## Facts

- Ross Winans obtained a patent for an improvement in railroad cars used to transport coal.
- The patented car body used sheet iron construction with an upper cylindrical portion and a lower portion “in the form of a frustum of a cone,” with a flange at the lower edge and a movable bottom.
- Winans’s design aimed to lower the center of gravity and increase carrying capacity by allowing the lower part of the car body to extend down within the truck frame and between the axles.
- The design also sought to distribute the load’s pressure more evenly around the car body so the structure resisted deformation under heavy coal loads.
- Adam, Edward, and Talbot Denmead manufactured coal cars with an octagonal (rectilinear) body rather than a circular conical form.
- Winans sued the Denmeads for patent infringement in the Circuit Court for the District of Maryland.
- The trial judge instructed, in substance, that the patent protected conical bodies but did not reach rectilinear bodies, and the jury returned a verdict for the Denmeads.
- Winans sought Supreme Court review by writ of error.

## Issues

1. Whether a patent claim describing a coal-car body “in the form of a frustum of a cone” is confined to a strictly circular frustum, or can cover other shapes (such as an octagon) that operate in substantially the same way to achieve substantially the same result.
2. Whether, once the patent is properly construed, the question of infringement by an asserted equivalent is generally a question for the jury rather than resolved by a categorical, form-based instruction.

## Decision

- The Supreme Court reversed the judgment for the Denmeads and remanded for further proceedings.
- The Court held that the patent was not necessarily limited to the exact geometric outline of a perfect circular frustum where the accused structure used substantially the same means, working in substantially the same way, to obtain the same result.
- The trial court erred by treating the conical-versus-rectilinear distinction as controlling as a matter of law, which removed from the jury the factual inquiry into equivalence.
- With a correct construction of the patent, whether the Denmeads’ octagonal cars were substantially the same as Winans’s invention was for the jury to decide.
- Chief Justice Taney and Justices Catron, Daniel, and Campbell dissented.

## Legal Principles

- Patent protection is not always confined to literal form when the invention, fairly read from the claim and specification, is directed to a practical way of producing a result through a particular operation of mechanical principles.
- An accused device may infringe even without literal identity if it is substantially equivalent—commonly described as achieving substantially the same result in substantially the same way by substantially the same means.
- Claim construction is for the court, but once the patent is correctly construed, infringement based on substantial equivalence commonly presents a factual question for the jury.
- A patentee’s rights cannot be avoided by minor or colorable changes in shape that copy the substance of the patented improvement.

## Conclusion

Winans v. Denmead holds that a patent claim describing a conical-frustum coal car body was not automatically limited to a perfectly circular cone; if an octagonal car employed substantially the same arrangement and operation to obtain the same practical advantages, it could infringe, and the jury should decide that equivalence after the court gives a proper construction of the patent.


Winans v. Denmead, 56 U.S. 330 (1853)