398 SCIENTIFIC RECORD FOR 1885. 



" There can be no doubt that the corona shows us matter existing 

 about the sun in the form of a fog, of which we may form some idea by 

 imagining the air we breathe very much rarefied but still full of par- 

 ticles rendered visible by a sun's ray. The matter of the corona sends 

 us three kinds of light : Solar light dispersed by particles of matter, 

 either solid or liquid ; light giving a continuous spectrum, showing that 

 the solid or liquid particles are incandescent, and light giving spectra 

 of brilliant lines, fainter and varying greatly at diiferent parts of the 

 corona and at different eclipses, which must be due to the presence of a 

 luminous gas. This gas existing between the particles does not form a 

 solar atmosphere in the true sense of the word (such an atmosphere has 

 already been shown to be impossible), but this gas may be regarded as 

 carried along by the particles ; it is due perhaps to the heat of the suu. 



" Comets show characteristics which are not without analogy to those 

 of the corona ; in the case of comets we see reproduced on a small scale 

 the luminous streams, the rifts and curved rays.* We do not know 

 the conditions under which these cometary appearances occur, but the 

 generally accepted hypothesis attributes them to electrical action, and 

 especially to a repulsive force acting from the sun, and doubtless an 

 electrical force, which varies with the surface, and not, like gravity, 

 with the mass. A force of this nature could easily overcome the force 

 of gravity, and, as we see in the tails of comets, drive very much rare- 

 fied matter to immense distances. Such a repulsive force, if electrical in 

 its origin, must act between bodies charged with the same kind of elec- 

 tricity, and according to this theory the material of which the corona is 

 composed and the surface of the sun must be in the same electrical 

 state ; a certain permanence of the same electrical state would seem to 

 be required by the phenomena of the tails of comets ; but we are quite 

 in ignorance on this subject. 



" However this may be, it is quite in conformity with the ideas ex- 

 pressed above, that the positions of greatest coronal extension should 

 usually correspond with the spot zones where the solar activity is great- 

 est. A careful investigation of the structure of the corona leads us to 

 think also that the forces to which this complicated and variable struct- 

 ure is due have their seat in the sun. Matter repelled by the sun 

 would participate in the rotary velocity of the photosphere, and lagging 

 behind give rise to curved forms. Moreover, the force of the projection 

 and the subsequent electrical repulsion might very well vary in direc- 

 tion and not be always strictly radial, and this would help to exi)lain 

 the character of the corona. The relative permanency of some of the 

 coronal forms during several weeks does not imply that the matter is 

 immovable ; flames over the mouths of volcanoes often offer a similar 

 appearance. If the forces to which the corona is due reside in the 

 sun, the corona ought, of course, to revolve with it 5 but if the corona is 

 produced by causes extraneous to the sun, it may be otherwise. 



*See "Comets," Boyal Institution Proceedings, Vol. x, p, 1, 



