Published online by Cambridge University Press: 20 January 2009
In the Proceedings of the London Mathematical Society, Ser. 2, Vol. 20 (1921), pp. 465–489, Professor H. W. Turnbull has studied the projective invariant theory of three quadrics. The following paper is based on this work and develops one definite section of the theory. From the geometrical point of view the linear complex is now seen to be fundamental in the study of three arbitrary quadrics; particularly when their (2, 2, 2) invariant φ123 vanishes.
* φ123=0 when the three quadrics can be expressed as the sum of the same five squares (Toeplitz, Math. Annal., XI.)
* Cf. Proc. Lond. Math. Soc., loc. cit., p. 483. Type 9 on this table is reducible. Proc. Land. Math. Soc. Vol. 22. Series 2. Records p. iii. (1923).
* This denotes that the form is reducible.