MILKY WAY. 201 



and therefore near Cassiopeia, (from which constellation we 

 began our description of the Milky Way) towards Ursa Minor 

 and the pole. 



From the extraordinary advancement which the applica- 

 tion of large telescopes has gradually effected in our know- 

 ledge of the sidereal contents and of the differences in the con- 

 centration of light observable in individual portions of the 

 Milky Way, views of merely optical projection have been re- 

 placed by others referring rather to physical conformation. 

 Thomas Wright of Durham, 92 Kant, Lambert, and at first 

 also Sir William Herschel, were disposed to consider the form 

 of the Milky Way, and the apparent accumulation of the stars 

 within this zone, as a consequence of the flattened form and 

 unequal dimensions of the world-island (starry stratum,) in 

 which our solar system is included. The hypothesis of the 

 uniform magnitude and distribution of the fixed stars has- 

 recently been attacked on many sides. The bold and gifted 

 investigator of the heavens, Wm. Herschel, in his last works, 

 expressed himself strongly in favour of the assumption of an 

 annulus of stars ; a view which he had contested in the talented 

 treatise he composed in 1 784. The most recent observations 

 have favoured the hypothesis of a system of separate concentric 

 rings. The thickness of these rings seems very unequal ; and 

 the different strata whose combined stronger or fainter light 

 we receive, are undoubtedly situated at very different altitudes, 



18 De Morgan has given an extract of the extremely rare 

 work of Thomas Wright of Durham, ( Theory of the Universe, 

 London, 1750,) p. 241 in the Philos. Magazine, ser. iii. 

 no. 32. Thomas Wright, to whose researches the attention 

 of astronomers has been so permanently directed since the 

 beginning of the present century, through the ingenious 

 speculations of Kant and William Herschel, observed only 

 with a reflector of one foot focal length. 



93 Pfaff, in Will. HerscheV s sdmmtl. Schriften, bd. i. (1826) 

 s. 78-81 ; Struve, Etudes stell, pp. 35-44. 



