Calculation of the circumference of the Earth:
We heard the results of the schools in Alexandria .We have also heard the results of the schools in Aswan. We must speak now: “20°40' for a latitude of 44°08' north.” The most important observation is far away from Alexandria: 72 km in the south of Aswan. Exactly on the Tropic of Cancer (2296 km in the south of Lafrançaise). This observation is the start of the summer. When it is solar midday, the solar rays are coming straight down from the vertical. At this place, at this moment, there is no shade.