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[From the Proceedings of the London Mathematical Society, vol. n. (1866—1869), 
pp. 6—7, 25—26, 29, 61—63, 103—104, 123—125.] 
December 13, 1866. pp. 6—7. 
Piiof. Cayley exhibited and explained some geometrical drawings. Thinking that 
the information might be convenient for persons wishing to make similar drawings, he 
noticed that the paper used was a tinted drawing paper, made in continuous lengths 
up to 24 yards, and of the breadth of about 56 inches 0; the half-breadth being 
therefore sufficient for ordinary figures, and the paper being of a good quality and 
taking colour very readily. Among the drawings was one of the conics through four 
points forming a convex quadrangle. The plane is here divided into regions by the 
lines joining each of the six pairs of points, and by the two parabolas through the 
four points; and the regions being distinguished by different colours, the general form 
of the conics of the system is very clearly seen. (Prof. Cayley remarked that it would 
be interesting to make the figures of other systems of conics satisfying four conditions; 
and in particular for the remaining elementary systems of conics, where the conics pass 
through a number 3, 2, 1 or 0 of points and touch a number 1, 2, 3 or 4 of lines: 
the construction of some of these figures is, however, practically a great deal more 
difficult.) Other figures related to Cartesians and Bicircular Quartics. One of these 
was a figure of a system of triconfocal Cartesians; and derived from this by inversion 
in regard to a circle, there was a figure of a system of quadriconfocal bicircular 
quartics: in the assumed position of the inverting circle, each quartic consists (like 
the Cartesian which gives rise to it) of an exterior and an interior continuous curve, 
and the general aspect of the figure is that of a distortion of the original figure of 
the Cartesians. Another figure was that of the bicircular quartic, for which the 
1 Sold at Messrs Lechertier-Barbe’s, Regent Street, at Gd. per yard, or 9s. the piece. 
3—2