THE COAL-SACKS. 347 



in Charles' Oak ; the latter, according to other descriptions, 

 was subdivided into two distinct specks) These were de- 

 scribed by Feuillee, in the early part of the eighteenth 

 century, and by Horner (in a letter to Olbers, written from 

 Brazil in 1804), as undefined, and having confused outlines. 9 * 

 I was unable during my residence in Peru to discover any- 

 thing definite as to the Coal-sacks in Charles' Oak ; and as 

 I was disposed to ascribe this to the low position of the 

 constellation, I applied for information to Sir John Her- 

 schel and to Rumker, the Director of the Observatory at 

 Hamburgh, who had been in far more Southern latitudes 

 .than myself. Notwithstanding their endeavours, they were 

 equally unsuccessful in discovering anything that could be 

 compared for definiteness of outline and intensity of black- 

 ness with the Coal-sack in the Cross. Sir John Herschel is 

 of opinion that we cannot speak of a plurality of Coal-sacks, 

 unless we would include under that head every ill -defined 

 and darker portion of the heavens, as the regions between 

 a Centauri and /5 and 7 Trianguli, 95 between TJ and Argus, 

 and more especially the barren portion of the Milky Way in 

 the Northern heaveDs, between e, a, and 7 Cygni. 96 



The longest known Black A$/JC& in the Southern Cross, 

 and the one which is also the most striking as seen by the 

 naked eye, is of a pear-like shape, and lies on the eastern side 

 of that constellation, in 8 long, and 5 lat. This large space 

 presents one visible star of the 6th to the 7th magnitude, toge- 



94 Letter to Olbers from St. Catharina (January, 1804), 

 in Zach's Monatl. Correspondent zur Beford. der Erd-und 

 Himmels-Kunde, Bd. x. p. 240. See, on Feuillee's obser- 

 vation and rough sketch of the Black spot in the Southern 

 Cross, Zach, Op. cit. Bd. xv. 1807, pp. 388-391. 



95 Observ. at the Cape, pi. xiii. 



ss Outlines of Astronomy, p. 531. 



