348 COSMOS. 



tlier with a large number of telescopic stars, varying from the 

 llth to the ] 3th magnitudes. A small group of 40 stars lies 

 nearly in the centre. 97 The paucity of stars and the con- 

 trast with the magnificent effulgence of the neighbouring 

 heavens, are assigned as the causes of the remarkable black- 

 ness of this portion of the firmament. This opinion, which 

 has been generally maintained since Lacaille's time, 98 has 

 been especially confirmed by the "gauges" and " sweeps " 

 made round the region where the Milky Way appears as if 

 covered by a black cloud. The Coal-bag yielded from 

 seven to nine telescopic stars for every sweep, but never 

 an entirely blank field ; while in a field of equal size the. 

 margins presented from 120 to 200 stars. This mode of 

 explanation, which ascribes the darkness to contrast alone, 

 did not, although perhaps incorrectly, appear quite satis- 

 factory to me while I was in a tropical region, and re- 

 mained under the vivid impression produced on my mind 

 by the aspect of the Southern heavens. William Herschel's 

 considerations on wholly starless regions in Scorpio and 

 Serpentarius, and which he has termed " openings in the 



97 Observ. at the Cape, p. 384, No. 3407, of the catalogue 

 of nebula? and clusters. (Compare Dun! op in the Philos. 

 Transact, for 1828, p. 149, and No. 272 of his Catalogue.) 



98 " Cette apparence d'uii noir fonce dans la par tie orien- 

 tale de la Croix du Sud, qui frappe la vue de tous ceux qui 

 regardent le ciel austral, est causee par la vivacite de la 

 blancheur de la voie lactee qui renferme 1'espace noir et 

 1'entoure de tous cotes." "The appearance of deep black in 

 the eastern portion of the Southern Cross, which strikes all 

 who observe the heavens in those regions, is owing to the 

 intensity of the whiteness of the Milky Way surrounding the 

 black space on every side." Lacaille, in the Mem. de lAcad, 

 des Sciences, annee 1755 (Paris, 1761), p. 199. 



