1893.] Phenomena somewhat analogous to Newton s Rings. 

 The values occur as in the following table : 



93 



(4) We see, on inspection of (18), that the values of It and I, 

 (when plotted as the ordinates, the values of I being the abscissae) 

 form a damped wavy curve, but that neither the damping nor the 

 wave-form are of the simplest type. 



(5) On putting t z = oo, U disappears, and we have 



1 Z> 2 



IT/TO- 1+6 2 



(19). 



(6)* On putting a = 0, that is, removing the primary damping 

 from the expression for the wave, we obtain 



and 



i 



(20), 



the ordinary expressions for the case of the interference of light in 

 thin plates (see, e.g., Preston's ' Theory of Light,' 1890, pp. 145147). 

 21. The theoretical values of I t /I from equation (18) are plotted 

 in curve No. 1, for the following values of the constants, the abscissae 

 representing Z, and the ordinates I^/Io. 



log. dec. 7! = 2?ra//3 = 0'5, 



C 3 L 2 = dLi ; 



therefore X 2 = \ r and v 2 = Vi, 



Xi = 9 m., 



whence b = 0'8, 



by equation (13). 



* For -this suggestion and for much valuable help in checking mathematical 

 working and results I am indebted to Mr. GK Udny Yule. 



