Page:American Journal of Mathematics Vol. 2 (1879).pdf/17

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Ladd, The Pascal Hexagram.
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in this hexagon, is the reciprocal of the conic with respect to a third conic; twelve points of which may be obtained by taking on each side of the Brianchon hexagon the two points which form a harmonic range with each of the two pairs of vertices on this side; for instance, on the two points which are harmonic at once with and with The hexagon is the reciprocal with respect to the conic of the hexagon formed by joining its alternate vertices; the point is the pole of the line the point is the pole of of the line hence the Pascal is the polar of the point is the pole of is the pole of hence the Pascal is the polar of the point It follows that the intersection of the Pascals which is the Kirkman is the pole of a line joining to which is the Pascal But the six hexagons, form, by connectors of alternate vertices, a Brianchon hexagon composed of the same sides in different orders, and hence circumscribed to the same conic, therefore the six Pascals are the poles of the six Kirkmans with respect to the same conic Moreover, the points and in which the first three and the second three Pascals intersect are the poles respectively of the lines and which connect the first three and the second three Kirkmans. The two points in question are harmonic conjugates with respect to the conic hence their polars with respect to the lines of the same notation, are harmonic conjugates with respect to the reciprocal conic, The triangle whose vertices are two corresponding points and the intersection of the lines through them (or, what is the same thing, the triangle whose sides are two corresponding lines and the line joining the points on them) is a triangle self-conjugate with respect to the conic two of its vertices being at the same time conjugate with respect to and two of its sides with respect to Since this conic, is inscribed in the triangles and we shall call it the conic (where the order of the letters in each group of three is of no consequence) and the conic with respect to which it is the reciprocal of we shall call There are ten conics the