"This quantity \iint uydxdy was termed the relative resistance of the beam or the resistance of the base of fracture. ...it is necessary to know u before we can make use of it. He then proceeds to apply it to Galilei's and the Mariotte-Leibniz hypotheses."
https://en.wikiquote.org/wiki/A_History_of_the_Theory_of_Elasticity_and_of_the_Strength_of_Materials