170 NOTE ON THE TOTAL ECLIPSE OF THE MOON. 
real nature of the corona may be, no doubt remains of its 
existence as an actual luminous body surrounding the sun. 
From the degree to which its light mitigates the darkness on 
the earth in a total eclipse of the sun, we may form an estimate 
ef the degree to which it will illuminate the moon in that which 
is to the moon a total eclipse of the sun. It is true the illumina- 
tion will not he equal in the two cases, because the earth, being 
very much larger than the moon, will intercept to the moon a 
very much larger portion of the corona than the moon can 
intercept to us, and the portion so intercepted will include all 
the more central and brighter parts ; still, even so, enough may 
remain, and it must be remembered that the ‘fainter parts of 
the corona probably extend very far beyond what has been 
actually seen. Whether the amount of light given out by the 
corona varies greatly at different times, may not be easy to 
prove, but at least it may be said that the inconstancy of form 
and general appearance which the corona has exhibited in 
different eclipses, renders such variation probable. This being 
admitted, we have only further to assume that in the rare 
instances in whiclr the eclipsed moon becomes invisible, the 
light of the solar corona is at its minimum, and the explanation 
is complete. Possibly, in course of time, with improved methods 
of investigation, this coincidence of the two phenomena, at 
present a speculation, may become an observed fact. 
