delivered the opinion of the Court:
Appellants concede what has many times been ruled by this court, that an award of priority does not necessarily entitle the party in whose favor the award is made to a patent. Sobey v. Holsclaw, 28 App. D. C. 65; Burson v. Vogel, 29 App. D. C. 388; Gueniffet v. Wictorsohn, 30 App. D. C. 432; Norling v. Hayes, 37 App. D. C. 169. The jurisdiction of the Commissioner in the premises, therefore, is not questioned. The ground of attack is the manner of the exercise of that jurisdiction. In other words, the real contention of appéllants is that if the Commissioner is permitted to proceed in the manner indicated, he will commit error. It is apparent at once that appellants overlook the fact that mandamus cannot be made to perform the function of an appeal or writ of error, and that it ordinarily will not be granted if there is another legal remedy, nor unless the duty sought to be enforced is clear and indisputable. United States v. Duell, 172 U. S. 576, 43 L. ed. 559, 19 Sup. Ct. Rep. 286; Moore v. United States, 40 App. D. C. 591. In Ex parte Newman, 14 Wall. 152, 20 L. ed. 877, the court said: “Superi- or tribunals may by mandamus command an inferior court to perform a legal duty where there is no other remedy, and the rule applies to judicial as well as ministerial acts, but it does not apply at all to a judicial act to correct an error, as where the act has been erroneously performed. If the duty is unperformed, and it be judicial in its character, the mandate will be to the judge directing him to exercise his judicial discretion or judgment, without any direction as to the manner in which it shall be done; or if it be ministerial, the mandamus will direct the specific act to be performed.” Thus, in United States ex rel. Steinmetz v. Allen, 192 U. S. 543, 48 L. ed. 555, 24 Sup. Ct. Rep. 416, relied upon by appellants, the Primary Examiner had declined to forward an appeal prayed by the petitioner to the Board of Examiners in Chief to review the ruling of the Examinér requiring petitioner to cancel certain of his claims. *179It appearing that the only way the petitioner could receive adequate protection was by compelling the Examiner to forward the appeal as the law required, mandamus was allowed. The court pointed out that if the petitioner had yielded to the rule requiring the cancelation of certain of his claims, he necessarily would have given up his right to join those claims in one application, and that if he had not yielded to the rule, he could not have been heard at all; and that a ruling having such an effect was to be considered as final and appealable. There was therefore a plain duty which the Patent Office refused to perform.
In the instant case it is conceded that a right of appeal will lie to this court to correct any error that may be committed by the Commissioner in the determination of the question before him. The Commissioner having jurisdiction, and a plain and adequate remedy by appeal being open to appellants, we are not at liberty to determine in advance, through mandamus proceedings, in what manner the Commissioner shall exercise his jurisdiction. Billings v. Field, 36 App. D. C. 16. It well may be that a defeated party in an interference proceeding ought not to be permitted, except in a very unusual and plain case, to assume such an inconsistent position as the protestant in the present case’ has apparently assumed, and by so doing, prolong the litigation and add to the already heavy burdens of the party in whose favor the award of priority has been made. But that is a question for the Commissioner, and not for this court.
The decree will be affirmed, with costs. Affirmed.