114 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1953 



Table II - Moment Ratios, Calls Served at Random 



RM = Mk(i - ccy/k\ 



(2 - a)«(3 - 2a)*(4 - 3a)2 

 /6(a) = 432 + 972a - 2016a2 - 437a' + 1790a^ - 528a'^ - 196a6 + 67a7 + 6a8 

 /7(a) = 10368 + 34560a - 89208a2 - 32772a' + 177926a* - 104287a5 - 29260a« 



+ 43876a7 - 9158a8 - 2039a9 + 588aW + 36a» 



and the second approximation is 



2F2(u) = (1 - vW2) e-"^^-«^^^-"^) 



+ (1 + VW2) e-^''-'''^^^' ^^^^ 



which turns out to be a good fit for a roughly less than 0.7. Curiously 

 the corresponding Mellor approximation has a more complicated ex- 

 pression. 



Following the same procedure for three exponentials, it turns out 

 that the correspondent to the set of equations (26a) is 



0'iR2 — Oi + as = Rz 



aiRz - a2R2 + a^ = R, (30) 



(i\Ra — (hRi 4" dzRi = Ri 



with ai = Xi -\- X2 -\- X3 , a2 = XiX2 + X\Xz + 2:2X3 , az — 0:1X2X3 , that is, 

 the symmetric functions. 



