The Roller Mill Patent case is a landmark 1894 legal dispute that dealt with the issue of patent rights and inventions. The case revolved around inventor John C. Leidigh, who had patented an improvement to roller mills - machines used in flour production. However, another company called Washburn & Moen Manufacturing Company began using a similar design without his permission, leading to Leidigh suing them for patent infringement. The Supreme Court ruled against Leidigh stating that he could not claim exclusive rights over the concept of roller mills as they were already widely known and used before his supposed invention. His improvements were deemed minor adjustments rather than significant innovations deserving of a new patent protection. This ruling set an important precedent in American law by clarifying what constitutes as an 'invention' under U.S patent laws: it must be significantly different from existing technology or knowledge at the time of its creation.

The dissenting opinion in the Roller Mill Patent case argued that the patent should be upheld. The justices disagreed with the majority's view that there was a lack of novelty and invention in LePage's design for a roller mill. They contended that while individual components of his machine were not new, their combination into an efficient, effective milling device constituted sufficient innovation to warrant patent protection. Furthermore, they pointed out that LePage’s mill had been widely adopted by industry - evidence of its utility and improvement over previous designs. In their view, this practical success demonstrated both the originality and usefulness required for a valid patent claim under U.S law.