Discussion: “The Present State of Lubrication and Its Relation to Rheology” (Appeldoorn, J. K., 1968, ASME J. Lubr. Technol., 90, pp. 526–530) and “The Significant Rheological Characteristics of Lubricants” (Metzner, A. B., 1968, ASME J. Lubr. Technol., 90, pp. 531–539)