## Facts

- Eibel Process Co. owned a patent covering an improvement to Fourdrinier papermaking machines used to form paper from diluted pulp on a moving wire screen.
- At higher operating speeds, the stock initially moved slower than the wire, creating relative motion that caused disturbances at the critical forming point and produced uneven paper (e.g., streaks and ridges), limiting practical machine speed.
- The patented improvement substantially elevated the breast-roll end of the wire to create pitch so gravity increased stock speed, enabling stock velocity to approximate wire velocity at the critical point and reducing disturbances.
- The improvement was rapidly adopted in the industry and was claimed to materially increase output while improving sheet uniformity.
- Minnesota & Ontario Paper Co. operated machines with sufficient pitch to make gravity an appreciable factor in speed equalization; Eibel alleged infringement of claims 1, 2, 3, 7, 8, and 12.
- The district court granted injunctive relief and damages; the court of appeals reversed, finding the improvement an obvious use of gravity and directing dismissal.

## Issues

1. Whether substantially increasing wire pitch to use gravity to equalize stock and wire velocities at the critical forming point constituted patentable invention rather than an obvious application of a known principle.
2. Whether prior machines using slight pitch for different purposes, and alleged prior oral experiments, anticipated the claimed invention.
3. How the claims should be construed, including whether they required a particular angle or required pitch to be the sole means of equalizing speeds.
4. Whether the accused machines infringed under the proper construction.

## Decision

- The Supreme Court reversed the court of appeals and upheld the patent as valid.
- The Court rejected anticipation based on earlier slight-pitch uses directed to other objectives and found the asserted oral prior-discovery proof insufficient.
- The Court construed the claims liberally to cover machines where pitch is an appreciable factor (not necessarily the only factor) in bringing stock and wire speeds into approximate equality at the critical point.
- Under that construction, the Court held Minnesota & Ontario infringed claims 1, 2, 3, 7, 8, and 12.

## Legal Principles

- Discovering the cause of a persistent defect in an old machine and applying a concrete modification that remedies it can constitute patentable invention, even if the physical change is simple.
- A change characterized as an increase in degree may amount to invention when tied to a newly appreciated cause-and-remedy relationship and when it successfully cures a known defect.
- Prompt, widespread adoption and increased productivity may be strong evidence of novelty and utility.
- Prior use directed to a different and distinct purpose does not anticipate the later invention aimed at solving a different problem.
- Oral evidence offered to establish prior discovery must be clear and satisfactory to invalidate a patent.
- Accidental, unappreciated prior results do not constitute anticipation.
- A patent for a meritorious improvement that substantially advances the art is entitled to liberal claim construction.
- General descriptive terms are permissible where greater specificity is difficult and the disclosure enables skilled artisans to practice the invention.
- Novelty is not defeated because similar results could be achieved by different means.

## Conclusion

The Court sustained a patent on pitching a Fourdrinier wire so gravity appreciably accelerates stock to match wire speed at the critical forming point, treated the advance as inventive rather than a routine use of gravity, construed the claims broadly, and found infringement.


Eibel Process Co. v. Minnesota & Ontario Paper Co., 261 U.S. 45 (1923)