60 



KNOWLEDGE. 



[Maboh 2, 1896. 



moved alternately quicKer and slower than they were 

 licenpt'd to do at Chicaijo. And this not fallaoiously, 

 througli a chance concurrence of deceptive data, but by 

 " a law of order " in a " settled kingdom." 



Dr. See tells us what this law is. The diflicuUies of his 

 predecessors have proved to be his opportunity. They 



arose from the attempts, necessarily futile, to treat a 

 ternary as a binary star. His discovery— for such it may 

 be termed — of an obscure disturbing body in the system 

 of 70 Ophiuchi exemplifies yet once more the value of 

 " residual phenomena" — of vexatious incongruities under- 

 mining accepted ai-rangements, and bringing in their 

 train, for many a long day, nothing but experimental 

 failure and mental discomfort. Only by the severe treat- 

 ment prescribed by modern methods can their true meaning 

 be extracted. They have to pass through an ordeal of 

 strict measurement, from which they emerge, if real, 

 definite and unmistakable, while the collapsible sort 

 vanish and are heard of no more. Instances of each kind 

 of result might be cited, but we are here concerned with 

 one that is solid and satisfactory. 



There can no longer be any reasonable doubt that 

 70 Ophiuchi is a triple star, composed of two veritable 

 suns, linked with a body highly influential upon movement, 

 though devoid of appreciable luminous power. Coupled 

 with the shining satellite, it describes round the chief star 

 an orbit of more than planetary eccentricity in a period of 

 eighty-eight years, while revolving in thirty-six round its 

 immediate companion. Now the parallax of this object, 

 reliably determined by Dr. Kriiger, at Bonn, in 1858-1862, 

 amounts to about one-sixth of a second of arc, correspond- 

 ing to a light journey of twenty years.* Hence the mass 

 and dimensions of the system are at once known. Taken 

 together, the three bodies of which it consists possess 

 2-8 times the gravitative force of the sun ; and the mean 

 radius of the path pursued by the subordinate pair is 

 twenty-eight times the distance of the earth from the sun, 

 that of the orbit of Neptune being thirty times the same 

 unit. The stars are, however, at present, separated by only 

 one-third the gap of space which will yawn between them 



* Tlipre Beem? no good reason for siipersetliug as yet Kriifer's 

 parjUax of 0'"1'J2. Sfliur's few recent, measures were'made under 

 such unfavourable conditions as to deeerre, in his own opinion, little 

 confidence. — Jstr. Nach., No. 3231. 



in the year IIJIO. Fur they are just now very near — almost 

 at — periastron, and tliat point of closest approach, trans- 

 planted to the 3 liar system, would be situated about midway 

 between the orbits of Saturn and Uranus, while the apas- 

 tron passage will take place no less than eleven hundred 

 millions of miles beyond the region of Neptune's tardy 

 circulation. 



Turning to the secondary system of 70 Ophiuchi, we find 

 the bright component revolving round its centre of gravity 

 at a distance nearly twice that of the earth from the sun, 

 its round of travel being thus considcriilily wider than the 

 orbit of Mars. The apparent radius of its path is about 

 one-third of a second, and, if the dark body to which it 

 is attached be of equal mass, the interval dividing them is 

 twice as great, so that Dr. See does not despair of its 

 telescopic discovery. For it may not be wholly destitute 

 of stellar lustre ; and if clothed with even the imperfect 

 luminosity of the companion of Sirius, it might, although 

 much smaller, and more than twice as remote, be neverthe- 

 less detected with the Yerkes refractor. A single measure 

 of its place would suffice to determine its mass, which must 

 otherwise remain unknown. 



The distribution of matter in stellar systems is a point 

 of great interest, and of equal difficulty. Relative bright- 

 ness is no guide to it. Satellite-stars are often attractive 

 out of all proportion to their magnitude. Sirius emits 

 ten thousand times more light than its attendant, yet it is 

 only twice as massive. The stars of a Centauri bear equal 

 sway in the system formed by them, notwithstanding the 

 fivefold superiority in brilliancy of one over the other ; 

 and a corresponding disparity seems to exist in the 

 beautiful tinted couple t; Cissiopei.e. Here the yellow 

 primary surpasses its rosy attendant twenty-eight times in 

 light, though no more than three times in mass, according 

 to M. Otto Struve's location of their centre of gravity. 

 Prof. Jacoby, however, proposes to test the accuracy of his 

 result by measurements from the Rutherfurd photographic 

 plates ; and intrepid computers will no doubt come forward 

 to execute his plan, which demands the solution of seven 

 hundred and two equations involving sixty-six unknown 

 quantities. 



Endless gradations of radiative power seem to be repre- 

 sented in the stellar world ; but the discovery of " dark 

 stars," solely through their gravitational effects, must be 

 regarded as a signal triumph of exact astronomy. They 

 are found under varied circumstances. Witness the com- 

 panion of Procyon, unseen, not assuredly through proximity 

 to that lustrous orb, but through real obscurity; the fourth 

 component of ? Canori, and the almost incredibly close 

 satellites of Algol and other eclipse-stars, as well as of 

 i Cephei, and sundry short-period variables ; besides an 

 unknown multitude of undiscoverable orbs, which have 

 ceased or never began to shine, or even of whole systems 

 wrapt in thick darkness. 



Dr. See reminds us that, for the carrying out of the 

 geometrical plan of movement in 70 Ophiuchi, it is a 

 matter of indifference whether the obscure component be 

 attached to the larger or to the smaller star. " While we 

 have spoken," he remarks, " of the dark body as attending 

 the companion, it is clear that similar phenomena would 

 result from the action of a body revolving round the 

 central star. In this case, however, the considerable 

 distance which would result from a period of thirty-six 

 years might render the stability of the system somewhat 

 precarious." 



Perhaps more than precarious. The alternative arrange- 

 ment could apparently subsist throughout a single revolu- 

 tion only by a happy chance. For if we ascribe to the 

 central star and its big planet a combined mass twice 



