PORTION 01' THE COSMOS. THE SOIAR DOMAIN. 263 



to the interpretation of the appearance of the surfaces, and 

 to the gaseous envelopes of the different orbs, to the simple 

 or divided tails of comets, the ring of zodiacal light, and the 

 enigma of the phenomenon of meteoric asteroids, almost 

 all the results of observation are susceptible of reduction to 

 numerical relations, and all present themselves as conse- 

 quences of assumptions admitting of being brought to the 

 test of strict demonstration. 



Such demonstration does not fall within the scope of this 

 " Sketch of a Physical Description of the Universe," but the 

 methodical presentation of the numerical results in a brief 

 and collected form does belong to the plan of such a sketch, 

 These results constitute the rich inheritance which, evermore 

 growing by continual accession, is handed down from one 

 century to another. A table containing the numerical ele- 

 ments of the planets (showing in the case of each planet its 

 mean distance from the sun, its period of revolution, excen- 

 tricity of orbit, inclination to the ecliptic, diameter, mass, 

 and density), gives in an exceedingly small space the 

 standard of knowledge, or the intellectual height in this 

 respect, to which the age has attained. If we throw our- 

 selves back in imagination for a moment into the times of 

 classical antiquity, and figure to ourselves Philolaus the Pytha- 

 gorean (the instructor of Plato), Aristarchus of Samos, or Hip- 

 parchus, in possession either of a sheet with such a table of 

 numbers, or of a graphical representation of the planetary 

 orbits such as is given in our briefest elementary works, we 

 could only compare the astonishment of these men, the 

 heroes of the earlier more limited knowlege, to that of Eras- 

 tosthenes, Strabo, or Ptolemy, if one of our maps of the 



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