Note 86 — Chapter XXVI · TENSORS AND THE LAWS OF NATURE

If the spatial mesh-system we are considering is one of straight lines, a Cartesian one, for example, the statement in the text is accurate, but if we consider the more general case of a curvilinear mesh-system, we must introduce certain restrictions. In this last instance, our rod must be of infinitesimal length, for were its length finite, its orientation as referred to the curvilinear mesh-system would vary from place to place. This would introduce complications. Hence it is preferable to restrict our attention to rods of infinitesimal length and consider orientation as defined at a point. With this restriction in force, there is nothing to change in the explanation given in the text.