56 



Mr. G. J. Stoney on the Physical 



[Recess, 



sation in one part of the ring tends to disperse the gas which had accumu- 

 mulated there and so restore the balance, with better effect than the slightly 

 superior attraction of the condensed knot can disturb it. The gases first 

 cast off will soon be replaced on the star by a fresh supply of the same 

 kinds diffusing upwards from below, to be in turn flirted off into the rings, 

 if the star have retained sufficient rotation. It would seem, then, that the 

 rings must of necessity consist of exceedingly light materials. These rings 

 will obviously move nearly in the same plane as the companion, or frag- 

 ments of the companion, as the case may be. 



96. Now, as has been explained above, when the circumstances are such 

 as favour the formation of a double star, the perihelion distance of the re- 

 lative orbit is, after every revolution, on the increase, and the eccentricity 

 on the decrease. If the two stars manage to get clear of one another be- 

 fore the eccentricity is worn out*, the process is complete, and a double 

 star has come into being. But it must often happen, and is especially 

 likely f where the companion is small, or has broken up into a number of 

 fragments, that after the perihelion distance has become very considerable, 

 but before the stars are quite clear of one another, the orbit will have de- 

 graded into a circular one. If this happen to any fragment of which the 

 distance is at the time less than the radius of the distended primary, the 

 two bodies must fall together and become one. But if the perihelion dis- 

 tance had attained a sufficient magnitude to place the fragment in one of 

 the rings surrounding the primary, it will there play a very important part. 

 It will by its attraction collect this ring about itself, and thus become 

 covered with an enormous atmosphere, encircled by which it will continue 

 to spin vigorously in the direction in which it moves in its now nearly cir- 

 cular orbit. If this rotation should be rapid enough, the new planet will 

 itself throw off rings ; and if any of these should afterwards become con- 

 centrated into satellites %, they will, like our moon, keep the same face 



* The following eccentricities of double stars have been determined with more or less 

 probability. 



Star. Eccentricity. Authority. 



61 Cygni nearly circular 



£Cancri 0"23 Madler. 



7) Cor. B 0-29 Madler. 



£ Ursas Majoris O'-ll Madler. 



SHerculis 0-43 Madler. 



p Ophiuchi G"47 Sir J. Herschel. 



I Bootis 0-59 Sir J. Herschel. 



§ Cygni 0-61 Hind. 



o) Leonis 0-64 Yillarceaux. 



Castor 0-76 Sir J. Herschel. 



yVirginis C"S8 Sir J. Herschel. 



t Since tangential resistance, which is what shortens the ellipse, acts with much more 

 effect upon a small body than upon a large one of the same density. 



$ Can chemistry haye intervened on the satellites, and formed heavy products out of 

 materials originally very rare ? or may the density and want of atmosphere of these bodies 



