This is a page from “Letters of Euler to a German Princess, on Different Subjects in Physics and Philosophy”, written by Leonhard Euler.
Which part is the illustration, and which is the main text? As you can see the demonstration of Eulero is strongly based on the succession of graphics elements.
In the first printed version (in french) it is possible to see how deeper was the relation between alphabetic text and diagrammatic text. It could be interesting to see which was the relation between elements in the original manuscript.
Leonardo Romei & Luciano Perondi
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Sinsemia 