May 2, 1 2.] 



KNOWLEDGE 



81 



^PV AN ILLUSTRATED "^^ 



MAGAZINE OF SCIENCE 



SIMPLY WORDED— EXACTLY DESCRIBED 



LOXDOX: MAY •?, 1892. 



CONTENTS. 



On the Origin of Binary Stars. Bv T. .T. J. Sek. B.A.. 



i;.Lt.. B>!r 



The Classification of the Chemical Elements. Bt 



Vaigu-^x (-'oRXisn, B.Sc, F.O.S 



The System of Algol. By Miss A. M. Cleeke 



The Great Earthquake in Japan of 1891. Fy tlip 



Rev. H. N. HuTCHixsoy, B.A , F.G.S 



The Great Sunspot and its Influence. By E. W. 



M.wNDEit, F.R.A.S 



Letter -.—T. AV. Backhox-se 



Ants Companions.— T. By E. A. BriLEB 



Hot Springs. By Prof. J. Logav Lobt.et, F.G.S 



The Face of the Sky for May. By Herbert Sadler, 



F.R.A.S. 



Chess Column. By C. D. Locock, B.A.Oson 



81 



S4 

 86 



88 



8!l 

 i)3 

 il4 

 05 



98 

 98 



ON THE ORIGIN OF BINARY STARS. 



By T. J. J. See, B.A., B.Lt., B.Sc. 



WHEN Sir William Herschel was exploring tbe 

 sidereal heavens, he found a great number 

 of stars with close companions, which he 

 frequently measured with a view of detecting 

 relative annual parallax. Ami although in 

 this object he did not succeed, his measurements after- 

 wards led him to a discovery of much greater importance, 

 when he recognised for the first time that some of the 

 double-stars are physical systems in actual revolution. 

 The classic observations of Sir -John Herschel greatly 

 extended the list of double-stars, and more recent 

 measurements show that some 600 of the 10,000 objects 

 now enumerated in various catalogues are binary systems 

 in visible orbital motion. Some of these systems are so 

 rapid that during the last hundred years several 

 revolutions have been accomplished, but by far the greater 

 number are so slow that centuries must elapse before. their 

 great periods are com])leted. Sir William Herschel also 

 perceived the very intimate connection between stars and 

 nebul.T, and appealing only to the law of continuity was led 

 to suspect that nebuhi? in the course of immense ages 

 develop into stars. Following this line of thought, he 



divided the whole assemblage of objects into celestial 

 species, and a great impetus was afterwards given to his 

 speculations by Laplace's formulation of the Nebular 

 Hypothesis, based upon phenomena observed in the 

 motions of the planetary system. The epoch-making 

 discoveries following Dr. Huggins' application of the 

 Spectroscope to the study of the heavenly bodies, have at 

 length confirmed the conjectures of Herschel and Laplace, 

 by showing that many of the nebuhi? are masses of glowing 

 gas in the process of condensation, and hence it now 

 becomes a matter of great philosophic interest to investi- 

 gate the process by which nebuhr have developed into 

 stellar systems. 



About four years ago the writer proposed to bimself to 

 investigate the origin of Binary Stars, and for this purpose 

 collected a table of the orbits of various systems, from 

 which the remarkable fact was discovered that these orbits 

 are very elongated in comparison with the nearly circular 

 orbits of the planets and satellites. It was at once evident 

 that so remarkable and fundamental a diiierence could not 

 be overlooked in explaining the origin of double-star 

 sN'stems, and the higli eccentricities seemed to point with 

 overwhelming probability to the operation of some powerful 

 physical cause which had not left a corresponding impress 

 upon the orbits of the planetary system. Accordingly it 

 was immediately suspected that the cause which had 

 elongated the binary orbits was the secular reaction 

 arising from the tidal friction in the bodies of the stars ; * 

 and this hypothesis has been confirmed by subsequent 

 mathematical investigation, in which methods were fol- 

 lowed analogous to those employed by Prof. G. H. Darwin 

 in his graphical history of the Lunar-Terrestrial system. 

 As the results of this research seem to throw an entirely 

 new light upon the formation of stellar systems, it may be 

 interesting to show, in an elementary geometrical manner, 

 how the eccentricities have been developed by the secular 

 action of tidal friction, and to point out the probable 

 origin of Binary Stars. 



Self-luminous bodies, such as the Sun and double-stars, 

 are certainly in a fluid state (the term riiiiil being used in 

 the most general sense), and there is reason to believe that 

 the viscosity or " stifltiess " of the fluid is usually small. 

 Therefore the tides raised in such masses by the attraction 

 of foreign bodies will not be confined to the surface (as in 

 case of the fluid oceans surrounding the nearly rigid Earth), 

 but will extend throughout the whole mass; such tides are 

 termed hodihj tides, and it is with them that we are here 

 concerned. Now, imagine a double-star system, whose 

 components we shall call respectively Helios and Sol,t 

 each of which is of the same order of mass, and same 

 general physical condition as the Sun. Suppose both stars 

 to be spheroids endowed with rotations which are rapid 

 compared to their period of revolution about one another, 

 in the same direction, and about axes nearly perpendicular 

 to the plane of orbital motion. 



Let the system be started with the spheroids at a con- 

 siderable distance apart, so that the attraction of either 

 upon the other becomes practically the same as if the 

 masses were collected at the centres of gravity, and suppose 

 the orbit given a small eccentricity. Then, since the fluid 

 is more or less viscous, the tides raised in either mass 



* The m-iter had previously seen no intimation that tidal friction 

 could increase the eccentricity, but soon proved it, for the case in 

 which the tides lag as in Fig. 1, only to discover afterwards that a 

 similar result hail been reached by Prof. George Darwin several years 

 earlier, though it had not been given any particular prominence, and 

 was apparently but little known. 



t These names are chosen to fix the attention upon a system com- 

 posed of two sun-like bodies, such as we find in double-star systems. 



