THE ELECTRIC IVAVE-EILTER 3 



plied with its assigned narrower range of frequencies. Thus, for 

 instance, with three wa\e-tilters the band of frequencies necessary 

 for ordinary telephony might ^be transmitted to one receiving device, 

 all lower frequencies transmit^jted to a second device, and all higher 

 frequencies transmitted to a" third de\'ice — separation being made 

 without serious loss of energy in any one of the three bands. 



By means of wave-filters ii^terference between difYerent circuits or 

 channels of communication irv telephony and telegraphy, both wire and 

 radio, can be reduced provided they operate at difTerent frequencies. 

 The method is furthermore applicable, at least theoretically, to the 

 reduction of interference between powder and communication circuits. 

 The same is true of the simultaneous use of the ether, the earth return, 

 and of expensive pieces of apparatus employed for several power or 

 communication purposes. In all cases the principle involved is the 

 same as that of confining the transmission in each circuit or channel 

 to those frequencies which serve a useful purpose therein and exclud- 

 ing or suppressing the transmission of all other frequencies. In the 

 future, as the utility of electrical applications becomes more widely 

 and completely appreciated, there will be an imperative necessity 

 for more and more completely superposing the varied applications of 

 electricity; it will then be necessary, to avoid interference, to make 

 the utmost use of every method of separating frequencies including 

 balancing, tuning, and the use of wave-filters. 



Definition of Artificial Line 



The w^ave-filter problem in this paper is discussed as a phase of 

 the artificial line problem, and it is desirable to start with a some- 

 what generalized definition of the artificial line. The definition 

 will, however, not include all wave-filters or all artificial lines, since 

 a perfectly general definition is not called for here. Even if an ar- 

 tificial line is to be, under certain wave conditions, an imitation of, 

 or a substitute for, an actual line connecting distant points, hardly 

 any limitation is thereby imposed upon the structure of the device; 

 an actual line need not be uniform but may vary abruptly or gradually 

 along its length and may include two, three, four or more transmis- 

 sion conductors of which one may be the earth. Having indicated 

 that w^ave-filters partake of somewhat this same generality of struc- 

 ture, the present paper is restricted to wave-filters coming under 

 the somewhat generalized artificial line specified by the following 

 definition : 



An artificial line is a chain of networks connected together in sequence 

 through two pairs of terminals, the networks being identical hut other- 



