# Some special nets of quadrics in four-dimensional space

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## Keywords

Secant Plane Double Curve Quartic Surface Quartic Curve Jacobian Curve
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## References

- 1.«The geometry of a net of quadries in four-dimensional space».
*Acta mathematica*64 (1935), 185–242. This paper will be referred to as*G.N.Q.*Google Scholar - 1.If we have, on a ruled surface of order
*n*, a curve of order*m*meeting each generator in*k*points and such that*s*generators pass through each point of the curve, and also a curve of order*m*′ meeting each generator in*k*′ points and such that*s*′ generators pass through each point of the curve, then the number of intersections of the two curves is*msk′+m′s′k−nkk′*Google Scholar - 1.See, for a corresponding argument in [3],A. C. Dixon,
*Proc. London Math. Soc.*(2), 7 (1909), 153.Google Scholar - 1.This follows immediately also from the existence of the line-cones {
*P*}. The tangents ofϑ at its three intersections with a trisecant are cospatial because, it*P*is any one of the intersections of the trisecant withϑ they lie in the solid which touches {*P*} along the plane joining the trisecant to the tangent ofϑ at*P*. The four tacnodes of the plane projection ofϑ are on conic which touches the four tacnodal tangents.Google Scholar - 1.We shall assume as known the properties of the rational quartic curve and of loci associated with it; for example the loci generated by its tangents, by its chords and by its osculating planes. Many of these properties can be obtained very simply either from the projective method of generating the curve or from its parametric representation (equivalent to the above) first given by Clifford.Google Scholar
- 1.For the order of a locus given by the vanishing of the determinants of a matrix see Salmon:
*Higher Algebra*(Dublin, 1885), Lesson 19.Google Scholar - 1.See, for example, Veronese,
*loc. cit.*, 202.Google Scholar - 1.See, for example, Room:
*Proc. London Math. Soc.*(2) 36, 1934, 12–15.Google Scholar - 1.
*Proc. London Math. Soc.*(2), 30, 1930, 305.Google Scholar - 1.We need not consider the possibility of the trisecant being a generator of more than one of the three cones. The only chords ofϑ which are generators of two cones are the 120 lines which are chords both ofϑ and of the base curve of the net, and none of these is a trisecant ofϑ.Google Scholar
- 1.
*G.N.Q.*§ 16.Google Scholar - 1.Concerning the Segre primal and its associated hexahedron see Castelnuovo:
*Atti Ist. Veneto*(6), 6 (1888), 547–565.Google Scholar - 1.
*Math. Annalen*7 (1874), 308.Google Scholar - 2.
*Proc. London Math. Soc.*(2), 36 (1933), 25–26.Google Scholar

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© Almqvist & Wiksells Boktryckeri-A.-B. 1936