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3. The work of Sagnac is therefore of very great importance.

Now, I'm not in the least thinking about casting doubt on the experimental part of the work, on the contrary, I consider the method itself of being capable to be further developed in different directions.

On the other hand, the theoretical foundations and consequently also the conclusions, not necessarily require the interpretation given by Sagnac.

4. I allow myself, to reproduce the basic idea of the experimental arrangement in a somewhat schematic form, with the note that the state of matter itself is not changed by that.

A sphere of radius $r$ shall be given (Fig. 1), which is reflecting at the interior side.

At one point $O$ of the rim, a light ray is split; part $R$ is circulating clockwise, the other part $L$ counter-clockwise.

Both parts follow the same polygon which is closed by one circulation (an octagon in Fig. 1)

If $U$ denotes the circumference of the polygon, then the same $U$ is thus the light path for both rays; the circulating time is:

$T={\frac {U}{c}}$,

both rays simultaneously arrive in $O$ again.

Now we think of observation point $O$ as having the translatory velocity $v$; namely this shall happen by rotating the circle with rotating number $N$, thus it shall be:

$v=2\pi \cdot N\cdot r\,$

Equally well^[1], one also can think of point $O$ and the whole circle as being held at rest, then at every location $O$ as well as at any boundary point of the circle there is a oppositely

1. G. Sagnac, l.c., p. 709 u. 1411.