^{Page 178 of note*} If r be the radius of either wheel, θ its inclination to the vertical when the car is travelling in a straight line and ϕ the angular deviation of the path of the wheel from this line, the vertical height of the centre of the wheel above the ground is given by the expression r cos θ/√(1-sin² θ sin² ϕ), which represents a steadily increasing even function of ϕ. It follows that, when the car is steered round a bend, the height of the front axle is slightly increased, and hence, owing to the effect of gravity, the car will tend to “straighten out” automatically after the turn.