During a transverse acceleration of a light clock from rest, the mirrors must be tilted so as to retain the light pulse. The mirrors therefore have a normal velocity which increases the frequency of the pulse at each reflection. If a mirror is annihilated, the frequency of the escaping pulse, as a result of many reflections, is that of the relativistic Doppler effect. This holds for any acceleration, if the Fitzgerald contraction is assumed, thereby furnishing a new mechanism for such frequencies. The traditional mechanism, in which the source (subject to the time dilation) generates a pulse modulated by the source motion, is therefore not a unique explanation of the Doppler effect. The new mechanism permits the speculation that radiation preexists in atomic sources, rather than being generated at the instant of release.