The **quadratrix** of Dinostratus was well known to the ancient Greek geometers, and is mentioned by Proclus, who ascribes the invention of the curve to a contemporary of Socrates, probably Hippias of Elis.

Then the locus of the intersection of PQ and OM is the **quadratrix** of Dinostratus.

The **quadratrix** of Tschirnhausen is constructed by dividing the arc and radius of a quadrant in the same number of equal parts as before.

Its properties are similar to those of the **quadratrix** of Dinostratus.

Thus Nicomedes invented the conchoid; Diodes the cissoid; Dinostratus studied the **quadratrix** invented by Hippias; all these curves furnished solutions, as is also the case with the trisectrix, a special form of Pascal's limacon.

The rest of the book treats of the trisection of an angle, and the solution of more general problems of the same kind by means of the **quadratrix** and spiral.

The invention of the conic sections is to be assigned to the school of geometers founded by Plato at Athens about the 4th century B.C. Under the guidance and inspiration of this philosopher much attention was given to the geometry of solids, and it is probable that while investigating the cone, Menaechrnus, an associate of Plato, pupil of Eudoxus, and brother of Dinostratus (the inventor of the **quadratrix**), discovered and investigated the various curves made by truncating a cone.