This is a suit for the infringement of P's patent for an improvement in welding and cutting apparatus alleged to have been the invention of one Whitford. The defense is that Whitford was not the first inventor of the thing patented, and the answer gives notice that to prove the invalidity of the patent evidence will be offered that one Clifford invented the thing, his patent being referred to and identified. The application for P's patent was filed on March 4, 1911, and the patent was issued on June 4, 1912. There was no evidence carrying Whitford's invention further back. Clifford's application was filed on January 31, 1911, before Whitford's, and his patent was issued on February 6, 1912. It is not disputed that this application gave a complete and adequate description of the thing patented to Whitford, but it did not claim it. The District Court gave P a decree, holding that, while Clifford might have added this claim to his application, yet as he did not, he was not a prior inventor. The decree was affirmed by the Court of Appeals. D appealed.