抄録
In this paper we present three matters. First we show that the cross sections of two circular cones, which are the spatial curve of the ovals of Descartes, can be defined by three dimensional parametric formula. These formula were derived so that we can easily obtain the perspective drawings of the spatial curve with computer graphics. Secondly, we present that the ovals can be defined by orthopoles that satisfy some conditions. This defintion indicates the geometrical composition of the ovals, and we present its proof. Finally, we describe the method to draw the normal line of the ovals and also give its proof. Thus additional new properties on the ovals are shown.
