Pocketbook of Useful Formulæ and Memoranda
for Civil and Mechanical Engineers

456 Molesworth’s pocket-book Compound Engines. A = Area of large cylinder. a — Area of small ditto. L — Length of stroke. I = Distance travelled by piston before steam is cut off in sipai 1 cylinder. P s= Initial pressure of steam in lbs. per square inch, including pressure of atmosphere. p — Blick pressure caused by imperfect vacuum - generally 2| lbs. per square inch. w — Work performed during I portion of stroke. W — Stroke work performed during whole stroke. N s= Number of revolutions of engine per minute. > . AL *E = Ratio of expansion = —— • / , a L 4- (A —a) l\ w = a P 111 + hyp. log. •---------— j —ApZ. W = A P L (1 + hyp. log. E) - ApL. Horse-power X -OOOOCOS ALN (1 + hyp. log. E) — pj • Hyp. log. indicates the hyperbolic logarithm. (See Table of Hyperbolic Logarithms.) Tue hyperbolic logarithm of any number is found by multiplying the common logarithm of the number by 2’302585. Y The limit of useful expansion is to 5 lbs. per square Inch, including atmosphere.