134 



On the Corona of the Sun. 



in an increasing faintness and diffusion. The absence of a limit is 

 probably true only of the faint outer parts of the corona. Within, 

 and especially about the distance from the sun's, limb to which the 

 so-called " inner corona " usually extends, there is evidence of an 

 apparent arrest of coronal matter, due in part probably to the effects 

 of perspective, and within this distance are seen numerous rays which 

 turn round and descend towards the sun. These returning curved 

 forms are well shown in Mr. Wesley's drawings of the eclipse of 1871.* 



We are led to the conclusion that many of the coronal particles 

 return to the sun, but that in the case of other particles which form 

 the stronger coronal rays and streamers, there is no return, but that 

 they leave the sun, and, at the same time, separate more widely from 

 each other by their mutual repulsion, and become too diffused to be 

 visible. The state of extreme attenuation of this diffused coronal 

 matter — such that the nuclei of comets pass through it without 

 sensible retardation, enables us to see that the corona may be main- 

 tained at an extremely small expenditure of solar material. Among 

 other considerations it may be mentioned that an electric repulsion 

 can maintain its sway only so long as the repelled particles remain 

 in the same electrical state ; if through electric discharges the parti- 

 cles cease to maintain the electric potential they possess, there will 

 be no longer any force of repulsion acting upon them, and gravity 

 will be no longer mastered. If when this takes place, the particle 

 is not moving away with a velocity sufficiently great to carry it 

 from the sun, the particle will return to the sun. Of course, if the 

 effect of any electric discharges or other local conditions has been 

 to change the potential of the particle from positive to negative, 

 or the reverse, as the case may be, then the repulsion would be 

 changed into an attraction acting in the same direction as gravity. 



This ceaseless outflow of extremely minute particles, very widely 

 separated from each other, may possibly throw some light on another 

 phenomenon which has not yet been satisfactorily explained, namely, 

 the zodiacal light. 



The views which I have ventured to put forward in this lecture 

 would lead us to expect that a more extended and more brilliant 

 corona surrounded the sun in early geological time, and that if the 

 skies were then of their present degree of clearness, the corona would 

 probably have been visible about the sun. 



May the corona have been still faintly visible in the earliest ages of 

 the human race ? Are there any philological traces of it in the 

 earliest words and ideas connected with the sun ? 



On those eastern plains, where the air is of so great purity, did 

 early men still see faintly a true 7ra/)jj\<o«? ? 



Similar considerations point to a slow secular diminution in extension 

 # " Mem. Roy. Astron. Soc," vol. xli, Plates 6, 7, 8, and 10. 



