3fS8 



THE ILIAIMINATION OF THE ECLIPSED MOON. 



nearer the moon is to the earth, in a lunar eclipse, the greater 

 will bo the obstruction in the way of the sun's rays reaching 

 it; the farther the moon is from the earth, tlio purer and 

 brighter will be the light which it receives. 



In testing this view by a reference to actual instances, I 

 would use the same caution that I used with regard to the 

 corona. Yet I am tempted to mention that out of four 

 eclipses, the particulars of which I find available, three lend 

 a fair support to my theory. In the bright eclipse of March, 

 1848 (already referred to), the moon was within, three days 

 of apogee, and in the dark eclipse of October, 1884, the 

 moon was within three days of perigee. The eclipse of 

 January last, which was probably of about average bright- 

 ness, occurred nearly midway between apogee and perigee. 

 Where two or more causes combine to produce an effect, 

 complete accordance with either one of them is not to be 

 expected. 



In all that has preceded, my remarks and calculations 

 have had special reference to the central axis of the earth's 

 shadow, or to the moon when centrally eclipsed. The 

 problem of the moon's illumination, even when thus 

 narrowed, is not free from difficulty ; it acqiiires additional 

 complexity when, we include in our consideration the vary- 

 ing amount of illumination in different parts of the moon's 

 disc, or of the whole disc in diiforent stages of the eclipse 

 — in other words, the varying amount of light in diflFerent 

 parts of a transverse section of the earth's shadow. 



Some of the differences observable in the brightness of 

 different parts of the eclipsed moon — and possibly all the 

 irregular or patchy differences observable — may be ascribed 

 to differences in the light-reflecting quality of different 

 parts of the lunar surface, these differences being revealed 



