THE STORY OF NINETEENTH-CENTURY SCIENCE 



ominous clan in the minds of all snperstitious genera- 

 tions. 



It is true a hard blow was struck at the prestige of 

 these alleged supernatural agents when Newton proved 

 that the great comet of 1680 obeyed Kepler's laws in its 

 flight about the sun ; and an even harder one when the 

 same visitant came back in 1758, obedient to Halley's 

 prediction, after its three-quarters of a century of voy- 

 aging out in the abyss of space. Proved thus to bow to 

 natural law, the celestial messenger could no longer 

 fully sustain its role. But long-standing notoriety can- 

 not be lived down in a day, and the comet, though 

 proved a " natural " object, was still regarded as a very 

 menacing one for another hundred years or so. It re- 

 mained for our own century to completely unmask the 

 pretender, and show how egregiously our forebears had 

 been deceived. 



The unmasking began early in the century, when Dr. 

 Olbers, then the highest authority on the subject, ex- 

 pressed the opinion that the spectacular tail, which had 

 all along been the comet's chief stock in trade as an 

 earth - threatener, is in reality composed of the most 

 filmy of vapors, repelled from the cometary body by the 

 sun, presumably through electrical action, with a veloc- 

 ity comparable to that of light. This luminous sug- 

 gestion was held more or less in abeyance for half a cen- 

 tury. Then it was elaborated by Zollner, and particu- 

 larly by Bredichin, of the Moscow observatory, into 

 what has since been regarded as the most plausible of 

 cometary theories. It is held that comets and the sun 

 are similarly electrified, and hence mutually repulsive. 

 Gravitation vastly outmatches this repulsion in the 

 body of the comet, but yields to it in the case of gases, 



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