635
OF ENGINEERING FORMULÆ.
Conic Sections.
Diagrams and Formulæ corresponding with the Symbols
are given in succeeding pages.
Symbol. DEFINITION.
A Major Axis (or Transverse Axis; is the ;
right line that passes through the vertices
of a curve (Figs. 1, 2, 3). .
a Minor Axis (or Conjugate) is a right line
passing through the centre of the majoi
axis at right angles to it. In the parabola
A and a are infinite; the symbols have
therefore been adopted to express the
height and i the base respectively in the
case of the parabola.
B Slant Height of the portion of the cone
that affects the figure (see Diagrams 3, 4,
and 5).
C and c Diameters of the Cone at the respective
vertices of the figure (Figs. 4, 5, and 6).
D Diameter of Curve is any straight line
that passes through the centre of the
curve and is terminated at both ends by
the circumference (Fig. 7).
<1 . Conjugate üiamkter to D.—A diameter is
said to be conjugate tu another when it is
parallel to tbe tangent of that diameter.
F Distance of Foci apart (Figs. 8 and 11).
f Focal Distance, or distance of tbe focus
from the nearest vertex (Figs. 8 and 11).
a Distance of Vertex from Directbix.—
The directrix is a line at right angles to
the major axis, and is in such a position
that f’,gv.y : G (Fig. 9)-
G Offset to Directrix from the end ot any
radius vector V (Hg. 9).
L Latus Rectum (or Principal Parameter)
passing through the focus, it is a double
ordinate, which is a third proportion to
the axis; or A: a :: 1L 8).