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Published online by Cambridge University Press: 20 January 2009
1. This paper contains a number of investigations, more or less connected, on the theory of systems of circles. In such a well-worn field one does not expect to have hit upon much that is absolutely new, but it may be hoped that there is sufficient freshness of treatment to give the paper some interest even where it deals with results already known.
* See Art. 16 below.
* Conversely, if (3) is satisfied, the circles 1, 2, 3, 4 have a common tangent cirole. To prove this, take the circle 5 so that 152=252=352=0. The equation (1) is a quadratio for 452, one of the roots of which is zero, in virtue of (3). Hence one of the two circles touching 1, 2, 3 touches 4 also.