The earlier of the moderns, for instance Fermat, Barrow, and others, who were the first to make use of infinitesimals in the application which was later developed into differential and integral calculus, and then Leibniz also and his followers, and Euler as well, have always openly believed that they were entitled to omit the products of infinitesimal differences, as well as their higher powers, simply on the ground that they vanish relative to the lower order.