• The text in italics is copied from that url
• Immediate followed by some comments
In the last paragraph I explain my own opinion.

### Introduction

The article starts with the following sentence.
In other words, when the interferometer is at rest with respect to a nonrotating frame, the light takes the same amount of time to traverse the ring in either direction.
This is the case, when the interferometer is at rest under the condition that the speed of light is the same in all directions. In that case when a light flash is emitted from one corner in both directions, this flash will arrive simultaneous in the opposite corner.

### Reflection 1 - Comparision Sagnac Effect versus the behaviour of two Clocks

The bassic assumption of the Sagnac Effect is that the speed of light is the same in all directions.
1. In that case when the apparatus used is at rest, the arrival time of two pulses emmitted simultaneous in the bottom left corner, will be simultaneous in the top right corner. This is called apparatus #1
2. The same is true for apparatus #2 which is in linear motion relative to apparatus #1.
3. This is not true for apparatus #3 in rotation, relative to apparatus #1

The bassic assumption for a clock (working based on light signals) is also that the speed of light is the same in all directions.

1. When that is the case, two clocks #1 and #2 at rest will tick simultaneous or synchrone.
2. When clock #2 is moving relative to clock #1, clock #2 will run slower. This is also the case when accelerations are involved.
3. When a third clock is involved and both Clock #2 and clock #3 move with the same speed, in a straight line, in any direction their behaviour will be the same. This is also the case when accelerations are involved.
4. This is not the case when clock #3 is rotating around clock #2
For more information about the behaviour of clocks select this link: On the Electrodynamics of moving Bodies - by A. Einstein 1905 - Article review - Appendix 2

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Created: 12 January 2019

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