144 
DEVELOPMENTS ON THE PORISM, &C. [128 
Thus, in the figure (which is simply Sir W. R. Hamilton’s figure 81 put into 
perspective), the system of relations 
F, G(..)ABCI, 
G, H{..) BCDK, 
H, I (..) CDEF, 
I, K (..) BE AG, 
K, F(..) EABH, 
will mean, F, G (..) ABCI, that there is a conic inscribed in the quadrilateral ABGI 
such that the tangents to this conic through the points F and G pass two and two 
through the points of contact of the circumscribed and the inscribed conics, and 
similarly for the other relations of the system. As the figure is drawn, the tangents 
in question are of course (as the tangents through the foci in the case of the two 
concentric circles) imaginary. 
2 Stone Buildings, March 7, 1854.