58 



an hour for the moon to advance over the sun till it com- 

 pletely conceals it, — time which is of little use for other 

 purposes, — there is an excellent opportunity for such 

 observations. This is one use of eclipses. Formerly it 

 was considered the only scientific way to observe the 

 phenomenon. Dr. Bowditch, who observed the eclipse 

 of 1806 in Salem, devotes his report entirely to the cor- 

 rections to the moon's place determined by his own and 

 others' observations. He simply mentions the fact that 

 a luminous appearance surrounded the moon, as had 

 been noted in previous eclipses. 



But this "luminous appearance" is now the most inter- 

 esting object of an eclipse, and the invention of new in- 

 struments unknown to the great mathematician makes it 

 possible to study it with success. The special features 

 of the total phase of an eclipse, I need not remind you, 

 are the corona or halo of light surrounding the eclipsed 

 sun and the solar prominences which seem to be clinging 

 to the limb of the moon. Upon the blackboard is a rep- 

 resentation of the corona as it appeared in a telescope of 

 5 J inches aperture. The northern and southern portions 

 were separated into distinct beams of light, curving on 

 each side from the north and south line ; the eastern and 

 western portions were radiated in structure, but not 

 divided into distinct beams. There was one beam on the 

 western portion which seemed to cross the radiated struc- 

 ture curving towards the south. The star d Coronas 

 shone brightly through the corona. 



The solar prominences were not conspicuous in this 

 eclipse. In the eclipses of 1860 and 1870 they were 

 very abundant. In 1860 the largest one was found to be 

 nearly 100,000 miles high or one-ninth of the sun's diam- 

 eter. In that eclipse, it was proved that they belonged 

 to the sun and not to the moon, as the latter passed over 



