The classical theories of Linear Elasticity and Newtonian Fluids, though trium phantly elegant as mathematical structures, do not adequately describe the defor mation and flow of most real materials. Attempts to characterize the behaviour of real materials under the action of external forces gave rise to the science of Rheology. Early rheological studies isolated the phenomena now labelled as viscoelastic. Weber (1835, 1841), researching the behaviour of silk threats under load, noted an instantaneous extension, followed by a further extension over a long period of time. On removal of the load, the original length was eventually recovered. He also deduced that the phenomena of stress relaxation and damping of vibrations should occur. Later investigators showed that similar effects may be observed in other materials. The German school referred to these as "Elastische Nachwirkung" or "the elastic aftereffect" while the British school, including Lord Kelvin, spoke ofthe "viscosityofsolids." The universal adoption of the term "Viscoelasticity," intended to convey behaviour combining proper ties both of a viscous liquid and an elastic solid, is of recent origin, not being used for example by Love (1934), though Alfrey (1948) uses it in the context of polymers. The earliest attempts at mathematically modelling viscoelastic behaviour were those of Maxwell (1867) (actually in the context of his work on gases; he used this model for calculating the viscosity of a gas) and Meyer (1874)."

Principles of Patent Law provides comprehensive coverage of the policies, laws, rules, and practices of the U.S. patent system in a format accessible to students, lawyers, government officials, and business people. The Seventh Edition builds on the strengths of prior editions in combining discussions of the law and theory of patents with instructive case materials. The Seventh Edition features a number of significant changes designed to reflect the "new normal" with respect to various aspects of U.S. patent law, including (1) the revitalization of jurisprudence on subject-matter eligibility, (2) the ongoing transition to dominance of patentability provisions adopted by the America Invents Act of 2011 (AIA), and (3) the increased roles of administrative proceedings and administrative-law concerns in patent law practice. In response to such developments, we have reorganized the chapters on patentability essentially to follow the order of 101 to 103 and 112 in the Patent Act. In the chapters on novelty and nonobviousness, we have generally placed the primary focus on the AIA formulations of these requirements, with pre-AIA law now tending to appear in a more secondary role. We have also introduced a new, separate chapter on "Procedures and Institutions" of patent law. We hope that the result is a spryer casebook that stays true to the vision of the First Edition.