Circles of these radii are usually marked around the jack for convenience' sake.
The resistance to motion round a curve has not been so systematically studied that any definite rule can be formulated applicable to all classes of rolling stock and all radii of curves.
Thus, while halos have certain definite radii, viz.
Let v be the common velocity of the two pitch-circles, ri, C2, their radii; then the above equation becomes /1 I
It may be readily shown that the external and internal centres are the points where the line joining the centres of the two circles is divided externally and internally in the ratio of their radii.
