this follows from the second of equations (29) and shows that the clock goes slower than if it were at rest relatively to
'. These two consequences, which hold, mutatis mutandis, for every system of reference, form the physical content, free from convention, of the Lorentz transformation.
Addition Theorem for Velocities. If we combine two special Lorentz transformations with the relative velocities
and
, then the velocity of the single Lorentz transformation which takes the place of the two separate ones is, according to (27), given by
