338 Dr. Ketteler on the Dispersion of Light in Gases. 



Jamin*, whicli produced fine and easily traceable systems of 

 fringes. A Geissler's mercurial air-pump f was used in filling 

 the tubes, and in order to compress or rarefy the gases a second 

 pump, consisting of a metal cylinder in which there moved, with 

 as much friction as possible, a piston capable of being slowly 

 and continuously screwed in or out by a proper contrivance. 

 The changes of pressure were read off by a cathetometer, on a 

 manometer consisting of glass tubes 15 millims. wide. The 

 pressure could be augmented, if required, from its ordinary 

 amount to four atmospheres. The plan of the investigation 

 now was, starting from a first coincidence, with mixed light (for 

 instance, red and yellow), and gradually augmenting the pressure, 

 to find the second, third, &c, noting at the same time the cor- 

 responding readings of the manometer. 



The first experiments, however, which were made with air, 

 greatly simplified the process. Successive series of bands, which 

 coincided most accurately with each other, were found for the 

 three possible combinations of colour, namely — 



Yellow : Red. Green : Yellow. 



8 



7 



1-14286 



^ = 1-10526 



104 8 

 91 ~ 7 



13 



' 13 " " 



73-5 21 3-5 



66-5 r 19 ' 3-5 " " 



200 8 



175 ~~7 



25 



25 - " 



147 21 7 



133_ .." 19 ' 7 *"" " 



304 8 

 266"" 7 



1=1-14286 



!**-**.?* -1-10526 

 285 -19 15 - I10Wb 





Gree 



a : Red. 





24 

 19" 



1-26316 



< 



240 24 



10 





190 "19 



10 ~ " 





336 24 

 266 ~~T9' 



14 



^=1-26316 



14 



* Ann. de Chim. et de Phys. 3 e ser. vol. lii. p. 166. 



t Meyer, BeobacMunyen ilber das geschichtete "ekktrische Licht, Berlin, 



1858. 



