66 The Earth in the Comet's Tail. 



The want of entire continuity in these external streams 

 would form no argument against their cometary character, even 

 had it not been established by observation at two distant 

 stations. The interruption might be only apparent, the result 

 of the position of the nucleus in the bright midsummer twilight 

 of the north horizon ; but if real it would not be unprecedented. 

 In the very curious comet of alternating light in June and 

 July, I860, one of the two sides of the tail was, towards the 

 latter part of its appearance, separated from the head ; and in 

 that of 1843, so remarkable for its visibility close to the sun at. 

 noon-day, the splendid tail which had been darted out to such 

 an amazing length had at one time no connection, visible to the 

 naked eye, with the pale and seemingly exhausted nucleus. 

 And so in the case of those "anomalous tails," those most 

 inexplicable pencils of light, which are occasionally directed 

 from the nucleus towards the sun, two instances are on record 

 (in 1824 and 1845) in which they contained a fainter interval. 



Admitting the probability of our passage through the tail, 

 it cannot be thought surprising that there should have been at 

 the time so little sensible indication of its presence. Whatever 

 may be the nature of that wholly unknown material, there can 

 be no question of its extreme and almost inconceivable atte- 

 nuation. The air we breathe may be as dense in comparison 

 with it, as water or even earth in comparison with air. The 

 minutest stars have been frequently seen through thousands of 

 miles of it, and it even ceases to be amenable to the all-con- 

 trolling force of gravitation ; so that Newton considered that 

 the tail of a great comet might be compressed into the bulk of 

 a single cubic inch before it would equal the density of our 

 atmosphere, and Sir J. Herschel supposes that it may not 

 contain more than a few pounds or even ounces of matter. It 

 would, therefore, be highly improbable that there should be a 

 sufficient quantity of it in the immediate vicinity of any one 

 place of observation to render its presence manifest. Distance 

 alone, by bringing its particles into more apparent concentration, 

 could give it density enough to become perceptible, just as the 

 same cause converts the unsubstantial and semi-transparent 

 mist into the massive and ponderous-looking cloud. It was a 

 more significant fact, and one which may not be generally 

 known, that no electric or magnetic effect whatever was percep- 

 tible during its passage j* for such influences have been strongly 

 suspected in cometary phenomena, and might act independently 

 of any material admixture. We have certainly gained very 

 little information, and less, perhaps, than might have been 



* Some lofty cirri, however, the next morning, had a singularly wild and 

 electrical aspect ; and the Greenwich instruments showed a strong change the 

 following night. 



