Pocketbook of Useful Formulæ and Memoranda
for Civil and Mechanical Engineers

642 MOLESWORTH’S POCKET-BOOK Ellipse—continued. To draw an Ellipse: # From n, with radius n F = semi-transverse axis k m, draw a circle, cutting the transverse axis at F F'. F F’ are the foci of the ellipse. On the transverse axis lay off any points abed, between the foci, and . _ From F with radius = p a describe a portion of a circle at e, also from F' with radius = m a describe a portion of a circle at e; the curve will pass through the intersection of these circles at e.. In like manner f is described from the foci with the radii = pb and m b respectively g with „ = pc „ me „ h ,, „ — p d „ m d „ To Calculate any Ordinate (see diagram next page). Let T — Semi-transverse axis. C = Semi-conjugate axis. K — The length of any ordinates. X = Distance of the ordinate from the centre. Area of an ellipse = TC3-1416. Periphery of an ellipse approximately — i w[V2(T=^rC4) + T + c] + 0-2078 (T - C).