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THE ILLUMINATION OP THE ECLIPSED MOON. 



I hope I may now claim to liave shown that the problem 

 under discussion has not, up to the present time, been 

 satisfactorily solved, and that an effort to elucidate it 

 further is not at all events superfluous. 



In some remarks on the eclipse of October, 1884, which I 

 made at one of our meetings, I throw out the suggestion 

 that the eclipsed moon might possibly be in some slight 

 degree self-luminous. Since the recent eclipse, I observe 

 that the same idea has been put forward by an Italian 

 astronomer. I think it is not altogether unworthy of con- 

 sideration, for we know that tliere are substances in nature 

 which even at ordinary temperatures are phosphorescent, 

 and there are other substances which become phosphor- 

 escent when heated. The moon, having no atmosphere to 

 shelter it from the fierce rays of the sun, must be exposed 

 to intense heat, and might possibly continue to shine feebly 

 after the solar rays had been withdrawn. Still, this ex- 

 planation at the best is very incomplete, for it gives lis no 

 account of that which is the only real puzzle in the case, 

 namely, the varying luminosity at different times. 



The idea which I broached in my published account of 

 the eclipse of October, 1884, deserves, I think, a little more 

 attention. I suggested that the solar corona might be an 

 important source of light to the moon during total eclipse, 

 and that the varying amount of light might bo connected 

 with the known variations in the brightness of the corona 

 at different times. The corona, as seen from the earth in a 

 total eclipse of the sun, is a very bright object. It has boon 

 described as dazzling in its brightest part, and the total 

 amount of light emitted by it has been estimated as equal 

 to that of the full moon. The moon in eclipse will not 

 receive nearly that amount of light, because the earth will 

 intercept all the more coutral and brighter parts of the 



