C 
138 ON THE SYSTEM OF CONICS WHICH PASS THROUGH THE SAME FOUR POINTS. [190 
Fig. B'. Two real and two imaginary points, the real centre of the quadrangle 
lying between the real points. There are no parabolas, and the system contains only 
hyperbolas. 
B' 
Lastly, when the four points are imaginary. We have here only a single case. 
Fig. G. Four imaginary points. The points lie on two real lines, there are (besides 
the point of intersection of these lines) two other real centres of the quadrangle, which 
lie harmonically with respect to the two lines. The system contains two parabolas 
and these and the two lines divide the plane of the figure into four regions, two of 
which contain each of them ellipses, and the other two contain each of them hyperbolas.