THE NATURAL PERIOD OF LINEAR CONDUCTORS 



417 



High Frequency Wave Meter 

 A pair of Lecher wires constitutes a wave measuring system much 

 too awkward and extended for rapid use, and some apparatus much 

 more portable and speedy in operation is necessary; especially when 

 running resonance curves. Such an apparatus is a pair of heavy 

 uniform and parallel conductors arranged with one or two sliding 



metallic short-circuiting discs so as to constitute a quarter or a half 

 wave length "Lecher frame" (see Fig. 5). Such a frame, if containing 

 sufficient copper, is very sharply resonant, need only be a quarter 

 wave length long, and after calibration becomes a wave length meter 

 indicating to a precision of 1 part in 2,500 with the greatest ease. 

 As an accessory apparatus such a wave frame was constructed, 

 calibrated, tested for factors affecting its accuracy and used for most 

 of the measurements reported above. 



The Lecher frame shown in Fig. 5 was made of a pair of straight 

 copper tubes L27 cms. diameter spaced 10.1 cms. center to center 

 and sliding through a brass disc 15.5 cms. diameter, 0.3 cm. thick, 

 with inserted guide tubes. It had a workable wave length range of 

 4 to 7.5 meters and the resonance setting was indicated by a three 

 turn coil-thermocouple-microammeter combination placed with coil 

 clearing one of the rods at the disc end by approximately two cms. 

 It was ordinarily cleaned to make good contact at the disc guides but 

 at no time was any indication noticed of an apparent lengthening of 

 the frame due to a moving back inside of the guides of the contact 

 point. It was calibrated over its whole range in terms of the Lecher 



