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Published online by Cambridge University Press: 24 October 2008
The locus of a point the feet of the perpendiculars from which on the faces of a tetrahedron are coplanar is known to be a cubic surface having nodes at the corners: the pedal planes, by which I mean planes containing the feet of four perpendiculars, do not seem to have been much discussed. I propose to prove two theorems concerning them and make some remarks on their envelope.
* See, for example, Richmond, , Camb. Phil. Soc. Proc., Vol. XXII. p. 35.Google Scholar
* Cf. the preceding paper § 3. The quadric has triads of perpendicular generators and its linear metrical invariant vanishes.
* The argument will be made clear by considering the analogy in two dimensions.
† Cf. § 3 of the preceding paper.
* Rohn, , Math. Ann. vol. 24 (1884), p. 55.CrossRefGoogle Scholar
* Cf. Somerville, , Proc. International Congress, Cambridge, 1912.Google Scholar