206 Mr. 0. Heaviside on Electromagnetic Waves, and the 



evidence that the iron did any good except by lowering the 

 resistance. But about the advantage of increasing the in- 

 ductance of the dielectric there can, I think, be no question. 

 It imparts momentum to the waves and carries them on. 



In Note B to the first portion of my paper " On Electro- 

 magnetic Waves " (Phil. Mag. Feb. 1888), I gave four sets 

 of numerical results showing the influence of increasing the 

 inductance, selecting a cable of large permittance (constant) 

 in order to render the illustrations more forcible. I take this 

 opportunity of stating that the second set of figures relates to 

 the value L = 2^, not 2, of the inductance per centim. The 

 formula used was equation (82), Part II. of my paper " On 

 the Self-induction of Wires " (Phil. Mag. Sept. 1886, p. 284), 

 which is 



Co=2V (R/ / + S g^ ( e ^ + 6-^-2 cos 2Ql)-h 



where 



P or Q = (iSw)*{(R' 2 + L'V)*+L'n}* ; 



where C is the amplitude of current at z = l due to impressed 

 force V sinn£ at z = 0, with terminal short-circuits. When 

 the circuit is long enough to make e _p/ small, we obtain 

 _ (R /2 + I/V)* P| 

 p ~ 2RZ(Sw)* 6 

 as the expression for the ratio p of the steady current to the 

 amplitude of the sinusoidal current. 



The following table is constructed to show the fluctuating 

 manner of variation of the amplitude with the frequency. 

 Drop the accents, and let H/Ln be small. Then, approxi- 

 mately, i „K1 



where tj=m/Lv, 



under no restriction as regards the length of the circuit. 

 Now give y a succession of values, and calculate p with the 

 cosine taken as —1, 0, and + 1. Call the results the maximum, 

 mean, and minimum values of p. 



y- 



Min. p. 



Mean p. 



Max. p. 



y- 



P- 



y . 



P- 



* 



•505 



1-500 



2063 



6 



1-678 



12 



1681 



i 



•521 



•878 



1-128 



7 



2-365 



14 



39 3 



2 



•587 



•686 



•771 



8 



3-378 1 



16 



932 



2065 



•594 



•685 



•766 



9 



5-000 



18 



225 



3 



•710 



•748 



■784 



10 



7-420 i 



20 



550 



4 

 5 



•907 

 1-210 



•924 

 1-218 



•940 

 1-226 



















