386- THEORY OF OPTICS
complex quantities written in (9); nevertheless they can t equal to these complex quantities and the physical me; can be determined at the end of the calculation from th< parts. This method of procedure makes the calculation simpler.
Now, from (9),
Hence (i) may be written
1 l\ """"" r 4?r T2 or when
if -\Q.
1^1 T '/'"•I \./|
^l.TZ' ^ '**'^;' *'
it follows that
1 l ^n , z' ^i
The similar expression for ^2<?2 is obtained by replacin subscript i by 2. Hence, from (7),
A comparison of this equation with (17) on page
namely, /„.= —•-—, shows that in place of the die J Jx 47t fit
constant e there appears the complex quantity er which de upon the period T( = r • 2 n); thusmmediately written out if X be assumed to be a periodii function of the time. For gl and £2 are proportional to th< same periodic function of the time plus a certain term whicl represents the natural vibrations of the ions, which, according to (i) and (3), take place when X = o. But in considering stationary conditions this term can be neglected, since, 01 account of the resistance factors r^ and r2 , it disappears in th< course of time because of damping. Hence it is possible to se