delivered the opinion of the Court:

The Commissioner of Patents, in passing upon applications, or deciding controversies between rival applicants for patent for the same invention, exercises a power that is essentially judicial. For that reason, Congress has the power to provide for a review of his decisions by appeal to the courts. United States v. Duell, 172 U. S. 576, 43 L. ed. 559, 19 Sup. Ct. Rep. 286. And, in the exercise of that power, an appeal has been given to this court from his order finally rejecting an application for a patent, and from his final orders in interference proceedings.

When the decision of the Commissioner in favor of Lind-mark was reversed by this court and certified to him, he construed it to be a final determination of the controversy between the parties, and, in effect, an award of priority to De Ferranti. The contention of Lindmark that the decision was merely on the merits of his motion for judgment was overruled, and his motion to set a time for taking testimony on other issues in the case and for a final hearing thereon was consequently denied.

Nothing is better settled than that the writ of mandamus cannot be used to perform the office of an appeal or writ of error, or granted in any ease- where there is another adequate remedy. United States v. Duell, 172 U. S. 576, 586, 43 L. ed. 559, 563, 19 Sup. Ct. Rep. 286; Re Key, 189 U. S. 84, 47 L. ed. 720, 23 Sup. Ct. Rep. 624; Ex parte Newman, 14 Wall. 152, 165, 20 L. ed. 877, 879; Seymour v. United States ex rel. South Carolina, 2 App. D. C. 240, 245; Seymour v. United States ex rel. Brodie, 10 App. D. C. 567, 569.

In Ex parte Newman, supra, the circuit court had reversed *603a decree of the district court, sustaining a libel for wages due certain foreign seamen, and dismissed the libel for want of jurisdiction. The amount involved was not sufficient to authorize an appeal to the Supreme Court, and the libellants filed a petition for a mandamus in that court. In an opinion denying the writ, Mr. Justice Clifford said (page 165, 169) : “Applications for a mandamus to a subordinate court are warranted by the principles and usages of law in cases where the subordinate court, having jurisdiction of a case, refuses to hear and decide the controversy, or where such a court, having heard the cause, refuses to render judgment or enter a decree in the case; but the principles and usages of law do not warrant the use of the writ to re-examine a judgment or decree of a subordinate court in any case; nor will the writ be issued to direct what judgment or decree such a court shall render in any pending case, nor will the writ be issued in any case if the party aggrieved may have a remedy by writ of error or appeal, as the only office of the writ, when issued to a subordinate court, is to direct the performance of a ministerial act, or to command the court to act in a case where the court has jurisdiction and refuses to act; but the supervisory court will never prescribe what the decision of the subordinate court shall be, nor will the supervisory court interfere in any way to control the judgment or discretion of the subordinate court in disposing of the controversy. * * * Superior 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 to 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.”

In this case the Commissioner did not refuse to entertain the motion. He gave the party a hearing, and then rendered *604his decision denying the motion. But the interference was not then finally disposed of. No order was entered denying the application of Lindmark, and directing patent to issue to De Ferranti. All that remained to be done by the Commissioner to give effect to the conclusion expressed in his decision on the motion was to render such a final order or decision. Had this been done, Lindmark would have had a right of appeal to this court, in which the action of the Commissioner in the premises could be reviewed. But he did not wait for the entry of the final order, and seeks to review the action of the Commissioner on his motion through this proceeding by mandamus. He should have awaited that order, which has apparently been postponed by this proceeding, and then appealed. Re Connecticut Mut. L. Ins. Co. 131 U. S. clxxx Appx. and 26 L. ed. 561. That case is directly in point. The court below had refused leave to the petitioner to file a petition in a pending suit to compel the master to show cause why he should not be ordered to make a certain deed in accordance with a sale that had been made by him under an order entered in that suit. He applied for a writ of mandamus to compel the execution of the deed. In denying the petition, Chief Justice Waite said: “From the whole case, as presented by the parties, we infer that the court below, as constituted when the application was made, thought the deed ought not to be executed, and it is possible the order now complained of may be the equivalent of a final decree in the cause to that effect, from which an appeal to this court may be taken. But whether that be so or not, we will presume the Court below will not hesitate, on a proper application, to put the record in a shape to enable us to pass on that question in the ordinary course of proceeding to obtain our review. Mandamus can only be resorted to when other remedies fail. It is an extraordinary writ, and should only be used on extraordinary occasions. Here the parties have ample remedy by appeal if they put their case in a condition for such a form of proceeding. As the relator presents his case on this application, he must avail himself of that remedy. We cannot, under the facts he states, expedite the determination of his cause by mandamus.”

*605It has been urged on behalf of the appellant, that the relator had another complete remedy in the case. Having a patent, it is said, he could attack a patent to De Eerranti by virtue of the provisions of sec. 4918, Rev. Stat., H. S. Comp. Stat. 1901, p. 3394. The conclusion reached renders a decision of this point unnecessary, though it may be doubted if this is such an adequate remedy as would prevent relief by mandamus in a case where otherwise the party might show himself entitled to it.

In view of the disposition to be made of this case, it would be improper to express or intimate an opinion in respect of the finality and conclusiveness of the decision of this court in the appeal in the case of De Ferranti v. Lindmark, 30 App. D. C. 417.

It is proper to say, however, that the dismissal of the petition of Lindmark for a construction of the decision as entered in that case was not intended as a determination of the question involved. The time had then elapsed within which a motion for rehearing or to amend the order could be entertained, and the mandate had been issued and delivered to the Commissioner. All that was decided on that petition was, as disclosed in the brief opinion delivered by Mr. Justice Van Orsdel, that “this court * * * has no original jurisdiction to direct and supervise the administration of the affairs of the Patent Office. The allowance of this petition, and the issuance of an order such as prayed for therein, would be an assumption of power such as this court does not possess.” 32 App. D. C. 6.

Eor the reason given, the judgment will he reversed with costs, and the cause remanded with direction to dismiss the petition.

Reversed.