T4 SCENERY IN A PATCH 







from the sun, it was called the beard, being only termed the 

 tail when seen following the nucleus as the sun is approach- 

 ed. This distinction has disappeared from all modern 

 astronomical works, and the latter name is given to the ap- 

 pendage, whatever its apparent position. Neither this 

 luminous attendant, the tail, nor the nucleus, are now con- 

 sidered essential cometary elements, but all bodies are 

 classed as comets which have a motion of their own, and 

 describe orbits of an extremely elongated form. There 

 are several plain points of difference between comets and 

 planets. The planets move in the same direction from 

 west to east, which is astronomically called direct motion ; 

 but the movements of comets are often from east to west, or 

 retrograde. The orbits of all the planets are confined to a 

 zone of no great breadth on either side of the ecliptic ; but 

 the paths of comets cut the ecliptic in every direction, some 

 being even perpendicular to it, traversing the heavens in all 

 parts. The contrast is striking likewise between the forms 

 of their respective orbits. A hoop will with no great inac- 

 curacy represent the courses of the planets, but the cometary 

 paths are immensely elongated ellipses, their breadth bear- 

 ing no proportion to their length. Only one end of the 

 ellipse lies within the visible limits of the solar system, in 

 the case of the great majority of these bodies. They only 

 visit our gaze therefore during one part of their course, and 

 that a very small part, traveling during the rest of their 

 journey far beyond the range of the most distant planet, 

 into spaces inaccessible to our sight. The circumstances of 

 their motions plainly distinguish them from the planets, 

 fixed stars, and nebulae. Planetary configuration is also 

 uniformly globular, but the external appearances of comets 

 exhibit great diversities of form, from that of an irregular 

 wisp of cloud to a simple spherical luminosity, or a strongly 

 defined scimitar-shaped aspect. 



