I 



ASTRONOMY. 399 



" We have seen that the corona inobably consists of an incandescent 

 fog, which, at the same time, sends us by reflection the light of the 

 photosphere. Now we must remember that there is a great difference 

 in the behavior of a gas and of liquid and solid particles in the imme- 

 diate vicinity of the sun. A gas need not be greatly heated even when 

 near the sun by the radiated energy ; when once heated it would rap- 

 idly lose its heat when above the photosphere; but solid and liquid 

 particles, whether carried up as such or having become such by con- 

 densation, would absorb the sun's heat and ac the distance of the corona 

 would reach a temperature but little inferior to that of the photosphere. 

 The gas shown by the spectroscope to exist among the incandescent 

 matter of the corona may therefore have been carried there as gas or 

 may hav^e been in part distilled from the coronal particles under the 

 influence of the enormous solar radiations. There would be no discord- 

 ance between this theory and the fact of the very different heights 

 at which the brilliant lines in the corona have been observed. Gases 

 of unequal densities, unequally repelled by a repulsive force varying as 

 the surface, would be to a certain degree separated, the highest gas 

 being most influenced by the repulsive force, the heaviest being most 

 influenced by gravity. The relative proportions at different heights of 

 the corona of the gases, whose presence is shown by the spectroscope, 

 vary from time to time and depend in part upon the state of activity of 

 the photosphere in such a way as to establish a probable <onnection with 

 the spectrum of the protuberances. (Captain Abuey and Professor 

 Schuster have recently shown that beside the bright lines already 

 known, the spectrum of the corona of 1882 gave the group of the ultra- 

 violet lines of hydrogen, which are characteristic of the photographic 

 spectra of white stars, and other liaes also.) In this view of the corona, 

 therefore, we find a new example of such relations as those existing be- 

 tween the phenomena of sun spots and magnetic perturbations or au- 

 rorae. 



" Many questions are left unconsidered, this among others, whether the 

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

 sun's heat or to electrical discharges of the nature of the aurora. Fur- 

 ther, 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 ? Electric repulsion can continue 

 only so long as the repelled particles remain in the same electrical state. 

 If the electrical state changes, the rejiulsion must cease, and, gravity no 

 longer counteracted, the particle must fall back to the sun. In Mr. 

 Wesley's drawings of the corona, especially in those of the eclipse of 

 1871, the longer rays or streamers seem not to end but to be lost in the 

 fainter parts of the drawing ; but some of the shorter ones seem to turn 

 and descend to the sun.* 



* Concerning the nature of the corona consult the papers of Norton, Young, and 

 Langley in the American Journal of Science, llie Sun, by Professor Young, andvurioufl 

 essays by Mr. R. A. Proctor. 



