On the Electric Force as traversing Interposed Media, 185 
to be the roots of the equation in that case : then the waves 
. 2 7T 2 7T 2 7T 
of which the lengths arc -j- , y-, will be trans- 
mitted without absorption, and consequently will form a num- 
ber of bright lines in the spectrum, yet probably too few to 
afford, by themselves, any sensible light. Now suppose e 
to decrease gradually, then all the roots Aq , ^ 2 ? •• • will 
vary, but not with equal rapidity. Some of them may be 
changed in magnitude considerably by a very small change 
in e, and, consequently, in the parts of the spectrum to which 
these roots respectively correspond, there will be bright 
bands. Other roots may be only slightly affected by a con- 
siderable change in s ; hence there will be, in the parts of the 
spectrum which correspond to these roots, rapid variations 
in the intensity of the light, producing dark bands or dark 
lines. 
Perhaps the equation (42.) which we are considering, may, 
in certain cases, be much simplified; but I cannot proceed 
with the subject any further in the present paper. 
I am, Gentlemen, yours, &c., 
Littlemoor, Clitheroe, Feb. 6, 1840. JoHN Tovey. 
P.S. In my last paper, vol. xv. p. 451, last line but three, 
for increasing indefinitely read increasing or diminishing in- 
definitely, — p. 452, line for cos mi = V — 1 , sin m i 
read cos m i-\- ~1. sin m i ; — p. 453, line for p, a, read 
PiOiii and line 2Q,for a, read ap, — p. 454, line 21, Jvr {‘23.) 
read (33.) ; lines 22 and 23, for e^^ read e^^ 
XXXIV. — On the Direction and Mode of Propagation of the 
Electric Force traversing Interposed Media, By George 
J. Knox, Esq., A.M., M.E.I.J.* 
V^HATEVER theory be adopted to explain the passage of 
" ' the electric force traversing an intervening fluid or solid 
substance not undergoing electrolyzation, — whether we sup- 
pose it to originate in an inductive influence affecting the cir- 
cumambient aether of each particle of the substance in the line of 
direction of the force, in whose alternate states of induction and 
equilibrium consists the passage of the electric current, (the 
rapidity of such changes constituting its intensity,) while the 
vibratory motion produced in the particles of the aether on 
each successive return to a state of equilibrium causes the 
* From the Transactions of the Royal Irish Academy, vol. xix. 
