Ofi the Electric Force as traversing Interposed Media. 185 

 to be the roots of the equation in that case : then the waves 



of which the lengths are -t— , -7 — , -y- , ... will be trans- 



k^ k\ A-g 



mitted witliout 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 A'l , kc^^ kg. ... will 

 vary, but not with equal rapidity. Some of them may be 

 changed in magnitude considerably by a very small change 

 in s, 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, Sec, 

 Littlemoor, Clitheroe, Feb. 6, 1840. JoHN ToVEY. 



P.S. In ray last paper, vol. xv. p. 451, last line but three, 

 Jbr increasing indefinitely read increasing or diminishing in- 

 definitely, — p. 432, line 14, Jbr cos mi = V' — l . sin wi i 



read cos m i-i- \/ —1. sin mi ;—p. 453, line 28, Jbr p, «, read 

 p^«y; and line 29,Jor a, read a^; — p. 454, line '21, Jar (23.) 

 read (33.) ; lines 22 and 1% for e^^' read e^*' 



XXXIV. — Qn the Direction and Mode of Propagation of the 

 Electric Force traversing Interposed Media. By George 

 J. Knox, Esq., A.M., M.R.I.A.* 



"Vl^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. 



