1921.] Caldwell and Marsden.—Inductive Interference. 
28T 
The lines experimented upon are shown in fig. 2. 
ABC and AjBjCj. are the main transmission-lines, sometimes energized 
singly and sometimes in parallel. In the latter case A A x , B B 1? &c., are 
corresponding phases. HDE and KFG are sections of 11,000-volt three- 
phase feeders about a mile long, temporarily isolated for the sake of the 
experiments. LM and NO are the transmission-line telephone circuits. 
Voltages were measured by electrostatic voltmeters. 
Data assumed: Transmission-line conductor, 7/T35" aluminium, •405" diameter ; 
11,000-volt feeder conductor, 7/14 S.W.G. aluminium, ’24" diameter; telephone-line 
conductor. No. 8 S.W.G. iron, T6" diameter. 
It may be useful to describe here a voltmeter used throughout these- 
experiments because of its portability, ease of construction, small capacity, 
and almost perfect dead-beatness. The voltmeter is a simple gold-leaf 
electroscope as shown in fig. 3. The case is of thin sheet metal, the glass 
front and back being made airtight. The scale, which is easily read 
to 10 volts, is shown three-quarters size, and the calibration is effected 
by means of an ordinary Weston standard voltmeter and potential 
transformer. 
