Pocketbook of Useful Formulæ and Memoranda
for Civil and Mechanical Engineers

333 OF ENGINEERING FORMULÆ. Electrical Formula;, by Paget Higgs, LL.D., C.E., and R. 8. Brough—continued. and 2-i-? and dx deflection with cable; g being s galv., and s shunt resistance. , ) = cons^ant °f instrument. 13. The retardation characteristic of any cable is (Thomson) where I is its length, k its resistance, and c its capacity per unit of length in electrostatic units. The retardation is a minimum (for a given D) when D = 1 • 649 d. When k is expressed in ohms, c in microfarads, and I in knots (Jenkin), 0-02332 , „ , a = ———— kcl2 seconds; 106 and the speed of signalling with mirror is, in words per minute (Clark and Sabine), 130,000,000 n ~ T7/2 through guttapercha cables; 176,000,000 . h = —----------through Hoopers cables. kcl- The speed of the Morse is about one-fifteenth that of Thomson’s Mirror. Dot takes ’27 sec. at fifteen words per minute. 14. The weight of metal deposited from the