PORTION OP THE COSMOS. COMETS. 405 



comet, or may mingle with the ancient cosmical matter 

 which has not been condensed either into celestial bodies or 

 into the ring which forms our Zodiacal Light. We see 

 material particles disappear, as it were, before our eyes, and 

 can hardly conjecture where they reassemble. Now, how- 

 ever probable may be the condensation in the neighbour- 

 hood of the central body of our system of a gaseous fluid 

 filling space, yet in comets, whose nucleus, according to 

 Yalz, becomes small in the vicinity of the Sun, we cannot well 

 imagine to ourselves that this effect is caused by the sur- 

 rounding fluid being there more dense, and thus pressing 

 upon and contracting a vesicular nebulous envelope ( 667 ). If, 

 in the emanations of comets, the outlines of the light- 

 reflecting nebulosity are usually very little defined, it is the 

 more striking, and the more instructive in respect to the 

 molecular state of the body, to remark that, in particular 

 cases and individuals (for example, in Halley's comet, seen at 

 the end of January 1836 at the Cape of Good Hope), there has 

 been observed in the parabolic front part of the comet such 

 a well-marked and definite outline, as we hardly ever see in 

 the piled up clouds or cumuli of our atmosphere. The 

 illustrious observer at the Cape compared the unusual ap- 

 pearance, indicative of the strength of the mutual attraction 

 of the particles, to an alabaster vessel strongly illuminated 

 from within (a*). 



Since the appearance of the first volume of my work, an 

 occurrence has presented itself among the bodies of which 

 we are treating, the mere possibility of which could scarcely 

 have been anticipated. Biela's comet, (an interior comet 

 of short period of revolution, 6f years), parted asunder 

 and formed two comets, similar in form though unequal in 



