MOON-, EECENT OBSERVATIONS AND STUDY OF THE. 



581 



reassemble at the center of the mass. In the 

 early stages of this reassembling the solid globe 

 becomes distinctly visible, but is soon obscured 

 in the condensing vapors, and the same body, 

 if caught sight of, on its next return to perihe- 

 lion, before the solar heat has progressed far 

 in evolving vapors from its surface, will be seen 

 as a well-defined globe surrounded by a thin 

 mantle of vapor. That comets are " visible 

 nothingness," "negative shadows," etc., are 

 merely expressions constructed in response to 

 a theory that strangled the science of astrono- 

 my in its cradle two centuries ago, and its as- 

 sumption of authoritative dictation has made 

 men afraid to verify the controverting facts 

 that present themselves in overwhelming 



matic telescope, it presented a planetary disk." 

 The planet Venus, when nearest to the earth, 

 does not measure 2' of are, and when Herschel 

 measured the disk of Halley ? s comet it was 

 much farther from the earth than Venus, hence 

 its globe must have been considerably larger 

 than either Venus or the earth. 



To furnish the illustration we require, we 

 have only to imagine the eccentricity of the 

 earth's orbit to be what it was in a period of 

 the past, net even as far back as its beginning; 

 and through the vicissitudes in which such an 

 orbit would involve it, let us follow its fortunes 

 for a while. When, in its advance from space, 

 it was half-way toward this new perihelion, 

 four times as many sun-rays would f:ill upon 



THE CLEFT OP THE LUNAR ALPS. 



abundance. Even Sir John Herschel, while 

 giving expression to views that plainly indi- 

 cate his suspicions that comets are but younger 

 members of the family of worlds, takes the 

 precaution to hedge, lest he might be looked 

 upon as recreant to the theory. In his " Out- 

 lines of Astronomy," writing of Halley's comet 

 at the time of the reassembling of its globe, 

 after perihelion, he says, "It no longer pre- 

 sented any vestige of tail, but appeared to the 

 naked eye as a hazy star of about the fourth or 

 fifth, magnitude, and in powerful telescopes as 

 a small, round, well-defined disk, rather more 

 than 2' in diameter." He also says, " When- 

 ever powerful telescopes have been turned on 

 these bodies, they have not failed to dispel the 

 illusion which attributes solidity to that more 

 condensed part of the head which appears to 

 the naked eye as a nucleus." Nevertheless, he 

 tells us upon the preceding page thatCassini de- 

 scribes the comets of 1665 and 1682 as being as 

 round and well defined as Jupiter, and further 

 on he writes of the comet of 1843, " On this 

 day, when viewed through a 46-inch achro- 



the square inch as now do ; consequently the 

 temperature would be four times as great as 

 it now is, and its waters would exist only as 

 vapor in its atmosphere, enveloping the body 

 and seeking shelter from the source of heat in 

 the shadow of the nucleus. The moon would 

 be in a like condition. Still, the fated worlds 

 went on into the increasing heat, and one by 

 one the forms of less refractory matter would 

 be dissipated into vapor, in the order of their 

 sensitiveness to heat, until finally all of its oxi- 

 dized matter would be vaporized, because it 

 had formerly yielded at like temperatures to 

 oxidation and therefore to vaporization, and 

 there would be left of the nucleus only those 

 forms of the metals which resisted the process 

 of oxidation with the greatest energy ; though 

 some of them, which had not before yielded to 

 oxidation, would do so now, owing to the fact 

 that the elements more ready to combine with 

 oxygen had already done so, and more oxygen 

 would therefore be free to enter into combina- 

 tion with the next form of matter that was the 

 least refractory in that respect. But when this 



