nf iron, which, by the way, Justifies us in 

 concluding what nn enormously high temper- 

 ature must prevail there. It shows, more- 

 .<\ or, how our Figs. 5, C, and 7 indicate 

 iron, calcium, and sodium, and also the pres- 

 ence of hydrogen, of zinc, of copper, and of 

 the metals of magnesia, alumina, baryta, and 

 >th-r terrestrial elements. Lead, on the 

 btLer hand, is wanting, as well as gold, silver, 

 mercury, antimony, arsenic, and some others. 

 The spectra of several fixed stars are simi- 

 larly constituted ; they show systems of fine 

 lines which can be identified with those of 

 terrestrial elements. In the atmosphere of 

 Aldebaran in Taurus there is, again, hydro' 

 gen, iron, magnesium, calcium, sodium, and 

 also mercury, antimony, and bismuth ; and, 

 according to H. C. Vogel, there is in a Orionis 

 the rare metal thallixim ; and so on. 



We cannot, indeed, say that we have ex- 

 plained all spectra ; many fixed stars exhibit 

 peculiarly banded spectra, probably belong- 

 ing to gases whose molecules have not been 

 completely resolved into their atoms by the 

 high temperature. In the spectrum of the 

 sun, also, are many lines which we cannot 

 identify with those of terrestrial elements. 

 It is possible that they may be due to sub 

 stances unknown to us, it is also possible 

 that they are produced by the excessively 

 high temperature of the sun, ff.r transcend- 

 ing anything we can produce. But this is 

 certain, that the known terrestrial substances 

 are widely diffused in space, and especially 

 nitrogen, which constitutes the greater part 

 nf onr atmosphere, and hydrogen, an element 

 in water, which indeed is formed by its com- 

 bustion. Both have been found in the irre 

 solvable nebula?, and, from the inalterability 

 of their shape, these must be musses of 

 enormous dimensions and at an n<>rimms 

 distance. For this reason Hir W. jit>j-scuu 



POPULAII SC::::TTIFIC ^^^IOJL.^O. 625 



considered that they did not belong to the 

 system of our fixed stars, but were represent- 

 atives of the manner in which other systems 

 manifested themselves. 



Spectrum analj-sis has further taught us 

 more about the sun, by which he is brought 

 nearer to us, as it were, than could formerly 

 have seemed possible. You know that the 

 sun is an enormous sphere, whoso diameter 

 is 112 times an great as that of the earth. 

 We may consider what we see on its surface 

 as a layer of incandescent vapor, which, to 

 judge from the appearances of the sun-spots, 

 has a depth of about 500 miles. This layer 

 of vapor, which is continually radiating heat 

 on the outside, and is certainly cooler than 

 the inner masses of the sun, is, however, 

 hotter than all our terrestrial flames hotter 

 even than the incandescent carbon points of 

 the electrical arc, which represent the highest 

 temperature attainable by terrestrial means. 

 This can be deduced with certainty from 

 Kirchhoffs law of the radiation of opaque 

 bodies, from the greater luminous intensity 

 of the sun. The older assumption, that the 

 sun is a dark cool body, surrounded by u 

 photosphere which only radiates heat anil 

 light externally, contains a physical impossi- 

 bility. 



Outside the opaque photosphere, the sun 

 appears surrounded by a layer of transparent 

 gases, which are hot enough to show in the 

 spectrum bright colored lines, and are hence 

 called the Chromosphere. They show tho 

 bright lines of hydrogen, of sodium, of mag- 

 nesium, and iron. In these layers of gas and 

 of vapor about the sun enormous stormw 

 occur, which are as much greater than those 

 of our earth in extent and in velocity as the 

 sun is greater than the earth. Currents of 

 ignited hydrogen burst out several thousands 

 of miles high, like gigantic jets or tongues of 

 flame, with clouds of smoke above them.* 

 These structures could formerly only be 

 viewed at the time of a total eclipse of the 

 sun, forming what were called the rose-red 

 protuberances. We now possess a method, 

 devised by MM. Jansen and Lockyer, by 

 which they may at any time be seen by the 

 aid of the spectroscope. 9 



On the other hand, there vre individual 

 darker parts on the sun's surface, what are 

 called sun-spots, which were seen as long ago 

 as by Galileo. They are funnel-shaped, the 

 sides of the funnel are not so dark as the 

 deepest part, the core. Fig. 8 represents 

 such a spot according to Padre Secchi, as 

 seen under powerful magnification. Theii 

 diameter is often more than many tens oJ 

 thousands of miles, so that two or three 

 earths could lie in one of them. These spots 

 may stand for woeks or months, slowly chang 

 ing, before they are again resolved, and mean' 

 while several rotations of the sun may takv 

 place. Sometimes, however, there are very 

 rapid changes in them. That the core if 

 il.'cpor than the edge of the surrounding 

 penumbr.i follows from their respective di 

 placements as they come near the edge, arid 

 uro therefore seen in a very oblique direction. 



