Definition VI.
THey called also a certain line EL (Fig. 101.) by the name of Latus Rectum, which is particularly to be found in all the sections, as we shall hereafter shew: And be∣cause this Latus Rectum is a sort of a Rule or Measure, ac∣cording to which the squares or powers of the ordinates used to be estimated or valued (as we will shew in its proper place) therefore the Ancients used to call it by a Periphrasis Linea se∣cundum quam possunt Ordinatim applicatae, or the measure of the powers of the Ordinates; by some latter Authors it is cal∣led the Parameter. Now a mean proportional PQ found be∣tween this Latus Rectum and the Latus Transversum (Fig. 104 n. 1. and 2) (see also hereafter Consect. 2. Prop. 8.) and drawn thro' the centre O parallel to the Ordinates is cal∣led the second Axis or Diameter, or the Conjugate of the Hy∣perbola.