452 



NOTICE OF THE ORBIT OF THE 



Captain W. S. JacoVs Orbit of o} and ^ Centauri. 



We thus have here altogether one of the most, if not the most, interesting and 

 important sidereal system in the heavens ; the only one which can compare -with 

 it is 7 Virginis, and that has been looked upon as being amongst the double stars, 

 what IIalley's comet is amongst comets; but though so Avell and frequently 

 observed of late years, it was not iustrumentally measured so early as a Centauri, 

 and it is a much smaller star, with an orbit of only one-fourth the apparent dimen- 

 sions, and a period of time double the length of its southern rival ; so that, while 

 the actual observation for the purpose of carrying theory with fact would he eight 

 times more difficult in the case of 7 Virginis, and loaded with eight times the pro- 

 bable error of observation, there is the further objection, that on account of the 

 greater length of the period, but a small portion of the orbit could be determined 

 by one observer, or even by one instrument. 



But the crowning importance of the binary system of a Centauri, is the accu- 

 rate determination of its parallax or distance fi-om us, by the late Professor 

 Henderson, as we are thereby enabled to speak, not only of the proportions of 

 the different parts of the orbit, but of their actual size, and the weight of the two 

 bodies. Thus the least distance of these two suns is only half that of the earth 

 from the sun, or a little less than that of Venus, while the greatest distance is a 

 little more than that of Uranus ; and the mass of the two stars comes out three- 

 quarters of that of our sun, then* distance from us being 226,100 times our dis- 

 tance from the sun. 



Well, therefore, may Sir J. Hekschel have said, " that no subject more 

 worthy of diligent and continued inquiry can possibly be urged on the attention 

 of southern astronomers." 



