THE SOLAR REGION. 53 



However wonderful are the improvements made in optical 

 instruments within scarcely sixty years, we are at the same 

 time too well acquainted with the difficulties of their con- 

 struction to indulge in the bold and even unlicensed antici- 

 pations so ardently cherished by the intellectual Hooke from 

 1663 to 1665.* Moderation in the expectations entertained 

 will be the most likely to lead to their fulfillment. Each 

 succeeding generation has reaped the noblest and most ex- 

 alted results from the triumphs of free intellect in the differ- 

 ent stages to which art has gradually exalted itself. Without 

 attempting to express in definite numbers the distances to 

 which the space-penetrating powers of telescopic vision may 

 already reach, and without attaching much confidence to 

 such numbers, the knowledge of the velocity of light yet pro- 

 claims that the appearance of the remotest star the light- 

 generating process on its surface is the " most ancient sens- 

 uous evidence of the existence of matter."! 



j3. THE SOLAR REGION. 



PLANETS AND THEIR SATELLITES. COMETS. RING OF THE 



ZODIACAL LIGHT. SWARMS OF METEOR-ASTEROIDS. 



ON passing, in the Uranological portion of the physical 

 description of the universe, from the heaven of the fixed stars 

 to our solar and planetary system, we descend from the great 

 and universal to the relatively small and special. The do- 

 main of the Sun is the domain of one individual fixed star 

 among the millions revealed to us in the firmament by tel- 

 escopic aid the limited space in which very various cosmical 

 bodies, in obedience to the direct attraction of a central body, 

 revolve around it in more or less extended orbits, whether 

 they are isolated or -encircled by other bodies similar to them- 

 selves. Among the stellar bodies whose arrangement we 

 have endeavored to consider in the sidereal portion of the 

 Uranology, there is, indeed, a class of those millions of tele- 

 scopic fixed stars double stars which exhibit special, bi 

 nary, or multiple systems ; but notwithstanding the analogy 

 presented by the forces by which they are impelled, they yet 

 differ in their natural character from our solar system. In 



* Lettre de Mr. Hooke d M. Auzont, hi the M&m. de V Acadimie, 

 1666-1699, torn, vii., partie ii. f p. 30, 73. \ Cosmos, vol. i., p. 154. 



