A helix is a curve in three dimensions, the tangent to which makes a constant angle
with a fixed line. A circular helix is formed by winding
a line around a cylinder so the radius
is always the same. A conical helix is formed by winding
a line around a cone, so that, consequently,
its radius constantly changes. Springs often take the form of various kinds
of helices. In nature, the DNA molecule is in
the shape of a double helix.
|A circular helix (right) and cylindroconical helix
(left). In each case the curve (red) makes a constant angle with the
elements (e.g., the blue lines) in the surface on which it is draw.