214 Observations on Comet II. 



real, and not caused by weariness of the eye ; I only know that 

 nothing of the kind ever occurs when I am engaged in examin- 

 ing the nebula of Orion ; and on this evening any fixed star 

 which I observed continued sharp and unchanged as long as I 

 looked at it. 



This was the only occasion on which I observed either by 

 the telescope, or with the naked eye, any momentary variation 

 in the comet's appearance. Something of the kind, however, 

 appears to have been occasionally observed by others. "All of 

 us," writes my correspondent at Florence, " have remarked 

 that the light of the tail varied, and seemed at moments to dart 

 upwards in a stream from the nucleus, somewhat like an aurora 

 on a small scale." Similar to this was an appearance observed 

 at Versailles in the case of Donates Comet, but strongly and 

 vividly marked, like everything connected with that glorious 

 phenomenon. The narrator, Dr. Montucci, states that, in Sep- 

 tember 1858, he, in company with another person, saw the 

 comet suddenly fade away, tail, head, and nucleus — the nucleus 

 disappearing a few seconds after the rest. For upwards of a 

 minute (and this happened in clear weather), not the slightest 

 vestige of the comet was visible, and then " the nucleus, so to 

 say, caught fire again, and the superb tail shot out again in a 

 blaze like a sky-rocket." This whole affair occupied about five 

 minutes, and occurred five or six times in the same evening. 

 It was also observed on subsequent evenings.* A similar 

 phenomenon, as far as the disappearance 'of the tail goes, was 

 observed on July 4th (by a correspondent of the Morning 

 Herald), as occurring with the great comet of 1861. 



Such appearances are referred to also by Mr. Hind in his 

 treatise on The Comets. " There is," he says, " one singular 

 appearance in the trains of great comets which we must not 

 pass over in silence. It consists of apparent vibrations or 

 coruscations, similar to the pulsations peculiar to the Aurora 

 Borealis. These vibrations commence at the head, and appear 

 to traverse the whole length of the tail in a few seconds of 

 time. The cause was long supposed to be connected with the 

 nature of the comet itself, but Olbers pointed out that such 

 appearances could only be attributed to the effects of our own 

 atmosphere." This kind of movement is recorded as having 

 been observed in the tails of comets in 1607, 1618, 1652, and 

 1662, and, more recently, in that of 1769, and the great comet 

 of 1843. Should another remarkable comet appear, the ob- 

 servation of this phenomenon would be an important employ- 

 ment for those who observe principally with the naked eye; 

 and I would say to them, " You cannot view a comet too ear- 

 nestly, too carefully. It hangs there, apparently an established 

 * From the Comptes Rendus of the Academy of Sciences. 



