158] PLANE REPRESENTATION OF DYNAMICAL PROBLEMS. 145 



frequently be found that the geometrical theory assumes some extreme and 

 uninteresting type. For instance, a case often quoted as an illustration of 

 two degrees of freedom, is that of a body free to rotate around an axis, 

 and to slide along it. The representative circle has then an infinite 

 radius, and the finite portion thereof is merely a ray perpendicular to the 

 axis of pitch. The geometrical theory then retains merely a vestige of 

 its interest. 



B. 10 



