4.84 BARON VON WREDE ON THE ABSORPTION OF LIGHT 
A (cosi+ / — 1.sin 2) 
fie 2 b 
Tog (cosa = + / =i sinan > ) 
bf 46 TAN PSE A 2) 
9 2 ee a b 
1—#* (cos 2x 2° 4 V=T.sinax <) 
If in this expression, in which r is naturally less than 1, we suppose 7 
to be infinitely great, we shall have 
A (cos 2 + /—1.sini) 
(br)? g(t Lat i OY 7 eee eee 
( ) 9 26 ey 2b 4 
1—79( cos 2 x —+WV —1.sn22 
r X 
By separating in this expression the real from the imaginary magni- 
tudes we obtain 
ay =—_ ee ae) 
cos2 (1-9 008 2% —) + r?sin 7 sin2 + Bt: 
=(1 — ra 
and 
sin z (1-7. cos 2x a) +r cosi. sin dx 2° =0. 
From the last expression we obtain 
2b 
r? sin 2 7 — 
r 
J 1-27? cos 27 eu + r4 
26 
— r2 D 7p 
1— r?cos2 7 x 
sin t = 
and 
cost = 
1 = 272 cos 94 22 +8 
If we substitute this value of sini and cos? in the formula (5) we have 
after reduction 
(l—r)?a 
= SS ae (G),.26 2* 
* Considering the partial reflection of a surface as a total reflection of all the 
light in contact with the particles of the body, it is evident that, the form of the 
particles being neglected, and the reflected part being called as before r a, i. e. 
(1 —r) a, that part continuing in the original direction, the whole quantity r a © 
cannot return in a contrary direction, but that a part of the same must be re- 
flected in different directions. To be convinced that such a change in the pre- 
supposed hypothesis does not materially alter the results deduced from it, we 
have only to suppose that the part of 7 @ which is reflected in a contrary direction 
is called r'a, as it is then evident that the intensities of the system of waves of 
