INTRODUCTION. 



19 



SIX. The length of these appendages is sometimes immense ; that of the comet of 1680 was 

 40 milhon leagues. These bodies revolve round the sun in very elliptic orbhs, some moving 

 with great velocity, others with extreme slowness, some in a direct, and others in a retrograde 

 course ; but it has been shown that their motions are regulated by the same general laws as 

 those of the planets, and the times of the revolutions of several are known. 



4. Rotation of the Sim and Planets. From the phenomena of the spots, which, by the aid 

 of a telescope, are visible on the sun's disc, we are led to the conclusion, that that body re- 

 volves from east to west on an axis, in about twenty-five days and a half. If a spot is carefully 

 watched, when first discovered on the eastern edge of the disc, it will be found to move 

 gradually toward the centre, and thence toward the western edge, until at length it entirely 

 disappears in that direction ; and in about fourteen days it is olien seen again on the eastern 

 side. That the moon, and Mercury, Venus, Mars, Jupiter, and Saturn, have each a rotation 

 from west to east is inferred in like manner from the spots that are seen to traverse their discs. 

 The moon always presents the same side to the earth, and must, therefore, revolve on her axis in 

 the same time in which she is carried round the earth by her revolution in her orbit. In the 

 remaining planets no appearances have been discovered which enable us to ascertain whether 

 or not they revolve on axes ; though from analogy it is highly probable that they do. 



The Ecliptic. 



F>. ^flpparent Annual Motion of the Sun. Zodiac. Beside the apparent daily motion of 

 the sun round the earth, he also appears to move eastward among the fixed stars. The clicle 

 which the plane of the path or orbit thus annually described, marks out on the sphere of the 

 heavens, is called the ecliptic. It passes through twelve constellations, which are called the 

 twelve signs. This has given rise to the division of the ecliptic into twelve equal parts, which 

 are also called signs, and each of wdiich of course contains 30 degrees, or one-lvv-elfth of a 

 whole circle of 360 degrees. The twelve signs are contained in a zone or belt of the starry 

 heavens, 47 degrees in breadth, called the Zodiac. The names of these constellations, wilb 

 the characters by which they are usually denoted, are as follows : 



Aries or Ram 'Y'- 

 Taurus or Bull y . 

 Gemini or Twins n. 



Spring Signs. 



Libra or Scales 

 Scnr|)io or Scorpion TT|. 

 Sagittaiius or Archer^ 



Autumn Signs. 



Cancer or Crab gs. 

 Leo or Lion 

 Virgo or Virgin VJ). 



Summer Signs. 



Capricornus or Goat \jf. ^ 

 Aquarius or Water Carrier cxx. > 

 Pisces or Fishes X. ) 



Winter .Signs. 



