David A. Watt ; with a contribution by Muffy Thomas. Robert G. Sutter ; with a contribution by Larry Niksch. David A. Watt ;with contributions by William Findlay, John Hughes. Philip Ball ; with a contribution by Dirk Helbing. by Michael Liebman ; with a contribution by Rina Tadmor. E. D. Dorrell ; with a contribution by J. R. O. Collin. Hans Kelker, Rolf Hatz ; with a contribution by Christian Schumann. Mary Lou Moore, with a contribution by Ora Strickland. Josef Novak ; with a contribution by Piet A. Leclercq.