4 
Dispersion of Colors in perfectly transparent Media. 271 
ie t Q2 Pe t I U 
so w—*2 +Bi#+C'y eee as i (17) 
our general equation (11) becomes 
Oss ss ae 
¥ pig ?p o) (18) 
where H and H’ will be constant for any given direction of 
oscillation, when A, B, etc., and A’, B’, ete, are constant. I 
we wish to introduce into the equation the absolute index of 
refraction (nr) and the wave-length in vacuo (4) in place of V 
and p, we may divide both sides of the equation by the square 
of the constant (%) representing the velocity of light in vacuo. 
Then, since 
Vee 
Our equation reduces to 
H 22 
nm? 2nke At > (19) 
It is well known that the relation between n and 4 may be 
tolerably well but by no means perfectly represented by an 
equation of this form. 
1 we now give up the presumably inaccurate supposition 
that A, B, etc., and A’, B’, ete., are constant, equation (19) will 
still subsist, but H and H’ will not be constant for a given 
direction of oscillation, but will be functions of p, or, what 
1%; C,—a 
that the values of &, 7, € are changed,) this constraint, accord- 
mg to the principle cited, will not affect the period of oscilla- 
