THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SERIES.] 



JUNE 1894. 



LII. On Interference Phenomena, 

 By Arthur Schuster, F.R.S.* 



1. t^\ OUY f and Rayletgh J have recently ] discussed 

 V_J the question of interference phenomena observed 

 with a source of white light, and have arrived at important 

 results. When the two interfering beams pass through the 

 slit of a spectroscope, the spectrum is seen to be crossed 

 alternately by bright and dark bands, and if high resolving 

 powers are used, these interference effects may be observed, 

 although the difference of path of the two original beams is 

 considerable. This well-known fact has always been taken to 

 prove that the vibrations of the white light are to a certain 

 extent " regular," and efforts have been made to find by 

 experiment the limits of that regularity. The futility of 

 these efforts has been completely demonstrated by Grouy and 

 Rayleigh, who have proved that the bright and dark bands 

 alluded to would appear with sufficient resolving power, 

 even if light consisted of perfectly irregularly distributed 

 instantaneous impulses. These investigations would seem, 

 therefore, to lead to the conclusion that a source of light 

 is completely defined by the distribution of energy in the 



* Communicated by the Author, 

 t Gouy, Journal de Physique, (2) v. 1886. 



X Rayleigh, Encyclopedia Britannica, "Wave-theory," §7: Phil. 

 Mag. xxvii. p. 463 (1889). 



Phil. Mag. S. 5. Vol. 37. No. 229. June 1894. 2 N 



