Lines in Telephonic Transmission. 



327 



explained, consisted of 300 lengths connected in series. 

 Between each length and the succeeding length a T-14 coil 

 was inserted, the primary in one wire of the pair and the 

 secondary in the other wire of the pair, the connexions being 



Fig. 2. 



e"d 



ia. 



so made as to put the coil into the cable inductively. Each 

 coil added about *11 henry and 12 ohms to the circuit. To 

 ensure the reliability of the test it was necessary to so place 

 the loading coils that the mutual induction should be negli- 

 gible. Accordingly they were spread over all the space 

 available, and tests snowed that any effect of mutual induction 

 between coils was quite negligible. 



The experimental line is shown in the photograph on 

 Plate VI. The three reels of cable are all visible : one is in 

 plain sight, another is at the extreme left, and the third can be 

 distinguished at some distance to the right, The reel at the 

 extreme right had no connexion with this experiment. The 

 cables were brought out to pot-heads, and each wire termi- 

 nated in a screw- cup. In this way any combination of con- 

 nexions could be made. Two of the pot-heads of the middle 

 reel of cable are in plain sight in the phot »graph. The coils 

 were placed upon shelves — being, placed horizontally and on 

 edge on alternate shelves. With this arrangement there was 

 practically no mutual induction except between one coil and 

 the adjacent coil, or two on either side. The four coil ter- 

 minals were carried underneath the shelf to a distributing 

 board between the pot-heads, and this enabled us r > connect 

 in the coils in any desired manner. 



An artificial section was also made and loaded with LOO 

 T-14 coils, and this is seen in the right-hand half of the 

 photograph. The coils upon the shelves are plainly visible. 



Z 2 



