Pocketbook of Useful Formulæ and Memoranda
for Civil and Mechanical Engineers

321 OF ENGINEERING FORMULÆ. Telegraph Construction, by K. S. BbougH— continued. Let p — the pressure per unit of length of the wire. Then the strain on the wire at the insulator will be , /fl2 7d\ .------------- * = (sd + +^’ or If t' — the new strain on the wire and t — the original strain on the wire, then f - V^l + x t nearly. ELECTRICAL FORMULÆ, &c. By Paget Higgs, LL.D., C.E , and R. 8. Bkough. 1. Units. (Electromagnetic.) Ohm : Unit of resistance = 10" metre-second units. Volt: „ potential = 105 métre-gramme- second units. ■ quantity = 10~2 metre-gramme Webfr- ’ units- ■ i „ current = 10~2 metre-gramme- ( second units. Farad : „ capacity = 10-7 metre-second units.