184 



KNOWLEDGE 



[August 1, 1890. 



binary. An orbit computed by the present writer in 1886 

 makes tlie period 18-69 years, but recent measures seem 

 to sbow tliat the true period is somewliat longer 

 — perliaps about twenty years. Fig. 1 repre- 

 sents tlie apparent orbit, and shows the position 

 of tlie companion at difierent times from 1878 

 to 1889. 



3. 42 Coniit Hereniics. — The period of this star 

 has been accurately computed, and is about 25f 

 years. The orbit is remarkable from the fact 

 that its plane passes through, or nearly through, 

 the earth. The orbit is therefore projected into 

 a straight line, as shown in the diagram, 

 Fig. 2. I have also drawn the iral orbit, as 

 it would appear could we view it from a point 

 at right angles to its plane. I find that the 

 plane of the real orbit is at right angles to the 

 general plane of the Milky ^Yay. 



4. j8 Dcljiliini. — The close duplicity of this 

 star was discovered by Burnham in 1873. The 

 period is short, but still somewhat doubtful. 

 Celoria finds lG-95.5 years, Doubiago 26*07, 

 and the present writer 30-91 years. Celoria's 

 orbit is perhaps the best. 



5. i Hcrculis. — Three complete revolutions 

 of this remarkable pair have been performed 

 since its discovery by Sir William Herschel in 

 1782. Se\X'ral orbits have been computed, 

 but Dr. Doberck's, with a period of Sl-411 



6. r] Coronte Borealis. — Some forty years ago it seemed 

 uncertain whether the period of this interesting binary 



,"«T 



Fig. 3. — Apparent Okbit of ^ Herculis. 



star was 43 or 66 years. But now that a com- 

 plete revolution has been described, the question 

 has been decided in favour of the shorter period, 

 ^jj, ,i About a dozen orbits have been computed, and 

 '£1x1-'^^-'^'^ of these those by Dr. Doberck and Dr. Duner, 



T gi^Tng a period of about 41^ years seem to be 



/ the best. The components are of nearly equal 



magnitude (6 and 6^), but at their present distance 



ilSi^lAJi, nil. 



y 



/U.U Orltl I 



/Stalt cj /'■■'Li'iiUs 



Yic. i. — 42 CoM-t; Beeenices. 



years, is perhaps the best. From his elements I have 

 drawn the apparent elhpse represented in Fig. 3. The 

 companion is now near its maximum distance {\\ seconds) 

 from the primary star, and is within the reach of tele- 

 scopes of moderate size. The companion is, however, 

 rather faint, being only 6| magnitude, while the principal 

 star is of the 3rd magnitude. When at their nearest some 

 observers have spoken of "an occultation " of one star by 

 the other ; but the diagram will show clearly that no real 

 occultation ever takes place, the components never ap- 

 proaching within half a second of arc. An occultation of 

 one component of a binary star by the other cannot take 

 place except — as in the case of 42 ComsB — the plane of 

 the orbit passes through the earth. 



Fig. 4- — SiRirs. Apparent Oriht, 



