  We have defined slowness (or reciprocal velocity, corresponding to velocity
v) as cc/v, where c is the speed of light. It is observed that the relative
velocity remains invariant if the velocities are replaced by corresponding
slownesses i.e. relative motion in one dimension is reciprocal symmetric.
Reciprocity operation, which converts a velocity to the corresponding slowness,
is found. Lorentz transformation is generalized so that Lorentz invariance is
maintained if velocities are replaced by corresponding slownesses.
