FACTORS DETERMINING INFRINGEMENT
Early practice in the United States was to describe the invention in the specification of the patent and then claim the invention in general terms often "substantially as herein described" (an omnibus claim). As time went on, ever-increasing emphasis was placed on the language of the claims as the measure of the exclusive rights conferred by a patent. The question of infringement moved from one of whether the defendant's device embodied the plaintiff's invention to one of whether the claims of the patent, fairly construed, read on the defendant's device. Thus, a claim is a definition of an invention. It is an abstraction of an indefinite number of physical objects. The number which the claim will read on is its scope or breadth.
Winans v. Denmead ( 1853) was the first decision to use the Doctrine of Equivalents to do serious damage to the literal meaning of the language of the patent claim. The defendant constructed railroad cars for the carrying of coal that were "octagonal and pyramidal" in shape, rather than "cylindrical and conical" of the invention, which were "in the form of the frustum of a cone." In a 5-to-4 decision, the Supreme Court held that the defendant substantially embodied the invention, and thereby obtained the same kind of result as was reached by the invention.
After the Patent Act of 1870, the Supreme Court placed increased emphasis on the language of the claims as the measure of the exclusive rights granted by a patent. Despite this new emphasis on claim language, Winans and the Doctrine of Equivalents survived as a tool of interpretation. Further, the range of allowable equivalents was said to depend upon and vary