144 COSMOS. 



tespectively 3, 9j, 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 Cas- 

 siopea and Cygnus, and in the foot of Serpentarius. A simi- 

 lar 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 77 in Argo increase in splendour 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 which 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 oui- large and powerful telescopic instruments we pene- 

 trate alike through the boundaries of time and space : we mea- 

 sure the former through the latter, for in the course of an hour 

 a ray of light traverses over a space of 592 millions of miles. 

 Whilst, according to the theogony of Hesiod, the dimensions 

 of the universe were supposed to be expressed by the time 

 occupied by bodies in falling to the ground (" the brazen 

 anvil was not more than nine days and nine nights in foiling 

 from heaven to earth,") the elder Herschel was of opinionf 

 that light required almost two millions of years to pass to 

 the Earth from the remotest luminous vapour reached by his 

 40 foot reflector. Much, therefore, has vanished long before 

 it is rendered visible to us much that we see was once dif- 

 ferently arranged from what it now appears. The aspect of 

 the starry heavens presents us with the spectacle of that 



* In December, 1837, Sir John Herschel saw the star r, Argo, which 

 till that time appeared as of the second magnitude, and liable to no 

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

 January, 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 Crucis looked faint by r, Argo. 



f " Hence it follows that the rays of light of the remotest nebulse must 

 have been almost two millions of years on their way, and that conse- 

 quently, so many years ago, this object must already have had an 

 existence in the sidereal heaven, in order to send out those rays by which 

 we now perceive it." William Herschel, in the Phil. Trans, for 1802, 

 p. 498. John Herschel, Astron. 590. Arago, in the Annuaire, 1842, 

 pp. 334, 359, and 382-385. 



