TELEPHONE LINE WIRE SPACING PROBLEMS 201 



However, the recording apparatus was designed to record a contact 

 that would affect telegraph transmission, which mode of communica- 

 tion was considered to be more sensitive to this type of interference 

 than any other form of transmitted signal. This contact was defined 

 as having a minimum duration of 0.01 second and a resistance of 

 20,000 ohms or less. The voltage applied to the lines during the test 

 was 260. This voltage was the highest that would obtain on an 

 open wire d-c telegraph line and would occur when one side of the 

 circuit had a potential of minus 130 volts and the other side plus 

 130 volts. 



Considerable study was given to the selection of apparatus for 

 recording wind velocities. After studying the various types of 

 available instruments and consulting with the United States Weather 

 Bureau, a Burton type of anemometer associated with an Esterline- 

 Angus graphic recorder was selected as best meeting our requirements. 

 This anemometer assembly comprised a four-cup anemometer with 

 the armature of a magneto mounted on the cup-shaft. The magneto 

 current which varies with the rotational speed of the cups was recorded 

 on a milliammeter specially designed for the purpose. This recording 

 milliammeter had several chart speeds so that considerable detail in 

 the velocity change could be obtained when required. The instrument 

 was calibrated to read directly the instantaneous velocity of the wind. 

 A wind vane which registered sixteen directions of wind provided a 

 continuous record of wind direction on the same chart with the wind 

 velocity. The mounted anemometer and the wind vane are shown in 

 Figs. 4 and 5, respectively. 



It was realized in selecting such a velocity recorder that our records 

 would not be directly comparable to the weather bureau records which 

 are five-minute average velocities rather than instantaneous velocities 

 unless relations between the two could be established. For this 

 reason when analyzing the wind velocity charts two velocities were 

 read, namely the average and the maximum for each five-minute 

 interval. To further the comparison it was established that the 

 maximum instantaneous velocity ranged greater than the five-minute 

 average velocity by an average figure of 1.4 for velocities greater than 

 15 miles per hour. This figure which applies to the Chester location 

 and the Burton instrument was obtained by taking the average ratio 

 of the maximum velocities to the five-minute average velocities for 

 500 cases. Figure 6 shows the frequency distribution of these 500 

 cases. This graph indicates that the modal value of the ratio as well 

 as the arithmetic mean is approximately equal to 1.40. Two-thirds 

 of these cases fall between ratio values of 1.25 and 1.55. 



