XXIV 

 COMETS 



A COMET is so called from the hair-like stream of 

 light or " tail," which stretches to a greater or less 

 length from its bright head or " nucleus." A large comet, 

 when seen to greatest advantage, may have a tail which 

 stretches across one-third of the "vault of heaven," and 

 may be reckoned by astronomers at as much as one 

 hundred and twenty million miles long. Donati's comet 

 which some of my readers will remember, as I do, when 

 it visited us in 1858 was of this imposing size. Halley's 

 comet, on the other hand, when it was last " here," namely, 

 in 1835, showed a tail estimated by astronomers to be fifty 

 million miles long. The tail was more than twice as long 

 when Halley's comet appeared in 1456. There was a big 

 comet " on view "in 181 1 the year celebrated for its wine 

 and in recent times a fine comet appeared in 1861, and 

 another (Coggia's comet) in 1874. 



The ancient records of comets are naturally full of 

 exaggeration. Up to Milton's time two hundred and 

 fifty years ago they caused the greatest terror and excite- 

 ment by their sudden appearance in the sky. This is due 

 to the fact that mankind from the very earliest periods of 

 which we have record has not merely gazed at the " starry 

 host" by night in solemn wonder, but even in early 

 prehistoric times studied and watched the stars so as to 



