290 BELL SYSTEM TECHNICAL JOURNAL 



orienting the detector to obtain maximum deflection. These data 

 confirmed not only the directions of the lines of force but their relative 

 density as well. 



There is one characteristic of the //o and 7/i configurations that at 

 first sight seems inconsistent with our more usual views of electricity. 

 It is the existence of a substantial tangential component of electric 

 force apparently in close proximity to a metallic conductor. It must 

 be borne in mind however that these frequencies are extremely high 

 and that these distances after all represent an appreciable part of a 

 wave-length. 



If any of the four types of waves depicted above are propagated 

 through a wire of dielectric material without the metal enclosure, 

 lines of electric force which previously attached themselves to the 

 inner walls of the sheath, in general, extend into the surrounding space 

 and close as loops. This means that as the wave moves along the 

 guide a portion of the wave power is propagated through the dielectric 

 itself and a part through the surrounding space. The proportionate 

 parts of the electric and magnetic fields resident inside and outside 

 the dielectric are amenable to calculation. As might be expected they 

 depend both on the dielectric constant of the material and on the 

 proximity to cut-ofT at which the guide is operated. Results of such 

 calculation for the Eo type of wave are shown in Fig. 3, each for various 

 proximities to cut-ofT. A dielectric constant of 81 is assumed. 



For high dielectric constants and for frequencies far above the cut- 

 off, the power is propagated largely inside the guide whereas for low 

 dielectric constant and for frequencies just above the cut-off, a sub- 

 stantial amount of the power travels outside the guide. In the first 

 case inductive disturbances communicated to neighboring guides are 

 very small and correspondingly the guide is substantially immune to 

 outside disturbances. In the second case these important advantages 

 are absent. 



As already stated, many of the properties of wave guides are amen- 

 able to calculation. Formulas for the purpose are included in the 

 mathematical paper already referred to. Certain of these properties 

 are intrinsic — as for example, velocity of propagation, attenuation 

 and characteristic impedance. Others may be regarded as extrinsic 

 in that they result largely from the manner in which the guide is used. 

 Examples of the latter are frequency-selectivity and radiation. 



Velocity of Propagation- 

 It will be remembered that the velocity of electric waves over 

 ordinary conductors immersed in a particular medium is substantially 

 that of light for that medium. In other words it is equal to the velo- 



