82 LIGHT SCIENCE FOR LEISURE HOURS. 



more important than that of last year, and the length 

 of the actual track of the moon's shadow considerably 

 greater. The third eclipse of the series will occur on 

 November 30, 1872. In one respect it will be one of 

 the most remarkable ever recorded ; for it must be 

 described as at once an annular and a total eclipse of 

 the sun. This is readily explained, though the occur- 

 rence is altogether exceptional. The reader is aware 

 that the point of the moon's conical shadow sometimes 

 extends beyond and sometimes falls short of the earth. 

 In the former case an eclipse is total, in the latter it is 

 annular. But in the eclipse of November 30, 1872, 

 the apex of the shadow falls short of the earth's surface 

 at the beginning of the eclipse ; it encounters the 

 earth as the shadow-track passed onwards towards the 

 bulging central part of the earth's illuminated hemi- 

 sphere ; and presently, towards the close of the eclipse, 

 falls again short of the earth's surface. So that there 

 are two points on the earth's surface where, on 

 November 30, 1872, the eclipse will be exactly total, 

 the moon just hiding the sun and no more, and only 

 for a single instant. The totality will nowhere last 

 more than about three-quarters of a minute ; and as 



on the 1 2th inst., as at the middle of the transit of Venus, on De- 

 cember 8, 1874. The fifteen pictures of the rotating earth, in Plate 

 VIII. of my treatise on the sun, illustrate the approaching eclipse as 

 exactly as though drawn for the purpose. The first shows the earth's 

 face as seen from the sun just before the moon's passage begins ; the 

 next thirteen show the earth's face at successive intervals of a quarter 

 of an hour during the progress of the eclipse ; and the last shows the 

 earth's face as seen from the sun just after the moon has passed off 

 that face. 



