H2 ON COMETS. 



structure and convolutions of the jets issuing from it. 

 From this time, to its final disappearance, the violence 

 of action gradually calmed down, while the comet it- 

 self went southwards, and at length vanished from our 

 horizon. 



(46.) An idea of the actual dimensions of this comet 

 may be formed from the measurements taken by Professor 

 Bond on the 2d October, which, combined with the dis- 

 tance of the comets from the earth at that date afford 

 the following results, viz. : 



Miles. 



Diameter of the bright internal pellet or nucleus, . 1,600 



Distance from its centre to the summit of the 



first envelope, .... 7, 500 



Distance to that of the second envelope, . . 13,200 



Breadth of the brightest part of the tail where it 

 seemed (to the naked eye) to issue from the 

 comet, ..... 90,000 



to which it may be added that the actual length of the 

 tail, when at its greatest development, could not have 

 been less than 30 millions of miles, and those of the 

 faint streaks or secondary tails 34 or 35 millions. 



(47.) The comet of 1861, which burst suddenly on us in 

 its full splendour on the 30th of June in that year (though 

 it had been seen for seven weeks before in the southern 

 hemisphere), was considered by those who saw it at its 

 first appearance to surpass in brightness even that of 

 1858, and was remarkable for the extreme breadth and 

 diffusion of its tail when first seen, arising from the cir- 

 cumstance of the earth having been then situated nearly 

 in its prolongation. Indeed, it is not impossible that on 

 that day we actually traversed some portion of it, our 



