6o THE POPULAR SCIENCE MONTHLY. 



the fourth magnitude. The temporary stars of 1572 and 1604 had 

 directed the attention of astronomers to the variableness of the light of 

 stars; and already, in 1050, Bouillaud had approximately determined 

 the period of Mira Ceti, or the star o in the constellation of the Whale. 

 Cassini, who observed sensible variations in the star of the Fox, sup- 

 posed that its period could be fixed at ten months ; but it was sought 

 for in vain in February, 1672; it did not reappear till the end of 

 March, being at that time of the sixth magnitude; then it disappeared 

 once more, and has since never been seen. 



Between the star of the Fox and the star discovered on AjDril 28, 

 1848, by Hind in Ophiuchus (or Serpentarius), 177 years elapsed. The 

 star of 1848, which was of a dark yellow or reddish color, did not ex- 

 ceed the fifth magnitude, but the variations of its light were care- 

 fully studied during the whole period of its visibility. In 1850 it was 

 hardly of the eleventh magnitude, and this magnitude it has since 

 kept. 



Here we may refer to the researches made since Cassini's time 

 into ancient writings, whether European or Chinese, which show that 

 many similar apparitions of new stars have been noted in chronicles 

 and afterward forgotten : for instance, the star of the year 125 b. c, 

 observed by Hipparchus, as we learn from Pliny ; another, which ap- 

 peared in the Emperor Hadrian's time ; the new st ar seen in the constel- 

 lation of the Eagle in the year 389, and which possessed a brilliancy 

 resembling that of Venus ; that seen in the Scorpion in the ninth cen- 

 tury; the new stars of the years 945 and 1264, both of which made 

 their appearance in very nearly the same j^art of the heavens between 

 Cepheus and Cassiopeia. 



Before we come to the two latest temporary stars, which have 

 succeeded each other in an interval often and a half years, and which 

 are worthy of a detailed description, let us briefly state the questions 

 to which these apparitions have given rise among astronomers, and 

 the hypotheses which have been oifei*ed for their solution. 



To what causes must we refer the nearly always sudden appari- 

 tions of these strange bodies, their variations of lustre, their inter- 

 mittence, as also their changes of color? Why is it that, after alter- 

 nations of great lustre and of paling, their light gradually faded 

 away, and what is the cause of their ultimate disappearance ? 



A thousand conjectures have been made in the eflfort to answer 

 this question. Among the weightiest of these, the one which com- 

 pares temporary stars to variable periodic stars must be rejected at 

 once not on the ground that these two classes of stars are absolutely 

 distinct, but because the periodicity being due, either to a movement 

 of rotation or to occultation on the one hand, or to a phenomenon 

 peculiar to the star itself on the other, the first hypothesis is clearly 

 inadmissible for the explanation of new stars, and the secT)nd is pre- 

 cisely the question to be solved. 



