[ 563 ] 



XI. 



ON THE CAUSE OF DOUBLE LINES AND OF EQUIDISTANT SATELLITES 

 IN THE SPECTRA OF OASES. By GEORGE JOHNSTONE STONEY, 

 M.A., D.Sc, F.R.S., Yice-Presldent, Royal Dublin Society. 



[Bead Maech 26 and Mat 22, 1891.] 



CONTENTS. 



CHAP. PAGE 



I. — Introduction, . .'■ 563 



II. — The problem treated dynamically, . . . . . . . .569 



III. — The problem treated from tte standpoint of the Electro-magnetic Theory of Light, . 582 



IV. — Analysis by Fourier's Theorem, .......... 585 



v.— Illustrations, 592 



VI. — Applications, 594 



Postscript, 607 



CHAPTER I. 



INTRODUCTION. 



The study of the kinetic theory of gases has been pursued during the last forty 

 years with great success, by Clausius, Clerk Maxwell, and others, and has thrown 

 a flood of light upon the conditions under which the molecules of ponderable 

 matter subsist in the world about us. By these investigations it was discovered 

 that, while in solids and liquids they are so crowded together as to be unremittingly 

 under the influence of one another, a very different state of things prevails in 

 gases. In gases the moments of time during which the molecules are close enough 

 to act on one another are brief compared with much longer intervals which elapse 

 between their encounters. During these comparatively long periods of indepen- 

 dence each molecule is free to move in its own natural way ; and important physical 

 events on a large scale take place as a consequence of the motions within the 

 molecules which then occur. 



Previously to these inquiries, Dulong and Petit had obtained by experiment the 

 law that the specific heat at constant volume of the more perfect gases is inversely 

 proportional to their specific gravity. It is further known by experiment that y, 



TEANS. EOT. DUB. SOC, N.S. VOL. IV., PART XI. 4 L 



