(51) 
Expressed physically, the relation between the amplitudes of the 
electric and the magnetic vibrations is such that at any moment 
U, = Um. Expressed geometrically this is: If the extremity of D 
lies on the electric ellipsoid, the extremity of ® lies on the magnetic 
ellipsoid. We may add that the extremities of € and 5 will lie on 
the two reciprocal ellipsoids. 
So we have found: 
ue s ge—hb (39) 
ee An hak 7 
s ha—fe 
= — : aye . (40 
v AnU’ st 
ae 
edt ie 
» .4nU 
which we may also write: 
Mths esr, (BD). tbe eee 
Se = it array | 
From this we derive: 
An U 
) 
BD sin (BD) 
and so according to (38): 
5 » DE cos (D €). BH cos (B D) v2  €cos(DE) H cos (B H) 
oo 0" — A —_ == — $$ ——— 
B D? sin? (BD) sin? (B D) D B 
and by (5) and (17): 
v 
i 
fs. tk (PORN, en nen (43) 
a 
According to this equation the normal velocity s is equal to », 
divided by the area of the parallelogram on the radii veetores of 
the electric and magnetic ellipsoids, resp. in the direction of the 
electric and magnetic induction. 
If the directions in the wave-front, along which the electric and 
magnetic induction can fall are I and IL, then we get: 
