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The introduction of the substitutions (10), (12) or (13) always gives, if *δ* is given by the constraints along a given surface as an arbitrary function of time, the transition from the effect of a stationary source to the effect when it is in translational motion.

If, for example, we have on a very small sphere of radius *R*, then the propagated dilation is given by:

The substitution (10) gives the influence of a translation of a "sounding" sphere parallel to the *X*-axis. The discussion of the result is equivalent to that employed under 3).