Introduction to Earth Sciences I
1.1 The Earth's Size and Shape, continued
Because of this he knew about angles. At that time the concept of "angle" was still new and it was cast in terms of ratios in two different ways.
Erastosthenes measured the sun angle on the longest day at midday using the shadow cast by a vertical stick -- a triangle made by a vertical stick in the ground and the length of the shadow it cast.
