Pocketbook of Useful Formulæ and Memoranda
for Civil and Mechanical Engineers

329 OF ENGINEERING FORMULÆ. Electrical Formula, by Paget Higgs, LL.D., C.E., and R. S. Brough—continued. If discharge reading (<7) is in same direction as permanent deflection p, true discharge — Jd* — %dp if opposite — ii. Contacts. (a) When a third wire is Hot available (Schwendler): (Distant ends looped = w'; dis- tant ends insulated = w".) w — VL' + L" — w' (w" — w') X = - ;----—r.---------, m + m where L' and L" are the absolute, and m' and m" the per mile resistances of the two wires in contact. w When w' = w" = w, x = —-------. • . m + m w When m! = m" = m, x — -— . 2 m (&) When a third wire is available (Higgins) : Put one of the wires in contact to earth, and localize the “contact ” as an “earth ” by the loop test. See 7 i (6). iii. Disconnections. (a) By the insulation method: