100 On Interference Phenomena in Electric Waves. [June 15, 



completely masks the absorption effects. The intensity of the trans- 

 mitted ray does not steadily decrease ; on the contrary, far more may 

 be transmitted through a thick than through a thin layer of the ab- 

 sorbent medium. The transmission follows the same general law as 

 for light with a thin plate; we are, in fact, dealing with a "thin" 

 plate a plate whose thickness is comparable with the wave-length. 

 The intensity of the transmitted ray is a minimum for a plate J X 

 thick, a maximum for -J X thick, a minimum again for f X, and so on. 

 The points on the curve round the maximum at JX are somewhat 

 irregular, and the two maxima do not absolutely agree. Taking the 

 mean, we may say the wave-lengths in air and water are respec- 

 tively : 



\a = 900. X w = 108 cm. 



This gives us for the coefficient of refraction and the dielectric 

 constant 



n = 8'33. K = 69'5. 



The following are the values of K found by previous investigators, 

 all that are known to me : 



Excluding the Russian physicist as a negligible minority, it will 

 be seen that my value of *; is somewhat low. The cause may lie in 



* ' Wied. Ann.,' vol. 48, p. 35, 1893. 



t ' Phil. Mag.,' vol. 31, p. 200, 1891. 



I Hid., vol. 34, p. 341, 1892. 



' Wied. Ann.,' vol. 33, p. 13, 1888. 



|| Ibid., vol. 36, p. 792, 1889. 

 IT Ibid., vol. 45, p. 370, 1892. 

 ** Ibid., vol. 46, p. 513, 1882. 

 ft ' Phil. Mag.,' vol. 34, p. 388, 1892. 





