THE COAL-SACKS. 51 



(1689) should have mistaken Acosta's ''manchas negras'' for 

 the luminous Magellanic Clouds.* 



Richaud, moreover, like the earliest pilots, speaks of the 

 Coal-sacks in the plural, mentioning two, of which the large 

 one was situated in the constellation of the Cross, and an- 

 other in Charles's Oak ; the latter, according to other descrip- 

 tions, was subdivided into two distinct specks. These were 

 described 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.! 

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

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

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

 stellation, I applied for information to Sir John Herschel and 

 to Riimker, the director of the Observatory at Hamburgh, 

 who had been in far more southern latitudes than myself. 

 Notwithstanding their endeavors, they were equally unsuc- 

 cessful in discovering any thing that could be compared for 

 definiteness of outline and intensity of blackness with the 

 Coal-sack in the Cross. Sir John Herschel is of opinion that 

 we can not 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 fS and 

 y Trianguli,$ between rj and 6 Argus, and more especially 

 the barren portion of the Milky Way in the Northern heav- 

 ens, between e, a, and y Cygni.^ 



The longest known Black Speck 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 magni 

 tude, together with a large number of telescopic stars, vary 

 ing from the 11th to the 13th magnitudes. A small group 

 of 40 stars lies nearly in the center. ll The paucity of stars, 

 and the contrast with the magnificent effulgence of the neigh- 



* M^m. de V Acad, des Sciences dep. 1666 jusqu'a 1699, t. vii., partie 2 

 (Paris, 1729), p. 206. 



t Letter to Olbers from St. Catharina (January, 1804), in Zach's 

 Monatl. Correspondenz zur Beford. der Erd- nnd Himmels-Kunde, bd. 

 X., p. 240. See, on Feuillee's observation and rough sketch of the black 

 spot in the Southern Cross, Zach, Op. cit., bd. xv., 1807, p. 388-391. 



% Observ. at the Cape, pi. xiii. § Outlines of Astronomy, p. 531, 



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

 and clusters. (Compare Dunlop in the Philos. Transact, for 1828, p. 

 149, and No. 272 of his Catalogue.) 



