(62) 
1 
a (CBs Hee Con CE nm 
1 1 4 1 
“f(g ain) tga) 
( Ld nm Ja he a Ne om ar Ee Nm Re 
+ o( Sg (eon . (54) 
hd Ze Ce, 8m \ we vt 
(A? & n+ B? Cem + Ge Hem) (Ate B? en ek Cl He) = 
As was to be expected this equation is symmetrical in the 
electric and the magnetic quantities, though the deduction was 
asymmetrical. 
9. It is now possible to deduce the equation in the coordinates 
_of a point from this equation in tangential coordinates, but in order 
to find at the same time some properties of the radius vector of the 
wave-surface, — which we shall call ray of light, I take the following 
course. We first determine the transformed wave-surface. Let 
4, « and v be the direction cosines of the ray of light and @ 
the radius vector of the wave-surface, which we call the velocity 
of the rays; we take the same symbols for the transformed surface, 
but distinguished by accents. 
Q' 
i darter op) = 
Vuur My Me 
, then: 
s! sl 
IN an! eon Sen en ha eee 
Al 
If now U, m', n' and s’ are made to change a little, so that 
equations (53) and U? 4m? +n? = l continue to be satisfied, then 
NW, gl, v' and eg", do not change, being the coordinates of a point 
of the envelope, so that: 
ds" 
M dt + dm + vd! — 7 = 0, 
" 
U dl +- m' dm! +-n'dn' = 0, 
U dl m' dm! n' dn 
ax v?—s' ay vas"? ap vis? 
2 m'? ni? 
EEN en an Ld 
Lars "(ay ®—s")2 (ats 
