HALLEY'S COMET. 



from the comet will appear four times as large as it appears at the earth at the 

 nearer extremity, it will be reduced to the magnitude of a star at the more 

 remote extremity. The vicissitudes of temperature, not to mention those of 

 light, consequent upon this change of position, will be sufficiently obvious. If 

 the earth were transported to the more remote extremity of the comet's orbit, 

 every liquid substance would become solid by congelation ; and it is extremely 

 probable that atmospheric air and other permanant gases might become liquids. 

 ) If the earth was, on the other hand, transferred to the nearer extremity of the 

 ; comet's orbit, all the liquids upon it would be converted into vapor, would form 

 permanent gases, and would either by their mixture constitute atmospheric air, 

 or would arrange themselves into strata, one above the other, according to their 

 specific gravities. All the less refractory solids would be fused, and ^ould 

 form in the cavities of the nucleus, oceans of liquid metal. 



The following observations of Dick on this comet will be read with 

 interest : 



" Soon after the middle of September, as I was taking a sweep with a two- 

 feet telescope over the northeastern quarter of the heavens, near the poiat 

 where I expected its appearance, I happened to fix my eye on this long-expected 

 visiter, which appeared very small and obscure. I immediately directed an 

 excellent three and a half feet achromatic telescope, with a diagonal eye piece, 

 magnifying about thirty-four times, to the comet, when it was distinctly seen, 

 and appeared of a considerable diameter, but still somewhat hazy and obscure. 

 I afterward applied a power of forty-five, and another of ninety-five ; but it was 

 seen most distinctly with the lower power. With ninety-five it appeared 

 extremely obscure, and nearly of the apparent size of the moon.* 



" There appeared at this time nothing like a tail, but the centra] part was 

 much more luminous than the other portions of the comet, and presented some- 

 thing like the appearance of a star of the third or fourth magnitude, surrounded 

 with a haze. In some of the views I took of this object, the luminous part, or 

 nucleus, appeared to be considerably nearer one side than another. At this 

 period, and for a week or ten days afterward, the comet was Altogether invisible 

 to the naked eye. Many subsequent observations were made and published in 

 the provincial newspapers, but which my present limits prevent me from 

 inserting. 



" After the comet became visible to the naked eye, the tail began to appear, 

 and increased in length as it approached its perihelion, and at its utmost extent 

 was estimated to be above thirty degrees in length. On the 13th of October, 

 according to the observations of Arago, a luminous sector was visible in its 

 head ; on the day following, this sector had disappeared, and a more brilliant 

 one, and of greater longitudinal extent, was formed in another place. This 

 second sector was observed on the 17th, when it appeared less bright ; and on 

 the 1 8th its weakness had decidedly increased. This comet was concealed 

 till the 21st, but on that day three distinct sectors were visible in the nebulosity. 

 On the 23d, all traces of these sectors had disappeared, the nucleus, which 

 had previously been brilliant and well defined, having become so large and 

 diffuse that the observer could scarcely believe in the reality of such a sudden / 

 and important alteration, till he satisfied himself that the appearance was not < 

 occasioned by moisture on the glasses of hifc instrument. It appears, likewise, ' 

 that one of these uiminous fans or sectors was observed by Sir J. Herschel, at 

 the Cape of Good Hope, after the comet had passed its perihelion. The nebu- 

 losity of this comet appears to have increased in magnitude as it approached 



* In viewing comets, telescopes with large apertures, and comparatively low magnifying power?, 

 should generally be used, as the faint li-lit emitted by comets, whether it be inherent or reflected, 

 will not permit the use of to high magnifying powers as may be applied to the planets. 



