Good and evil, right and wrong, become infinitesimal, ephemeral matters.
In mechanics we are specially concerned with the theory of infinitesimal displacements.
It thus appears that an infinitesimal rotation is of the nature of a localized vector, and is subject in all respects to the same mathematical Jaws as a force, conceived as acting on a rigid body.
Let us conceive the zone in question to be divided into infinitesimal rings of equal area.
In the notation of the integral calculus, this area is equal to f x o udx; but the notation is inconvenient, since it implies a division into infinitesimal elements, which is not essential to the idea of an area.