THE HERSCHELS AND THE STAR-DEPTHS. II 



that the brightness of the Milky Way arises only from 

 stars ; and that their compression increases in propor- 

 tion to the brightness of the Milky Way. We may, 

 indeed, partly ascribe the increase both of brightness 

 and of apparent compression, to a greater depth of the 

 space which contains these stars ; but this will equally 

 tend to show their clustering condition ; for, since the 

 increase of brightness is gradual, the space containing 

 the clustering stars must tend to a spherical form, if 

 the gradual increase of brightness is to be explained by 

 the situation of the stars.' 



But we cannot rightly understand either the theory 

 which Sir W. Herschel thus abandoned,* or that by 

 which it was replaced, without considering his researches 

 into objects quite different from the fixed stars. 



In ancient times astronomers had noticed five spots 

 on the heavens where a cloudy sort of light could 

 be recognised. These spots they had called < cloudy 

 stars.' But not very long after, the invention of the 

 telescope, several more of these star-cloudlets began to 

 be recognised. Lacaille discovered forty-five in the 



* The eminent German astronomer, Struve, thus writes respect- 

 ing Herschel's change of view : ' Kemarquons d'abord que, des 

 1802, il n'est plus question de la figure de la Voie Lactee dans les 

 recherches de Herschel. Elle n'est plus une strate limitee, car elle est 

 insondable, et il devient impossible d'en embrasser la totalite.' And again, 

 ' Nous parvenons done au resultat, peut-etre inattendu, mais incontest- 

 able, que le systeme de Herschel, enonce en 1785, sur 1'arrangement 

 de la Voie Lactee, s'ecroule de toutes parts, d'apres les recherches 

 ulterieures de 1'auteur ; et qiie Herschel luimeme Va entierement aban- 

 donne.' Yet an assertion to this effect, made by the present writer in 

 the presence of the Eoyal Astronomical Society, two years since, was 

 received with obvious signs of incredulity. 



