414 NEUMANN ON ESTIMATING THE INTENSITY OF LIGHT. 
, _ Sin? (sin? 6! — 1) — cos? ¢ sin? ¢! 
~~ sin? $ (sin? ¢! — 1) + cos? ¢ sin? 9! 
B! = _2 Sin $ cos > sin q¢' vsin? g'—1 4, 
sin? $ (sin? ¢! — 1) -+ cos? 9 sin? ! , 
and from 6 and c, 
, _ Sin? $ cos? ¢ — sin? ¢! (sin? ¢'—1) 
~~ gin? $ cos? $ + sin? ¢! (sin? 9! — 1) 
C 
= 2 sin > cos ¢ sin ¢! V sin? g! — 1. 
sin? cos? 9 + sin? 9! (sin? g’/—1) ” 
which are exactly Fresnel’s formule, from which he deduced the 
difference in the retardation of the two component rays polarized 
at right angles to one another on total reflexion, and thus the 
laws of elliptical polarization resulting from this*. 
* Ann. de Chim. et de Phys. t. xlvi. p. 225. 
