448 



1 1 dn 



^ = 1- ^-"^7; (3) 



ft {i a/ 



For the wavelength of the sodium lines this becomes: 



0.451. 



We see, therefore, that the. value deduced by formula (3) deviates 

 more from the result of the observations than the value given hy 

 the simple formula (2). 



"SoUte es geliugen, was zwar schwieri^, aber nicht unmöglich scheint, 

 experimenten zwischen den Gleichungen (3) und (2) zu entscheiden, 

 und sollte sich dabei die erstere bewahren, so hatte man gleichsam die 

 DoppLER'sche Verandernng der Schwingungsdauer far eine kiinstlich 

 erzeiigte Geschwindigkeit beobachtet. Es ist ja nur unter Beriick- 

 sichtigung dieser Verandernng, dass wir die Gleichung (3j abgeleitet 

 haben". ') 



It seemed of some importance to repeat with light of dilferent 

 colours FizEAu's experiment, now that the correspondence between 

 theory and observation had become less brilliant, and in view of 

 the fundamental importance of the experiment for the optics of 

 moving bodies. 



From the point of view of the theory of relativity the formula (8) 

 is easily proved, as has been pointed out by Laue "), neglecting 



terms of tlie order — . Recently, however, again some doubt as to 



the exactness of Lokentz's term has been expressed. I may refer- 

 here to a remark by Max B. Weiinstein ') in a recent publication 

 and to a paper by G. Jaumann ^). The last mentioned physicist gives 

 an expression for the coefticient f, which for water does not differ 

 much, but in other cases deviates very considerably from Fresnel's 

 coefficient. 



The interference fringes were produced by the method of Michelson. 

 The method of observation introduced will be described later on. 

 The incident ray sla meets a slightly silvered plate at a. Here it 

 divides into a reflected and a transmitted part. The reflected ray 

 follows the path abc d e a /, the transmitted one the path 

 a e d c h a f. These rays meeting in the focal plane of ƒ have 



1) LORENTZ. Versuch u. s. w., 102. 



2; M. Laue. Die Mitluhrung des Lichtes durch bewegte Körper nach dem Re- 

 lativitatsprinzip. Ann. d. Phys. 23, 989. 1907. 



3) Max B. Weinstein. Die Physik der bewegten Materie und die Relalivitats- 

 theorie. Leipzig. 1913, see note on p. 227 of his publication. 



^) G. Jaumann. Elektromagnetische Theorie. Sitzungsber. d. Kaiserl. Ak. der 

 Wiss. Wien. malliein. nalurw. Kl. 117, 379. 1908, especially p. 459. 



