
between Optical and Electrical Qualities of Metals. 167 
or for the entering intensity 
(100—-R) = = 3) GP <>) 
Herein A means the electric conductivity of the metal in 
absolute electrostatic measure and 7 the period of oscillation 
in seconds. The formule are only valid for sufficiently large 
A, which make the product Ar very large compared with 
unity, a condition always fulfilled with sufficient approxima- 
tion here. When introducing into equation (2) the wave- 
length ) measured in yw, in place of the period of vibration, 
Besides, if we introduce 7, the period of the vibration in seconds 
or 
os 
n 
we have 
y=i(¥ 4A7727+1+1) 
and 
2=1( /4A77?7+1—1). 
These two equations characterize the whole optical behaviour of the 
metal. 
For normal incidence the reflecting-power R, of the metal surface 
bordering on the yacuum is expressed—as is well known—by the 
formula 
ED me daa 
Le (v+-1)*+9° ? 
the intensity of the incident radiation being equal to unity; and, after 
substituting our values of v and g, 

p . MEV FIt1-V 2(V 4 $141) 
© ENP E141 4/20 ie +141) 
For sufficiently long waves, 7. e. for sufficiently large values of r, the 
unit may be neglected as compared with 4A°*r*, and we obtain, in first 
approximation, 



fees es 
= = 
and — PH? 7; 
Finally, if we express the reflecting-power in percent. of the incident 
radiation, as has been done in this paper, we arrive at 
2k 
aa MAS 
which is identical with our equation (2). 
