of the ancients, and fancy Philolaus the Pythagorean, the 

 instructor of Plato, Aristarchus of Samos, or Hipparchus, in 

 possession of such a numerical table, or of a graphic repre- 

 sentation of the orbits of the planets, such as is given in our 

 most epitomized manuals; there is scarcely anything to 

 which we could compare the admiration and surprise of 

 these men, the heroes of the early and limited knowledge 

 of that age, excepting, perhaps, that which might have been 

 experienced by Eratosthenes, Strabo, and Claudius Ptolemy, 

 could they have seen one of our maps of the world, on 

 Mercator's projection, not above a few inches in length and 

 breadth. 



The return of comets in closed elliptical orbits, as a conse- 

 quence of the attractive force of the central body, indicates 

 the limits of the solar region. As, however, we are as yet 

 ignorant whether comets may not some day appear in which 

 the major axis may prove to be larger than any that have as 

 yet been observed and calculated, these bodies must be 

 regarded as indicating, in their aphelia, merely the limits to 

 which the solar regions must at least extend. Hence we may 

 characterize the solar system by the visible and measurable 

 results of peculiar operating central forces, and by the cos- 

 mical bodies (planets and comets) which rotate round the 

 Sun in closed orbits, and are intimately connected with it. 

 The considerations which at present engage our attention, do 

 not embrace a notice of the attraction which the Sun may 

 exert on other suns (or fixed stars) lying beyond the limits of 

 these re-appearing cosmical bodies. 



According to the state of our knowledge at the close of this 

 half of the nineteenth century, the solar region includes the 

 following bodies, arranging the planets according to their 

 respective distances from the central body: 



