"You probably forget the important difference between a directrix and an axis," hotly observed Barbican.
directrix, a fixed line that is required for the description of a curve.
The centre of a circle is its focus, and its directrix has gone to infinity, having no special direction.
If a parabola roll on another parabola, their vertices coinciding, the focus of the first traces out the directrix of the second.
Similarly, in an hyperbola a vertex is nearer 704 to the directrix than to the focus.
The surface formed by revolving the catenary about its directrix is named the alysseide.
As necessary as the directrix is to the curve, so are the corresponding laws to the State.
The only surface of revolution having this property is the catenoid formed by the revolution of a catenary about its directrix.
With your permission I will add a few words to those I have already uttered with regard to the directrix.
Since the tension is measured by the height above the directrix these two catenaries have the same directrix.