Pocketbook of Useful Formulæ and Memoranda
for Civil and Mechanical Engineers

339 OF ENGINEERING FORMULÆ. Electrical Formulae, by Paget Higgs, LL.D., C.E., and E. 8. Brough—continued, sistance = a°; with leading wires only in circuit = b°; with earth to be tested and first auxiliary earth = c°; with earth to be tested and second auxiliary earth = d°; and with two auxiliary earths = e°. (The mean of the readings with positive and negative test currents to be taken.) 27. The best resistance for a receiving instru- ment on an overland line is (Schwendler) where L = 'rue conductor resistance of line. The best resistance for a cable receiving instru- ment is r = for relays of medium sensitiveness. 28. Let the small letters be expressed in elec- trostatic units, and the large letters in electro magnetic units, then is —n Dimensions of q : m? V1 t I 1 __ 13 —2) C • t I ° _ v . „ c : 3 t~‘j Ö ’ „ r:Tlt ( r _ 1 „ R.-ZiT1 )R~«2’ z 2