STARLESS OPENINGS. 153 



hransluc(!iit illuminated ether which lay beyond them.* Der- 

 ham, and even Iluygens, did not appear disinclined to explain 

 in a similar manner the mild radiance of the nebulae. t 



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 nebulae, for instance, with 

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

 nebulous vapor, a fact is made manifest to us by the consider- 

 ation of the varying distances and the boundlessness of space^ 

 which shows the world of phenomena, and that which con- 

 stitutes its causal reality, to be dependent upon the propaga- 

 tion of light. The velocity of this propagation is, according 

 to Struve's most recent investigations, 166,072 geographical 

 miles in a second, consequently almost a million of times 

 greater than the velocity of sound. According to the meas- 

 urements of Maclear, Bessel, and Struve, of the parallaxes 

 and distances of three fixed stars of very unequal magnitudes 

 (a Centauri, 16 Cygni, and a Lyrte), a ray of light requires 

 respectively 3, 9|, and 12 years to reach us from these three 

 bodies. In the short but memorable period between 1572 

 and 1604, from the time of Cornelius Gemma and Tycho 

 Brahe to that of Kepler, three new stars suddenly appeared 

 in Cassiopeia and Cygnus, and in the foot of Serpentarius. 

 A similar phenomenon exhibited itself at intervals in 1670, in 

 the constellation Vulpis. In recent times, even since 1837, 

 Sir John Herschel has observed, at the Cape of Good Hope, 

 the brilliant star 7] in Argo increase in splendor from the 

 second to the first magnitude. $ These events in the universe 

 belong, however, with reference to their historical reality, to 

 other periods of time than those in M'hich the phenomena of 

 light are first revealed to the inhabitants of the Earth : they 

 reach us like the voices of the past. It has been truly said, 

 that with our large and powerful telescopic instruments we 

 penetrate alike through the boundaries of time and space : we 

 measure the former through the latter, for in the course of an 



* Aristot., Meteor., ii., 5, 1. Seneca, Natnr. Qncest., i., 14, 2. " Cae- 

 lum discessisse," in Cic, ds Divin., i., 43. 



t Arago, in the Annnaire, 1842, p. 429. 



X In December, 1837, Sir John Herschel saw the star jy Argo, which 

 iill that time appeared as of the second magnitude, and Uable to no 

 change, rapidly increase till it became of the first magnitude. In Jau 

 uarV; 1838, the intensity of its light was equal to that of a Centauri. 

 According to our latest information, Maclear, in March, 1843, found it 

 as bright as Canopus; and even a Crucis looked faint by 77 Argo. 



G2 



