STARLESS OPENINGS. 143 



and agglomerative forces of the marginal grcaps.* " They 

 are parts of our starry stratum," says he, with his usua' 

 graceful animation of style, "that have experienced great 

 devastation from time." If we picture to ourselves the 

 telescopic stars lying behind one another as a starry canopy 

 spread over the vault of heaven, these starless regions in 

 Scorpio and Serpentarius may, I think, be regarded as tubes 

 through which we may look into the remotest depths of 

 space. Other stars may certainly lie in those parts where 

 the strata forming the canopy are interrupted, but these 

 are unattainable by our instruments. The aspect of fiery 

 meteors had led the ancients likewise to the idea of clefts 

 or openings (chasmatd) in the vault of heaven. These open- 

 ings were, however, only regarded as transient, whilst the 

 reason of their being luminous and fiery, instead of obscure, 

 was supposed to be owing to the translucent illuminated 

 ether which lay beyond them.f Derham and even Huygens, 

 did not appear disinclined to explain in a similar manner the 

 mild radiance of the nebulaB.J 



When we compare the stars of the first magnitude, which 

 on an average are certainly the nearest to us, with the non- 

 nebulous telescopic stars, and further, when we compare the 

 nebulous stars with unresolvable nebula?, for instance, with 

 the nebula in Andromeda, or even with the so-called pla- 

 netary nebulous vapour, a fact is made manifest to us by the 

 consideration of the varying distances and the boundlessness 

 of space, which shows the world of phenomena, and that which 

 constitutes its causal reality, to be dependent upon the pro- 

 pagation of light. The velocity of this propagation is, accord- 

 ing to Struve's most recent investigations, 166,072 geo- 

 graphical miles in a second, consequently almost a million of 

 times greater than the velocity of sound. According to the 

 measurements of Maclear, Bessel, and Struve, of the paral- 

 laxes and distances of three fixed stars of very unequal magni- 

 tudes (aCentauri, 16 Cygni, and a Lyra), a ray of light requires 



* " An opening in the heavens," William HerscLel in the Phil. Trmu. 

 for 1785, vol. Ixxv. P. I. p. 256. Le Fran^ais Lalande, in the Connaiss. 

 des Terns pour I' An VIII., p. 383. Arago, in the Annuaire, 1842, p. 425. 



f Aristot., Meteor., ii. 5, 1. Seneca, Natur. Qncest., i. 14, 2. 

 " Coelum discessisse," in Cic., de Divin , i. 43. 



J Arago, in the Annuaire, 1842, p. 429. 



