Pocketbook of Useful Formulæ and Memoranda
for Civil and Mechanical Engineers

312 MOLESWORTH’S POCKET-BOOK Telegraph Construction, by R. S. IJbOUGJI - continued. ' and that (2) the dip varies approximately as the square of the length of the span. Roughly, for iron wire, For maximum span d = a 3’ Strain at Insulator. Given a and d, required I, I c + d. Approximately, a2 Id ~ 8rf + IT = É”“rly' Angle at Insulator.* Length of wire in span.f / . a , a3 a5 tau-J-^ + 48'c3 + 3840^+ ”• Approximately, . 3 a tau.« =i--------------- 2a/ (3Cy-3gy 4<Z , = — nearly. ( cP s = a 4-------k ----4-... £ 24 <? T 1920 é r ‘ Approximately, s = "\/a2 + d2 3 8 cP , = a + nearly. 3a * * Can be measured by the “ inclinometer ” or “ batter level." lu 100 yards spau the wire is about J inch longer than