1. Williamson, J. B. P., and Hunt, R. T., J. Phys., E, 1, 749 (1968).
2. Mallock, A., Nature, 117, 117 (1926).
3. Williams, G. H. H., and O'Neill, H., J. Iron and Steel Inst., 189, 29 (1958).
4. Bowden, F. P., and Tabor, D., Friction and Lubrication of Solids, 17 (Oxford Univ. Press, London, 1954).
5. Williamson, J. B. P., Proc. Symp. Interdisciplinary Approach to Friction and Wear, 85 (NASA, Washington, 1968).