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OF ENGINEERING FORMULÆ.
Loci. (Paget Higgs.)
Straight Line. — The locus of a point which
moves in a given direction, and so as to pass
through a given position.
Circle.—The locus of every point in a given
plane which is at a given distance from a given
point in that plane. The given point is the centre»
Ellipse.—The locus of every point in a plane
such that the sum of its distances from two given
points in that plane is equal to a given length.
This locus is called the ellipse; the two points its
foci.
Hyperbola.—The locus of every point in a plane
so situated that the difference of its distances from
two given points in that plane is equal to a given
length.
Parabola.—The locus of every point in a plane
which is equally distant from a given point and a
given straight line in that plane. The point is
the focus; given line the directrix.
It is useful to note that the square root of any
number may be constructed as the third side of a
right triangle, of which the hypotheuuse and one
leg are respectively the halves of the numbers
next above and next below the given number.
Also that Euclid’s Pons Asinorum appears more
usefully st i ted as that the square of a line is equal
to the num of the squares of its projections on two
rectangular axea.