212 SPECIAL RESULTS IN THE URA.NOLOGICAL 



as from 14 to 16. ( 357 ) Of these Herculis, since its first 

 discovery, has already twice completed its circuit of revolu- 

 tion ; and in so doing has presented (in 1802 and 1831) 

 the phenomenon of the apparent occultation of one fixed 

 star by another. We are indebted for the earliest calcula- 

 tions of the orbits of double stars to the industry of Savary 

 (in the case of Ursse majoris), Encke (70 Ophiuchi), and 

 Sir John Herschel ; and they have been since followed by 

 Bessel, Struve, Madler, Hind, Smyth, and Captain Jacob. 

 Savary's and Encke's methods require four complete observa- 

 tions sufficiently distant from each other. .The shortest 

 periods of revolution yet known are of 30, 42, 58, and 77 

 years, intermediate, therefore, between those of the planets 

 Saturn and Uranus; the longest periods yet determined 

 with any degree of certainty exceed 500 years, or are about 

 three times as long as that of Le Terrier's planet Neptune. 

 According to the investigations hitherto made, the excen- 

 tricity of the orbits of double stars appears to be extremely 

 considerable, resembling that of comets ; in the case of <r 

 Coronse it is 0'62, in that of a Centauri 0*95. The least ex- 

 centric internal comet, that of Paye,has an excentricity of 0'55, 

 or less than that of the orbits of the two double stars just 

 named ; excentricities much smaller are presented, according 

 to Madler's and Hind's calculations, by r\ Coronse and Castor, 

 being 0'29 in the former, and 0'22 or 0*24 in the latter. 

 In these double stars, therefore, the suns describe ellipses, 

 which approximate closely to those of two of the smaller 

 planets of our solar system, as the orbit of Pallas has an 

 excentricity of 0'24, and that of Juno 0*25. 



If with Encke we regard the brighter of the two stars in 

 a binary system as being in repose, and accordingly refer to 



