424: VARIABLE STARS. [SECT, xxxvir. 



three hours and a half more regains its brightness, going 

 through all these vicissitudes in two days, twenty hours, 

 and forty-eight minutes, a Cassiopeiae is also periodical, 

 accomplishing its changes in 225 days. The period of the 

 star 34 Cygni is 18 years. Sir John Herschel has discovered 

 very singular variations in the star 77 of the constellation 

 Argo. It is surrounded by a wonderful nebula, and has 

 continually and irregularly varied in lustre since 1677. 

 From having been of the fourth magnitude, it went through 

 many fluctuations, till it became as bright as Arcturus, and 

 even attained to the splendour of Sirius in 1838, when it 

 suddenly decreased. Sir John Herschel observes, with 

 regard to that singular phenomenon, that "Temporary 

 stars heretofore recorded have all become totally extinct. 

 Variable stars, so far as they have been carefully attended 

 to, have exhibited periodical and regular alternations (in 

 some degree at least) of splendour and comparative ob-. 

 scurity; but here we have a star fitfully variable to an 

 astonishing extent, and whose fluctuations are spread over 

 centuries, apparently in no settled period and in no regular 

 progression. What origin can we ascribe to these sudden 

 flashes and relapses 1 What conclusions are we to draw as 

 to the comfort or habitability of a system depending for its 

 supply of light and heat on so variable a source? Its 

 future career will be a subject of high physical interest. To 

 this account I will only add, that in the beginning of 1838 

 the brightness of this star was so great as materially to 

 interfere with the observations of that part of the nebula 

 surrounding it." Sir John has also discovered that a 

 Orionis may now be classed among the variable and 

 periodic stars a circumstance the more remarkable, as it 

 is one of the conspicuous stars of our hemisphere, and 

 yet its changes had never been remarked. The inferences 

 Sir John draws from the phenomena of variable stars are 

 too interesting not to be given in his own words. "A 

 periodic change existing to so great an extent in so large 



