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We may remember the fact, that in a moving system we always have to understand by x, y, z the coordinates with respect to the axes that share the translation.

If the magnitudes (70) are known as functions of x, y, z and t' , thus also as functions of x, y, z and t, then ${\mathfrak {D}}_{x},{\mathfrak {D}}_{y},{\mathfrak {D}}_{z},\ {\mathfrak {H}}_{x},{\mathfrak {H}}_{y},{\mathfrak {H}}_{z}$ can be calculated fron the equations (IX) and ($VI_{c}$).

Different applications.

§ 60. We want to call the two states of motion — in the stationary and in the moving system of bodies —, of which we have spoken so far, corresponding states. Now, they shall be mutually compared more precisely.

a. If in a stationary system the magnitudes (69) are periodic functions of t with the period T, then in the other system the magnitudes (70) have the same period with respect to $t'$, thus also with respect to t, when we let x, y, z remain constant. When interpreting this result, we have to consider, that two periods must be distinguished in the case of translation (see §§ 37 and 38), which we accordingly can call absolute and relative period. We are dealing with the absolute one, when we consider the temporal variations in a point that has a fixed position against the aether; but we are dealing with the relative one, when we consider a point that moves together with ponderable matter. The things found above can now be expressed as follows:

If a state of oscillation in the moving system shall correspond to a state in the stationary system, then the relative oscillation period in the first mentioned case must be equal to the oscillation period in the second mentioned case.

b. In the stationary system, no motion of light may take place at an arbitrary location, i.e., ${\mathfrak {D}},{\mathfrak {E}}$ and ${\mathfrak {H}}$ may vanish at this place. At the corresponding location of the moving bodies it is consequently ${\mathfrak {D}}'=0,{\mathfrak {E}}=0,{\mathfrak {\mathfrak {H}}}'=0$, thus also ${\mathfrak {D}}=0,{\mathfrak {H}}=0$, so that at this place the motion of light is missing as well.

From that it directly follows, that a surface that forms the border of a space filled with light within a stationary body,