342 BELL SYSTEM TECHXICAL JOIKXAL 



cusses the (.'fleets of uiihalaiiccs ol ukphone eirciiits (in noise and 

 crosstalk, and describes nietiiods for (ieleeting the presence of these 

 unbalances and locating them when detected. The maintenance 

 of telephone circuits in a high state of efticiency with respect to 

 balance is important since iinlialances contribute to crosstalk between 

 telephone circuits and to noise when such circuits are inNohed in 

 inductive exposures. Difterent types of unbalances are included 

 and their effects under different conditions of energization of the 

 uni)aianced circuit and neighboring conductors are discussed. Methods 

 are described for determining: 



(1) The general condition of c~ircuil> witli reN|)cTl lo balancr liy 

 crosstalk measurements from tluir t(iniiiia!>. 



(2) The approximate location ol unlialaiue> aloiii; a iiiU' !)>• iiicas- 

 iireincnls o\'er a rangi' of freciui'urio willi .i liri(li;t- ai one end ol ihe 

 line. 



(3) The final location of unbal.inci^ li\ liclil inc.i>nrenuiiis wiiji 

 an unbalance deieclor whicii nKi> hi' opcraiiil li\ .i lini-nian .iiul 

 w iiirh usual I\" does nol re(|uire intiTrnpl ion ol Icicplione service, I'xci-pt 

 inonu'nlarily. 



Toil circuit oltice unbalances are brielK' discussed and a sjieci.d 

 bridge for detecting and measuring ihe tnibalances ol composite sets 

 is described. A mathematical treatment ol the bridge method for 

 locating unbalances and a discussion of the tiecessity of terminating 

 the circuits invoked in the tests in their characteristic line impetl- 

 anies are given in an appeiidi.x. The luethods and apparatus 

 described are wideK- tised in the Bell System and afford operating 

 telephone companies means for maintaining their circuits in the 

 condition of minimum practicable unbalance. 



The Theory of Prohabilily and Some Applications lo F.ni;_iiiceriiii^ 

 Problems.'' K. C". IMoi.iN.v. The |)urpose of this pajjcr is to sug- 

 gest a wider recognition b\- engineers of a body of principles which, 

 in lis mathematical form, is a powerful instrument for the solution 

 of practical problems. Certain fimdaiuental |irinciples of the theory 

 of probabilities are stated and ajiplied to three j)rol)lems from the 

 field of telephone engineering. 



Note on the Least Mechanical Ei/nivalent of Lii^lit.'^ Hi;Kiu:Kr K. 

 Iviis. In this paper the \alue for ilie brightness of tin- bl.ick body 

 at the melting point of platinum reientK- obtained b\ ilu writer is 



' Journal A. I. M. K., Vol. 44, p. 122, 1925. 



'Journal of the Optical .Society of .-Xnifrican and Rev. of .Scicnlilic Inslruineiits, 

 Vol. Id, .N". .?, M.ircli, 1<)2.S, p. 289. 



