416 Etc JJ — Gihbs* Geometrical Presentation of the 



Fig. 4 is drawn for light incident upon a glass (-;? = l-53) — air 

 surface at 48°. The angles of phase difference are : angle 



46°, angle 234 (R 8 ) = 56°. The maximum 



412 



\l 



difference of phase between the two components = ir — 4 



tan 1 -- 1 - = 47°. 

 1-53 



"We have hitherto considered perfectly transparent bodies. 

 We will now consider the general case, so called Metallic 

 Reflection. The general expression for the light disturbance 

 mav be written : 



X= Ae 



IttTcw 

 ~X e 



; (t-!D 



where Xis the instantaneous force, A = amplitude, X = ware 

 length, T = period, t = time, w = coordinate for the direc- 

 tion in which the light waves are advancing, and h — 



Coefficient of Absorption, i. e., the amplitude is reduced to 



If we write the 



— of its initial value in a distance „ , 



e 2ir/C 



above equation in the form : 



2iri / t w 



X = Ae \ X X 



and determine the reciprocal velocity of the light waves, we 



T 



(i -a-)) 



obtain the complex expression 



X 



( 1 — ik) . The real part, 



T 1 



— , is the ordinary reciprocal velocity, — , or proportional to 



