In patent law. this term designates a collision between rights claimed or granted; that is, where a person claims a patent for the whole or any integral part of the ground already covered by an existing patent or by a pending application. Milton v. Kingsley, 7 App. D. C. 540; De- derick v. Fox (C. C.) 56 Fed. 717; Nathan Mfg. Co. v. Craig (C. C.) 49 Fed. 370. Strictly speaking, an "interference" is declared to exist by the patent office whenever it is decided by the properly constituted authority in that bureau that two pending applications (or a patent and a pending application), in their claims or essence, cover the same discovery or invention, so as to render necessary an investigation into the question of priority of invention between the two applications or the application and the patent, as the case may be. Lowrey v. Cowles Electric Smelting, etc., Co. (C. C.) 68 Fed. 372.