and the north of Germany, saw in all the se- 

 lected stations without exception, a spot uniformly red, and 

 separated from the limb of the moon. These observations put 

 a definite termination to the explanations of the protuberances, 

 founded on the supposition that there existed in the sun, moun- 

 tains whose summits would reach considerably above the photos- 

 phere. When it shall bo clearly demonstrated that these luminous 

 phenomena cannot be the effect of the inflexions which the solar 

 rays might experience in passing near the rough parts which 

 fringe the circumference of the moon ; when it shall be demon- 

 strated that these rosy tints cannot be assimulated to simple 

 optical appearances, and have, in truth, a real existence, that 

 they are not real solar clouds, it will then be necessary to add a 

 new atmosphere to the two of which we have spoken ; for these 

 clouds cannot be sustained in vaccuo. The existence of a third 

 atmosphere is moreover established by phenomena of quite 

 another nature, namely, by the comparative intensity of the 



