﻿NATURE OF THE TEMPORARY STAR OF 1572. 319 



principle just illustrated, deduct from the time of revolution of the ring, that required 

 by the light to pass over a portion of the sine of the arc through which the star has 

 advanced. We should then find its apparitions occurring at still decreasing intervals, 

 viz., 9.867 9.633 and 9.500 



The following table exhibits the periods of the star for each of its terms of invisi- 

 bility through its whole orbit, beginning at the point B, and following the letters in 

 their natural order : 



10. + .500 = 10.500 



10. + .867 — .500 ££ 10.367 



10. + 1. — .867 = 10.133 



lO. — .133 == 9.867 



10. — .367 = 9.633 



10. — .500 = 9.500 



10. — .500 = 9.500 



10. — .367 = 9.633 



10. — .133 = 9.867 



10. + .133 = 10-133 



10, -f .367 = 10.367 



10. + .500 = 10.500 



The apparent inequality of its periods is thus accounted for, which is the minor 

 phenomenon alluded to as one never explained.* 



* A few words upon the bearing which these views have upon some stars presenting kindred phenomena to 

 that of 1572. 



To apply the ring hypothesis to the star seen by Jansen in the Swan in 1600, and by Dominique Oassini in 

 16-55, and subsequently by Hevelius in 1665, we must suppose that its nebulous ring contains several openings, 

 which were successively in a line between the star and the earth at those epochs ; or rather that its one grand 

 hiatus is occupied by detached masses of nebulous matter, which revolve in the plane of the ring. 



The doctrine of revolution about a distant centre explains with singular felicity the variations of period and 

 intensity of the star Omicron in the constellation of the Whale, (sometimes called Mira Ceti.) "It appears 

 about twelve times in eleven years, or more exactly in a period of 331 d. 15 h. 7 m. ; remains at its greatest 

 brightness about a fortnight, being then, on some occasions, equal to a star of the second magnitude, decreases 

 during about three months, till it becomes completely invisible to the naked eye, in which state it remains 

 about five months, and continues increasing during the remainder of its period. Such is the general course of 

 its phases. It does not always, however, return to the same degree of brightness, nor increase and diminish 

 by the same gradations, neither are the successive intervals of its maxima equal. From the recent observations 

 and inquiries into its history by M. Argelander, the mean period above assigned would appear to be subject to 

 a cyclical fluctuation embracing eighty-eight such periods, and having the effect of gradually lengthening and 

 shortening alternately those intervals to the extent of twenty-five days, one way and the other. Vide "Her- 

 schel's Outlines," Chapter 16. 



If the cause of these inequalities be owing to the conditions we have proposed, then the twenty-five days 

 alluded to in Sir John Herschel's account, represent the time required by light to pass over the diameter of 

 the star's orbit, which is, therefore, equal to seventy-five times that of the planet Neptune. 



Should observation establish that the star varies in right ascension and declination in a period corresponding 

 to the above cycle, the determination of the amount of the displacement would give us the only datum wanting 

 to enable us to calculate the distance of the star from the earth. This could then be done with much more 

 accuracy than can be accomplished with its yearly parallax as a basis. 



Who will gild his name by this achievement? 



81 



