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Published online by Cambridge University Press: 03 November 2016
Let x0, y0, z0 be the areal coordinates of a particular point, x, y, z the areal coordinates of any other point. Put ξ =x - x0, etc. Then Σξ = 0, and ξ,η,ζ(or any two of them) serve to determine the position of a point, and a relation between them gives a locus.