2 Pappus, Mathematicae Collectiones, vii, 129.

3 J. Verneri, Libellus super vigintiduobus elementis conicis, etc.

1522.

4 Kepler, Ad Vitellionem paralipomena quibus astronomiae pars optica traditur. 1604.

5 Desargues, Bruillon-project d'une atteinte aux evenements des rencontres d'un cone avec un plan. 1639. Edited and a.n.a.lyzed by Poudra, 1864.

6 The term 'pole' was first introduced, in the sense in which we have used it, in 1810, by a French mathematician named Servois (Gergonne, _Annales des Matheematiques_, I, 337), and the corresponding term 'polar' by the editor, Gergonne, of this same journal three years later.

7 Euler, Introductio in a.n.a.lysin infinitorum, Appendix, cap. V. 1748.

8 uvres de Desargues, t. II, 132.

9 uvres de Desargues, t. II, 370.

10 uvres de Descartes, t. II, 499.

11 uvres de Pascal, par Brunsehvig et Boutroux, t. I, 252.

12 Chasles, Histoire de la Geometrie, 70.

13 uvres de Desargues, t. I, 231.

14 See Ball, History of Mathematics, French edition, t. II, 233.

15 Newton, Principia, lib. i, lemma XXI.

16 Maclaurin, Philosophical Transactions of the Royal Society of London, 1735.

17 Monge, Geometrie Descriptive. 1800.

18 Poncelet, Traite des Proprietes Projectives des Figures. 1822. (See p. 357, Vol. II, of the edition of 1866.)

19 Gergonne, _Annales de Mathematiques, XVI, 209. 1826._

20 Steiner, Systematische Ehtwickelung der Abhangigkeit geometrischer Gestalten von einander. 1832.

21 Von Staudt, Geometrie der Lage. 1847.

22 Reye, Geometrie der Lage. Translated by Holgate, 1897.

23 Ball, loc. cit. p. 261.