Observations of the Comet ofEncke. 303 



An highly interesting and curious part of M. Struve's com- 

 munication, is the remarks with which it concludes on the 

 inferences which may be drawn from the observations in regard 

 to the physical nature of the comet. We shall not attempt to 

 shorten these remarks, lest we should do them injustice. 



I. When first seen, the comet had a diameter of between 

 two and three minutes ; yet, from its extreme faintness, was 

 scarcely visible. Now, as objects shining by their own light 

 become invisible, not from increasing faintness, but from re- 

 duction of magnitude, it follows, that Encke's comet is probably 

 a body shining only by the reflected light of the sun. 



II. On the 29th of October, the comet covered a star of the 

 9 — 10 th magnitude, which passed within 22 seconds of the 

 most luminous (and therefore the densest) part of the comet, 

 without losing any portion of its brilliancy. On the 7th of 

 November, a star was seen so situated as to be at first mistaken 

 for a nucleus shining through the nebulous matter of the 

 comet, until its motion discovered its real nature. And on the 

 same night another star was covered by the comet, and passed 

 within a very few seconds of its most luminous part, without 

 being in the least degree obscured. From these observations, 

 it appears that the comet had no solid [opaque] nucleus. 



III. In regard to the form and appearance of the comet, as 

 early as the 7th of November, a nebulous spot, more luminous 

 than the rest, could be distinguished, extending, as shewn by 

 the plate, from a to K. ( Vide Lithographic Plate, Fig. I. and 

 II.) This spot was not simply a condensation of the nebulous 

 matter towards k, the most luminous point, for it had a well- 

 defined limit at a, whilst at K the limit was not so well 

 defined as at other parts. On the 30th of November, the 

 limit of the spot and the exterior limit of the comet coin- 

 cided at a, and at this time there appeared to be at A: a nucleus, 

 with imperfectly defined limits, shining through the nebulous 

 matter in which it was enveloped. It was this point k, the 

 centre of the apparent nucleus, which was adopted throughout 



