452 Mu. G. J. Stoncy on the Bearing of 



and the photosphere. There can be little doubt now that this 

 shell of clouds, which I erroneously supposed lay almost in con- 

 tact with the hot stratum over the photosphere, is in reality no 

 other than the long-sought boundary of the atmospheres of iron 

 and of the other gases near it in vapour-density, and that the 

 spectrum seen by Captain Haig will, when examined through a 

 sufficiently fine slit, prove to be that spectrum of bright lines 

 coincident with the fainter of the dark lines of ordinary sunlight, 

 to which I last year took the liberty of asking the attention of 

 the observers*. It is a matter equally of interest and import- 

 ance to ascertain whether this bright spectrum may not be ob- 

 served in the absence of an eclipse, in the way in which the 

 spectra of protuberances have been made out by Messrs. Lockyer 

 and Janssenf. 



105. The whole of the light, however, which is seen with the 

 telescope in this bright region cannot emanate from these spec- 

 tral lines, although most of what is seen with the spectroscope 

 probably does. For light from this class of spectral lines would 

 maintain its brightness up to the edge of the solar disk, whereas 

 the observations of 1860 point to the existence also of a shell of 

 luminous matter (see latter part of § 66). Now, when we bear 

 in mind what is said in § 64, I think we may presume that 

 iron and several of the metals grouped about it in vapour-density 

 (viz. the least volatile in an atmosphere of hydrogen of the metals 

 calcium, chromium, manganese, nickel, cobalt, copper, zinc, and 

 no doubt also barium, §§ 49 & 82) behave in the way indicated 

 in that paragraph : — that their natural level in the sun's atmo- 

 sphere is higher than the level they actually attain ; that they 

 are constantly making their way upwards, and as constantly pre- 

 cipitated by the increasing cold in a mist of liquid or solid par- 

 ticles which constitutes a shell of cloud conspicuous through the 

 telescope and in photographs, but which will present with the 

 spectroscope the appearance of a faint groundwork upon which 

 bright lines from the subjacent gases will be seen] projected. 

 The hot space within is filled with a mixture of all the consti- 

 tuents J of the sun's atmosphere; but throughout the enormous 



* See a note published in the Monthly Notices of the Astronomical 

 Society for December 13, 1867, and in Phil. Mag. S. 4. vol. xxxiv. p. 502. 



t Proceedings of the Roval Society, vol. xvii. p. 91; and Comptes 

 Rendus of October 26, 1868," pp. 836 & 838. 



X The narrowness of the sodium and hydrogen lines in the solar spectrum 

 (see footnote to § 39) would almost tempt one to conjecture that the stra- 

 tum of cloud is the lower limit of the free hydrogen and sodium, if such a 

 thing be possible, as well as the upper limit of the iron group of metals, 

 and that the hydrogen and sodium, according as they diffuse downwards, 

 either enter into some kind of union with metals or in some other way 

 become so modified that they do not emit their usual spectra. Silver at a 



