THE SOLAR ECLIPSE OF 1871. 99 



such observations have been made independently ; the 

 phenomenon is but instantaneous, a mere flash of bright 

 stripes in place of dark lines across the colored riband of 

 the spectroscope, which happens just at the moment be- 

 fore and after totality, and is presented only when the 

 instrument is accurately directed to the delicate curved 

 vanishing thread of light which is the last visible frag- 

 ment of the solar outline, and that which makes the first 

 flash of his re-appearance. 



A little explanation is necessary to render the signifi- 

 cance of this "reversal" intelligible to those who have 

 not specially studied the subject. 



1st. When the spectroscope is directed to a luminous 

 solid a simple rainbow-band or " continpus spectrum" is 

 seen. When, on the other hand, the object is a luminous 

 gas or vapor of moderate density, the spectrum is not a 

 continuous band with its colors actually blending ; it con- 

 sists only of certain luminous stripes with blank spaces 

 between them, each particular gas or vapor showing its own 

 particular set of stripes of certain colors, and always ap- 

 pearing at exactly the same place, so invariably and cer- 

 tainly, that, by means of such luminous stripes, the compo- 

 sition of the gas or vapor may be determined. If, however, 

 the gas be much compressed, the stripes widen as the con- 

 densation proceeds ; they may even spread out sufficiently 

 to meet and form a continuous spectrum like that from a 

 solid. Liquids also produce continuous spectra. 



3d. When a luminous solid or liquid, or very dense gas, 

 capable of producing a continuous spectrum, is viewed 

 through an intervening body of other gas or vapor of 

 moderate or small density, fine dark lines cross the spec- 

 trum in precisely the same places as the bright stripes 

 would appear if this intervening gas or vapor were lumi- 

 nous and seen by itself. 



When the spectroscope is directed to the face of the sun 

 under ordinary circumstances, it presents a brilliant con- 

 tinuous spectrum, striped with a multitude of the dark 

 lines. From this it has been inferred that the luminous 

 face of the sun is that of an incandescent solid or liquid, 

 and that it is surrounded by the gases and vapors whose 



