Pocketbook of Useful Formulæ and Memoranda
for Civil and Mechanical Engineers

313 OF ENGINEERING FORMULA Telegraph Construction, by R. 8. Bkough . continued. Increment 'i of dip due I to small in- > crementof I length. J Elongation i of wire I from j straining. J d ~ Vf a (s — a) 8d=W s' = s fl + where Breaking strain per unit of area Modulus of elasticity per unit of area 57000 lbs. per sq. in. 25000000 lbs. per sq. in. = 0-0023. for soft iron wire Roughly, iron stretches about of Hs length within a strain of 1’ ton per square inch. When z — 4, 3 s' = 0 • 000575 s or about 2 ijnhes per 100 yards. Effect of 1 ture. J where f — the coefficient of dilatation. = 0-00Q01235 per 1°C, n — number of degrees through which temperature changes. e = reciprocal of modulus of elasticity. • = 0-00000004. In 100 yards epan the dip varies about 1 inch per G° Fall, change of temperatu ,e.