ECLIPSES. 



not exceed the sum of their apparent semi-diameters, which 

 never much exceeds half a degree, it is clear that an eclipse can 

 never happen except when, at the time of conjunction, the appa- 

 rent distance of the moon's centre from the ecliptic is within 

 that limit, a condition which can only be fulfilled within certain 

 small distances of the moon's nodes. 



There is a certain distance from the moon's node, beyond which 

 a solar eclipse is impossible, and a certain lesser distance, within 

 which that phenomenon is inevitable. These distances are called 

 the solar ecliptic limits. 



24. Columbus is said to have availed himself of his acquaint- 

 ance with practical astronomy to predict a solar eclipse, and used 

 the prediction as a means of establishing his authority over the 

 crews of his vessels, who showed indications of mutinous dis- 

 obedience. 



The spectacle presented during a total eclipse is always most 

 imposing. The darkness is sometimes so intense as to render the 

 brighter stars and planets visible. A sudden fall of temperature 

 is sensible in the air. Vegetables and animals comport them- 

 selves as they are wont to do after sunset. Flowers close, and 

 birds go to roost. Nevertheless, the darkness is different from 

 the natural nocturnal darkness, and is attended with a certain 

 indescribable unearthly light, which throws upon surrounding 

 objects a faint hue, sometimes reddish, and sometimes cada- 

 verously green. 



Many interesting narratives have been published by scientific 

 observers who have been so fortunate as to witness these 

 phenomena. 



25. When the disc of the moon, advancing over that of the 

 sun, has reduced the latter to a thin crescent, it was observed by 

 Mr. Francis Baily, that immediately before the beginning, or after 

 the end of complete obscuration, the crescent appeared as a band 

 of brilliant points separated by dark spaces, so as to give to it the 

 appearance of a string of brilliant " beads." The phenomenon, 

 which has since been frequently re-observed, thence acquired the 

 name of " Baily' s beads." 



Further observation showed, that, before the formation of the 

 "beads, "the horns'of the crescent were sometimes interrupted 

 and broken by black streaks thrown across them. 



These phenomena are roughly sketched in figs. 7, 8. 



Figs. 9, 10, 11, 12, are taken from the original sketches of Mr. 

 Baily, representing the progressive disappearance of the beads 

 after the termination of the complete obscuration. 



26. These phenomena arise from the projections of the edge of 

 the moon's disc, serrated by numerous inequalities of the surface, 



168 



