72 COSMOS. 



If we compare the regions of the universe with one of tli* 

 island-studded seas of our own planet, we may imagine mat- 

 ter to be distributed in groups, either as unresolvable nebulae 

 of different ages, condensed around one or more nuclei, or as 

 already agglomerated into clusters of stars, or isolated sphe- 

 roidal bodies. The cluster of stars, to which our cosmical 

 island belongs, forms a lens-shaped, flattened stratum, detached 

 on every side, whose major axis is estimated at seven or 

 eight hundred, and its minor one at a hundred and fifty times 

 the distance of Sirius. It would appear, on the supposition 

 that the parallax of Sirius is not greater than that accurately 

 determined for the brightest star in the Centaur (0"'9128), 

 that light traverses one distance of Sirius in three years, 

 whilst it also follows from Bessel's earlier excellent Memoir* 

 on the parallax of the remarkable star 61 Cygni (0"'3483), 

 (whose considerable motion might lead to the inference of 

 great proximity), that a period of nine years and a quarter is 

 required for the transmission of light from this star to our 

 planet. Our starry stratum is a disc of inconsiderable thick- 

 ness, divided a third of its length into two branches ; it is 

 supposed that we are near this division, and nearer to the 

 region of Sirius than to the constellation Aquila, almost in 

 the middle of the stratum in the line of its thickness or minor 

 axis. 



This position of our solar system, and the form of the whole 



* See Maclear's " Results from 1839 to 1840," in the Trans, of the 

 Astronomical Soc., vol. x-ii. p. 370, on a Centauri, the probable mean 

 error being 0"'0640. For 61 Cygni, see Bessel, in Schumacher's Jahr- 

 buck, 1839, s. 47, and Schumacher's Astron. Nachr., bd. xviii. s. 401. 

 402, probable mean error, O r(> 0141. With reference to the relative 

 distances of stars of different magnitudes, how those of the third mag- 

 nitude may probably be three times more remote, and the manner 

 in which we represent to ourselves the material arrangement of the 

 starry strata, I have found the following remarkable passage in Kepler'a 

 Epitome Astronomies Copernicance, 1618, t. i. lib. 1, p. 34-39 : 

 "Sol hie noster nil aliud est quam una ex fads, nobis major et clarior 

 visa, quia propior quamfixa. Pone terram stare ad lotus, una semi- 

 diametro vice lactece, tune hcec via lactea apparebit circulus parvus, 

 vel ellipsis parva, tota declinans ad latus alterum , eritque simul uno 

 intuitu eonspicua, quce nunc non potest nisi dimidia conspici guovis 

 momenta. Itaquefixarum splicer a non tantum orbe stellarum, sed etiam 

 tirculo lactis versus nos deorsum est terminata." 



