This problem, also termed the " Apollonian problem," was demonstrated with the aid of conic sections by Apollonius in his book on Contacts or **Tangencies**; geometrical solutions involving the conic sections were also given by Adrianus Romanus, Vieta, Newton and others.

The other treatises of Apollonius mentioned by Pappus are - 1st, Aayov alroropii, Cutting off a Ratio; 2nd, Xcopiov a7rorop, Cutting off an Area; 3rd, Ocwpui j Av i Tog, Determinate Section; 4th, 'Eiraci)aL, **Tangencies**; 5th, 11-€1,o-as, Inclinations; 6th, Tinrot bri ret50t, Plane Loci.

In the same volume are treatises on "Geometric Loci, or Spherical **Tangencies**," and on the "Rectification of Curves," besides a restoration of "Apollonius's Plane Loci," together with the author's correspondence addressed to Descartes, Pascal, Roberval, Huygens and others.