721, 26 C. C. A. 107. —Contributory infringement. The intentional aiding of one person by another in the unlawful making or selling of a patented invention; usually done by making or selling one part of the patented invention, or one element of the combination, with the intent and purpose of so aiding. Thomson-Houston Electric Co. v. Specialty Co. (C. C.) 72 Fed. 1016;