Is the Flat Vault a Lost Proposition in John Wallis’s Work?

At first glance, proposition X of Chapter VI, dedicated to the lever, in the third part of the Mechanica: sive De Motu Tractatus Geometricus published in 1670 by John WallisWallis, John, seems completely disconnected from the work as a whole. Its title shows clearly that this is a question of architecture. This domain is, however, completely absent from Wallis’s rich yet varied work, except through the study of the instruments for lifting or hoisting, which are the main tools of architecture and whose study has provided the foundations of statics, The aim in the present chapter is, on the one hand, to understand the work done by WallisWallis, John with this proposition X and, on the other, to try to understand what attracted him to this very particular problem. Along the way, Jean Truchet’sTruchet, Jean (Père Sébastien) work on flat vaults is also examined.