SECT. XXXVI. VARIABLE STARS. 393 



the same year, and, in March, 1574, it had entirely disappeared, 

 having exhibited a variety of tints. It is suspected, however, 

 that this star is periodically variable and identical with stars 

 which appeared in the years 945 and 1264. A more recent case 

 occurred in the year 1670, when a new star was discovered in 

 the head of the Swan, which, after becoming invisible, reappeared, 

 and, having undergone many variations in light, vanished after 

 two years, and has never since been seen. On the 28th of April, 

 1848, Mr. Hind discovered a star of the 5th magnitude in the 

 constellation Ophiuchus, which was very conspicuous to the 

 naked eye, and where he was certain no star even so bright as 

 the 9th magnitude had ever existed, nor was there any record 

 of such a star. From the time of its discovery it continued to 

 diminish till it became extinct. Its colour was ruddy, and was 

 thought to undergo remarkable changes, probably an effect of its 

 low position, as its polar distance was 102 39' 14". 



Sir John Herschel discovered very singular variations in the 

 star ?; of the constellation Argo. It is surrounded by a wonderful 

 nebula, and between the years 1677 and 1826 it varied twice 

 from the 4th to the 2nd magnitude ; but in the beginning of 

 1838 it suddenly increased in lustre, so as to be nearly as bright 

 as a Centauri. Thence it diminished, but not below the first 

 magnitude till April 1843, when it had again increased, so as to 

 surpass Can opus, and nearly equal Sinus in splendour. With 

 regard to this singular phenomenon, Sir John Herschel observes, 

 that " Temporary stars heretofore recorded have all become totally 

 extinct. Variable stars, as far as they have been carefully at- 

 tended to, have exhibited periodical and regular alternations (in 

 some degree at least) of splendour and comparative obscurity ; 

 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 ? What conclusions 

 are we to draw as to the comfort or habitability of a system de- 

 pending 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 is variable, a circum- ; 



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