1921.] Caldwell and Marsden.—Inductive Interference. 
289 
Examining this for the above case we have 
M c -f C/ = *0531 cm. per centimetre, 
or for one mile 
•0531 x 5280 x 30*48 
9 XlO 5 
•00955 mf. 
The addition of a capacity of \ microfarad per mile, an amount not too 
great to affect speech very seriously, would decrease the voltage from 847 to 
—= 15 volts, which would probablv be considered quite safe. 
5-00955 
Such effects have actually been observed, and the method might prove 
useful for portable telephones for linemen. 
Measurements were also made with both transmission-lines alive, and 
the following results obtained :— 
Table II. 
All Wires isolated. 
Others earthed. 
Wires. 
Observed 
Calculated 
Observed 
Voltage. 
Voltage. 
Phase Angle. 
Voltage. 
D-earth 
670 
424 
/225° 42' 
450 
E-earth 
565 
176 
/218° 6' 
190 
F-earth 
555 
181 
/21° 19' 
170 
G-earth 
650 
421 
/14° 4' 
420 
H—earth 
730 
302 
/205° 14' 
430 
K-earih 
715 
303 
/34° 27' 
420 
D-E 
250 
• 
250 
/231° 3' 
D-F 
600 
594 
. /218° 27' 
D-G 
840 
813 
/209° 57' 
D-H 
165 
176 
• ;/262° 27' 
D-K 
735 
724 
/221° 0' 
• • 
E-F 
355 
354 
; /209° 36' 
E-G 
585 
586 
/201° 7' 
E-H 
185 
136 
/8° 24° 
E-K 
500 
480 
/215° 51' 
F-G 
220 
242 
/188° 38' 
F-H 
505 
483 
/23° 46' 
F-K 
155 
133 
/232° 26' 
G-H 
725 
719 
/I8° 44' 
G-K 
165 
.. 
172 
/203° 45' 
H-K 
1 
605 
s; i •') i •- *i * Jf) Pi •/, 
603 
9 rom ■ > 
Nt , .,.. ■ r,, . 
/209° 51' 1 
Comparing these results with Table I, it will be seen that the induced 
voltages are about two-thirds of those with only one line alive. This at 
first sight seems surprising, as one might expect double the effect. The 
reason for the difference is that the induced voltages due to ABC and 
A'B'C' are nearly opposite in phase. In fact, if the line in question 
were situated exactly centrally between ABC and A'B'C' and at the 
same height above the ground the induced voltage should be practically 
zero. 
