148 COSMOS. 



whose practical solution must be left to future ages.* When 

 we compare our Sun with the other fixed stars, that is, with oth 

 er self-luminous Suns in the lenticular starry stratum of which 

 our system forms a part, we find, at least in the case of some, 

 that channels are opened to us, which may lead, at all events, 

 to an approximate and limited knowledge of their relative 

 distances, volumes, and masses, and of the velocities of their 

 translatory motion. If we assume the distance of Uranus 

 from the Sun to be nineteen times that of the Earth, that is 

 to say, nineteen times as great as that of the Sun from the 

 Earth, the central body of our planetary system will be 11, 900 

 times the distance of Uranus from the star a in the constella- 

 tion Centaur, almost 31,300 from 61 Cygni, and 41,600 from 

 Vega in the constellation Lyra. The comparison of the vol- 

 ume of the Sun with that of the fixed stars of the first mag- 

 nitude is dependent upon the apparent diameter of the latter 

 bodies — an extremely uncertain optical element. If even we 

 assume, with Herschel, that the apparent diameter of Arctu- 

 rus is only a tenth part of a second, it still follows that the 

 true diameter of this star is eleven times greater than that of 

 the Sun.f The distance of the star 61 Cygni, made known 

 by Bessel, has led approximately to a knowledge of the quan- 

 tity of matter contained in this body as a double star. Not- 

 withstanding that, since Bradley's observations, the portion 

 of the apparent orbit traversed by this star is not sufficiently 

 great to admit of our arriving with perfect exactness at the 

 true orbit and the major axis of this star, it has been conjec- 

 tured with much probability by the great Konigsberg astron- 

 omer,t " that the mass of this double star can not be very con- 

 siderably larger or smaller than half of the mass of the Sun." 

 This result is from actual measurement. The analogies de- 

 duced from the relatively larger mass of those planets in our 

 solar system that are attended by satellites, and from the fact 

 that Struve has discovered six times more double stars among 



* Bessel, Untersuchung. des Theils der planetaHschen Storungen, 

 welcke aus der Betcegumg der Sonne entsieken (An Investigation of the 

 portion of the Planetary Disturbances depending on the Motion of the 

 Sun) in Abh. der Berl. Akad. der Wissensch., 1824 (Mathem. Classe), 

 8. 2-6. The question has been raised by John Tobias Mayer, in Com- 

 ment. Soc. Reg. Gotting., 1804-1808, vol. xvi., p. 31-68. 



t Fkilos. Trans, for 1803, p. 225. Arago, in the Annuaire, 1842, p. 

 375. In order to obtain a clearer idea of the distances ascribed in a 

 rather earlier part of the text to the fixed stars, let us assume that the 

 Earth is a distance of one foot from the Sun; Uranus is then 19 feet, 

 and Vega Lyrae is 158 geographical miles from it. 



X Bessel, in Schum., Jahrb., 1839, s. 53. 



