delivered the opinion of the Court:

It must be conceded that the superiority of rolled steel over cast steel for this purpose was well known. Appellant bases his claim for a patent on the ground that, prior to the invention of his apparatus, on which he has obtained a patent, and his process, on 'which an application is pending, it was not regarded as commercially feasible to bend rolled steel rails into circular tracks. It does not even appear in the record before us that, without the aid of appellant’s apparatus and process, it was impossible to accomplish this, but merely that it was commercially impracticable. Therefore we must agree with the tribunals below that whatever invention resides in appellant’s improvements must be confined 10 his apparatus and process. There can be no invention in substituting one known material for another to accomplish a known result. Neither can invention be predicated on the known expedient of making a track of circular formation with a break therein, so that its size may be slightly enlarged or diminished as occasion may require.

Appellant relies chiefly upon the case of Krementz v. S. Cottle Co. 148 U. S. 556, 37 L. ed. 558, 13 Sup. Ct. Rep. 719, *302where a collar button made of a continuous piece of metal, with a hollow shank, was held to be patentable as an article of manufacture. In that case, however, the button was structurally different from anything known to the prior art, while here the particular structure is fully disclosed in the patents cited by the examiner.

The decision of the Commissioner of Patents is affirmed, and the clerk is directed to certify these proceedings, as by law required. Affirmed.