ASTRONOMY. 399 



"We have seen that the coroua probably cousists of an incandescent 

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

 ])hotosi)here. 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 lieated even when 

 near the sun by the radiated energy ', when onc<', 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 at the distance of the corona 

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

 The gas shown by the wspectroscope to exist among the incandescent 

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

 may have been in part distilled from the coronal i^articles under the 

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

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

 at which the brilliant lines in the corona, have been observed, (xases 

 of unequal densities, unequally repelled by a repulsive for(;e 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 proi)ortions at different heights of 

 the corona of the gases, whose i)resence is shown by the spectroscope, 

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

 the photosi)here in such a way as to establish a probable connection with 

 the spectrum of the protuberances. (Captain Abney 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 Hues 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- 

 rora}, 



" 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 repulsion must cease, and, gravity no 

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

 AVesley's drawings of the corona, especially in those of t,he 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.* 



* Conceraing the naturo of the corona cousTilt the papers of Nortitii, Yonu<,^, and 

 Langley in the American Journal of Science, The Snn, hy Professor Young, and various 

 essays by Mr. 11. A. Proctor. 



