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BELL SYSTEM TECHNICAL JOURNAL 



wire system already mentioned, calibrated not once but various times 

 and unfailingly indicated 3.1 cms. too short. That is, the distance 

 "^" from open end to disc was 3.1 cms. short of X/4, or X = 4((/ + 3.1). 

 It was not found possible to make a trombone slide which maintained 

 its spacing accurately, and before each reading was completed a 

 paper template was laid on the open end and the tubes given a slight 

 bend to obtain parallelism. The setting was then completed. This 

 process was much less bothersome than might appear from its de- 

 scription. 



A 35 X 44 cm. copper plate was clamped to the brass disc to increase 

 its effective area. This brought the 3.1 cm. correction down to 2.67 

 cms. (measured at 5.29 meters wave length). The end effect is there- 

 fore chiefly due to the open end. No doubt it will change if the 

 spacing of the Lecher frame is changed; the fortunate feature is that 

 it appears constant for a given spacing. 



To obtain an idea of the effect of a slight degree of non-parallelism 

 and the presence of insulation material, the rods were first bent out, 

 then in, next a 1.3x3.8x12.7 cm. hard rubber block was laid flat 

 across the outer end and finally this block was laid across the middle 

 of the frame. The results were: 



Obviously a slight divergence is an advantage rather than otherwise, 

 for an uncalibrated frame, and dielectric spacers at high potential 

 points are sources of noticeable error. 



BIBLIOGRAPHY 



Abraham, M. Ann., 2, 32, 1900. Elektrische Schwingungen in t-inem Frei Endingenden Dralit. 

 KiEBlTZ, F. Ann., 5, 872, 1901. Uber die Elektrischen Schwingungen eines Stabformigen Leiters. 

 WiLLARD AND WoODMAN. Physical Rev., 18, 1, 1904. A study of the radiations emitted by a Righi 



vibrator. 

 Rayleigh. Phil. Mag., 8, 105, 1904. On the electrical vibrations associated within terminated 



conducting rods. 

 Pollock. Phil. Mag., 7, 635, 1904. A comparison of the periods of the electrical vibrations associated 



with simple circuits. 

 Cole, A. D. Phys. Rev., 20, 268, 1905. The tuning of Thermoelectric receivers for electric waves. 

 Blake and Fountain. Phys. Rev., 23, 257, 1906. Reflection of electric waves by screens of 



Resonators and by Grids. 



