216 BELL SYSTEM TECHNICAL JOURNAL 



deflection of the suspended wires from a vertical plane in a natural 

 wind could then be computed, equation (4), Appendix I, since the 

 sine of this angle is equal to the horizontal displacement divided by 

 the stretched sag of the wires. If the supports were assumed to be 

 rigid the stretched sag could be calculated directly through the use of 

 equation (3) in Appendix I. However, despite the precautions taken 

 to prevent movements of the pole supports it was found that the poles 

 would bend when the tension in the wires varied. For this reason the 

 deflection of each pole for various wire tensions was measured and this 

 factor was taken into account in determining the stretched sag. The 

 correction applied to the stretched sag as computed from equation (3) 

 was in some cases as great as three inches. Furthermore since the 

 length of wire varies with temperature the particular temperature at 

 which a picture was taken had to be given consideration in computing 

 the stretched sag. 



Following the procedure described above, 20 values of the angle 

 representing the equilibrium position of the wires were obtained for 

 each two-mile-per-hour cell of transverse or normal wind velocity over 

 a range of 17 to 55 miles per hour. The average experimental angle 

 was computed for each velocity cell and the degree of dispersion of 

 the individual values was determined in the regular manner. 



Table II gives the values of the angle of deflection of the wires 

 calculated from the experimental data, also the average angle and the 

 best estimate of the true standard deviation for each two-mile-per- 

 hour wind velocity cell. For comparison the theoretical angle of 

 deflection as computed through the use of equation (1) is given for 

 each cell. The maximum and the minimum angles determined 

 experimentally might be plotted versus the theoretical angles, but 

 these data furnish no definite measure of the dispersion since maximum 

 and minimum values depend upon the number of observations made. 

 For this reason the degree of dispersion was determined for single 

 observations and for averages by obtaining an estimate of the true 

 standard deviation which is independent of the number of observations. 

 Figure 11 shows the frequency distribution of the angles determined 

 experimentally and also the " three-sigma " limits for the wind velocity 

 cell of 25.1 to 27.0 miles per hour. 



In Fig. 12, the average experimental angle for each velocity cell 

 was plotted against the theoretical angle as given by equation (1) and 

 a regression or trend line was determined for these points. For 

 comparison with this line is given a reference line of exact agreement. 

 The "three-sigma" limits for single observations and for averages of 

 20 observations, were also plotted against the theoretical angle in 



I 



