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THE ILLINOIS PARMER. 



147 



twenty-first of April, fifteen hundred and 

 fifty-six. Thus its period is about two hundred 

 and ninety-two years. Another appeared in 

 fifteen hundred and fifty-two,and again in sixteen 

 hundred and sixty-one, having thus a period of 

 about one hundred and twenty-nine years. The 

 return of that comet should have been in seven- 

 teen hundred and ninety. In that year three 

 comets made their appearance, but neither of 

 them resembled the one of sixteen hundred and 

 sixty-one. 



While the periods of most of the comets ex- 

 amined are comparatively short, those of others 

 have been ascertained to extend to many thou- 

 sand years. The great comet of eighteen bnndred 

 and eleven remained visible for upwards of two 

 months, and was considered one of the most 

 brilliant of modern times. After a careful in- 

 vestigation, M. Argelander fixes its period of 

 reyoliition at two thousand eight hundred and 

 eighty-eight years. The periodic time of the 

 retnrn of the comet of eighteen hundred and 

 seven was fixed by Bessel at one thousand five 

 hundred and forty-eight years. 



A comet, denominated Encke's comet, ap- 

 peared in eighteen hundred and eighteen, and 

 Eucke's observations upon it enabled him to 

 identify it with the one described by Messieurs 

 Michier and Messien in seventeen hundred and 

 ninety-five by Miss Herscbel, and the one in 

 eighteen hundred and five. 



Encke predicted its re-appearance is eighteen 

 bnndred and twenty-two, and his prediction was 

 realized by its being discovered on the second 

 of June of that year, by Thomas Brisltire; and 

 its return was noticed again in eighteen hundred 

 and twenty-five and eighteen hundred and 

 twenty eight, and attracted much attention 

 from the astronomers of that day. 



Another comet was discovered by Bella on 

 the twenty seventh of February, eighteen 

 hundred and twenty six, which revolves around 

 the sun in about six years and seven tenths. Its 

 return in eighteen hundred and forty six at- 

 tracted a good deal of attention, on account of 

 it having been discovered, by Lieut. Maury, of 

 the Washington Observatory, that what bad 

 hitherto appeared as a single body was aetnally 

 composed of two distinct and separate comets. 

 In the same year one of the comets which is now 

 visible was supposed to be identical with -the 

 third comet of eighteen hundred and forty six, 

 discovered by Brorsen, and which is now the 

 second which has made its appearance this year; 

 its retnrn perihelion is calcnlated to be on the 

 twenty fifth of June — and as the first one 

 is now in Annges, and receding from the sun, 

 the second (or Brorson's comet) is in Persens, 

 and is now visible in the northwestern part of 

 the heavens, and will be during the whole of 

 May. 



All the comets that have heretofore been ob- 

 served aave made their progress through very 

 different parts of the solar system; twenty four 

 have passed within the orbit of Mercurj , forty 

 seven within that of Venus, fifty eight within 

 that of the earth, seventy three within that of 

 Mars, and the whole within that of Jupiter. 

 Of s hundred oomets, or thereabonts, meiiti(»f|d 



hj Lalande, abont one half have moved from 

 ) -west to east, in the same direction as the planets, 

 And half in the opposite direction. 



Although the superstitious fear of comets, as 

 portending harm to the inhabitants of Uie earth, 

 has vanished before the light of philosophy, 

 ' there are still a few remaining who ent^tafa 

 ^ ■ fears of a collision with some of the comets that 

 might cross the earth's path. Ithae often been 

 predicted that that sad calamity would ulti- 

 mately take place. It Will be recollected that 

 no longer ago than eighte^i hundred and thirty 

 two it was predicted that the comet of that year 

 would cross the earth's track, and great fears 

 were entertained of -a collision. Bat there is no 

 evidence that such a collision evAr did happen, 

 either with the earth or with any other planet; 

 and there is no tn)rrect means of so calculating 

 the place of a -comet as to be able to say with 

 certainty that on a given day it will crOM the 

 orbit of a planet. The motion of the earth ki 

 its orbit is, in round numbers, more than a iiH>- 

 lion and a half miles in a day, and as Ci^iraalt, 

 with all his care, did not come nearer tfce truth 

 than nineteen days, in regard to the return of 

 Halley's comet, and his followers, with ail the 

 additional light they possessed, could cot come 

 nearer than nine days of its re-appearance at 

 the point nearest the son, on its last return, in 

 eighteen hundred and thirty five, and this comet 

 will net return again till the earth wonki in its 

 rapid course around the snn, be within nine days 

 far enough removed from the influence of the 

 comet to be out of the way of all harm. Pro- 

 fessor 0. M. Mitchell, who is eminently dis- 

 tinguished for his learning and scientific attain- 

 ments, makes use of the following language npon 

 this subject. He says: "It is aseless to spec- 

 ulate with reference to the probable consequences 

 of a collision, which there is scarcely one chance 

 in millions can ever occur. Science has as yet 

 discovered no guarantee for any plaviet against 

 the probable shock of a comet; but an examin- 

 ation of the adjustments of our system, and 

 those of Jupiter and Saturn, won id seem to in- 

 dicate to ns, that in all past tir^ae qo derange- 

 ment has ever occurred from such a cause." 

 We will dismiss this subject.^ by giving Pro- 

 fessor Arago's division of the comets. He 

 divides them into three claries, with reference to 

 their physical constitntio'^. He thinks theyu)0- 

 casionally appear round and with well defined 

 planetary discs, showir^g them to be solid opaque 

 bodies, in all r^pe^ts resembling planets and 

 only differing from them in the great eccentric- 

 ity of their orbit. ^ ^ second class of comets 

 comprehends th' jge in which there is a nuclens, 

 but devoid of^ opacity, permitting the light to 

 penetrate throng], even that portion which may 

 probably b^ golid. The third class, and that by 

 far the most nnmerous, comprehends those 

 conaets ieslitote entirely of solid nucleus, con- 

 sisting^ of matter so attenuated as to eompare 

 '"*'* nothing of which we have any knowledge 

 on the' earth's surfaee. The comets named 

 ^jtncke and Beila apx>ear to belong to this class, 

 and even Halley's comet, according to the opin- 

 { ion of Sir John Hersehel, at its last retnn, 

 appeared to belong to this dasi also. 



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