212 BELL SYSTEM TECHNICAL JOURNAL 



were obtained when the sags in the wires were small. Threshold 

 velocity data for the cases of larger sags were obtained by repeating 

 the test in some instances with the wires so tensioned that in cold 

 weather the sags were equivalent to those ordinarily prevailing in 

 warm weather. 



In considering the threshold velocities given in this article and in 

 Table I the relative frequency of occurrence of these velocities has an 

 important bearing upon the amount of contacting to be expected. 

 In Fig. 9 the curve for maximum (comparable to threshold) wind 

 velocities experienced at Chester, shows that for velocities greater 

 than about 20 miles per hour the frequency of occurrence decreases 

 as the velocity is increased. For example, in terms of five-minute 

 periods, winds in a velocity cell of 36 to 40 miles per hour and those 

 of higher velocity have been found to occur approximately twice as 

 frequently as winds in a cell of 41 to 45 miles per hour and higher. 

 Thus, in the vicinity of Chester, a wire arrangement with a threshold 

 velocity of say 40 miles per hour would be expected to be subjected 

 to winds that would cause contacts during approximately twice as 

 many five-minute intervals in a year as an arrangement with a thresh- 

 old velocity of 45 miles per hour. At higher wind velocities an 

 increase of five miles per hour in the threshold velocity will be attended 

 by a greater per cent reduction in the number of five-minute intervals 

 during which winds of sufficient velocity to cause contacts will occur. 



Since these results were obtained from tests using short lines which 

 were relatively rigid as compared to long lines it was thought that this 

 feature should be given consideration by supplementing these tests 

 with a few representative tests on a longer line. Accordingly, ad- 

 vantage was taken of a toll line, in the Pocono Mountains of eastern 

 Pennsylvania, which was to be dismantled and an 18-mile section of 

 the line was equipped with four pairs of wires each with a different 

 spacing. The pairs were connected to a recorder which registered a 

 contact of practically the same definition as the recorder at Chester. 

 Data from this line were recorded for approximately two winter 

 seasons. The results were in substantial agreement with those 

 obtained from the tests at Chester. 



Equilibrium Position of a Span of Wire in Natural Winds 

 With regard to the theory ^ relative to the equilibrium position of 

 a span of wire under the influence of a steady wind, a study was 

 conducted at the Chester site to investigate the applicability of this 

 theory under the varying conditions of natural winds. Owing to the 



1 Loc. cit. 



