Observations of the Comet of Encke. 305 



V. If the line a 6, which in all the figures passes through k, 

 the most luminous point, and K the geometric centre of gravity 

 of the whole figure, be called the axis of the comet, all that 

 part which is on the side of b may be regarded as a tail occu- 

 pying both sides of the axis. The best defined boundary was 

 always on the side of a, and the least defined, on the side of 

 b ; the former taking a parabolic curve from a towards c and c?. 

 But the point most deserving of notice, is the direction of the 

 axis in respect to the sun. Its apparent direction was deter- 

 mined four times on the 7th and 14th of December ; and the 

 apparent direction of the tail of an ordinary comet in opposition 

 to the sun being calculated, differences amounting to 100°, 

 145°, 154°, and 149°, appeared between the observed and the 

 calculated directions. Thus the direction of the diffused or 

 spreading part of the comet was always turned rather towards 

 than from the sun, offering, in this respect, an absolutely new 

 phenomenon ; the more remarkable, because the best defined 

 part of the contour, both of the envelope and of the nucleus, were 

 on the side from the sun. If we compare these observations with 

 those which have been made on other comets, Encke^ comet 

 will appear to have something in its nature different from other 

 comets, and to be, in some respects, opposed to them ; inso- 

 much that we might be disposed to name it a negative comet. 



VI. The appearance of this comet, when seen in 1825, was, 

 to the best of M. Struve's recollection, that of an almost plane- 

 tary disc of uniform light. If this recollection, grounded on 

 observations made with a 5 feet telescope of Troughton's, can 

 with propriety be compared with the observations of 1828, the 

 appearance offered by the comet on its last return, was essen- 

 tially different from that which it presented on the former 

 occasion; and if so, we may anticipate important results from 

 future observations. 



" Will/' M. Struve concludes, " the direction of the tail of 

 this comet towards the sun, and the diminution of its magni- 

 tude, on approaching that powerful luminary, justify a suppo- 

 sition, that the sun attracts to itself a portion of the mass of 

 this comet, which being thus subjected to successive diminu- 

 tions, will finally be absorbed altogether, and the comet cease 



