894 SPECIAL RESULTS IN THE URANOLOG1CAL 



III. 



COMETS. 



IN the solar domain, the comets which Xenocrates and 

 Theon of Alexandria termed " Clouds of Light/' and 

 which, according to an ancient belief, handed down from 

 the Chaldeans, were said by Apollonius the Myndian to 

 ' ' ascend periodically from remote distance on long (regu- 

 lated) paths" although subject to the attracting force of 

 the central body of our system, form, nevertheless, a pecu- 

 liar and distinct group. They are distinguished from pla- 

 netary bodies properly so called, and meaning thereby both 

 primary planets and satellites, not merely by the great 

 excentricity of their orbits, but also by what is still 

 more material their cutting through or intersecting the 

 orbits of the planets ; and they present, moreover, a 

 variability of form a mutability of outline which, in 

 some individuals, (for example, in Klinkenberg's comet 

 of 1744 so accurately described by Hensius, and in 

 Halley's comet on its last appearance in 1835), becomes 

 sensible even in the course of a few hours. Before Encke 

 had enriched our knowledge of the solar system with comets 

 of short period, called interior comets because their orbits 

 are included within some of the planetary orbits, dogmatic 



