ON THE SOLAR CORONA. 767 



descent fog, which at the same time scatters to us the photospheric 

 light. Now, we must bear in mind the very different behavior of a 

 gas, and of liquid or solid particles in the near neighborhood of the 

 sun. A gas need not be greatly heated, even when near the sun, by 

 the radiated energy. Heated gas from the photosphere would rapidly 

 lose heat ; but, on the other hand, liquid or solid particles, whether 

 originally carried up as such or subsequently formed by condensation, 

 would absorb the sun's heat, and at coronal distances would soon rise 

 to a temperature not very greatly inferior to that of the photosphere. 

 The gas which the spectroscope shows to exist along with the incan- 

 descent particles of the coronal stuff may therefore have been carried 

 up as gas or have been in part distilled from the coronal particles 

 under the enormous radiation to which they are exposed. Such a view 

 would not be out of harmony with the very different heights to which 

 different bright lines may be traced at different parts of the corona 

 and at different eclipses. For obvious reasons, gases of different 

 vapor density would be differently acted upon by a repulsive force 

 Avhich varies as the surface, and would to some extent be winnowed 

 from each other ; the lighter the gas the more completely would it 

 come under the sway of repulsion, and so would be carried to a greater 

 height than the gas more strongly held down by gravity. The rela- 

 tive proportions, at different heights of the corona, of the gases which 

 the spectroscope shows to exist there (and recently Captain Abney and 

 Professor Schuster have shown that in addition to the bright lines al- 

 ready known the spectrum of the corona of 1882 gave the rhythmical 

 group of the ultra-violet lines of hydrogen which are characteristic of 

 the photographic spectra of the white stars, and some other lines also) 

 would vary from time to time, and depend in part upon the varying 

 state of activity of the photosphere, and so probably establish a con- 

 nection with the spectra of the prominences. This view of the corona 

 would bring it within the charmed circle of interaction which seems 

 to obtain among the phenomena of sun-spots and terrestrial magnetic 

 disturbances and aurora?. 



Many questions remain unconsidered ; among others, whether the 

 light emitted by the gaseous part of the corona is due directly to the 

 sun's heat, or to electrical discbarges taking place in it of the nature 

 of the aurora. Further, what becomes of the coronal matter on the 

 theory which has been suggested ? Is it permanently carried away 

 from the sun, as the matter of the tails of comets is lost to them ? 

 Among other considerations it may be mentioned that electric repul- 

 sion can maintain its sway only so long as the repelled particle remains 

 in the same electrical state : if through electric discharges it ceases to 

 maintain the electrical potential it possessed, the repulsion has no more 

 power over it, and gravity will be no longer mastered. If, when this 

 takes place, the particle is not moving away with a velocity sufficient- 

 ly great to carry it from the sun, the particle will return to the sun. 



