delivered the opinion of the Court:

John A. Heany, as the sole inventor, is the applicant for the patent in each case pending in the Patent Office, and, whether he has assigned his interests in the inventions or not, the applications must be prosecuted in his name. Whether his assignees are proper parties as complainants' in this bill is a question that was not presented in the court below, and will not therefore, be considered as involved here.

The injunction granted not only restrains the Commissioner of Patents from taking any action affecting the applications of Heany, but also prohibits him from prosecuting the investigation of the charge of corrupt practices in his office relating thereto.

The Commissioner of Patents is the official head and ad*37ministrator of a great and important public office. The duties devolved upon him are both executive and judicial in their character. As an executive officer it is his duty to see that the business of the office is carried on honestly, methodically, and with reasonable despatch. As regards every application for a patent, there are two interests involved,—that of the applicant and that of the public. It is the duty of the Commissioner to see that the formal requirements of the statutes relating to applications are complied with. "When an application is found to be sufficient in form, it then becomes his duty to inquire and determine if the applicant is justly entitled to the patent as claimed. The investigation of the claim involves the adjudication of disputed questions of fact, upon scientific or legal principles. The proceeding is essentially judicial in its character.

As a necessary incident of these general powers, the Commissioner has the power to institute investigations into the conduct of his office generally with a view to the efficiency of the service and the eradication of corrupt practices, if such are found to exist.

In what manner such investigations shall be conducted and testimony elicited is a matter within the discretion of the Commissioner, and no court is vested with supervisory power over him. To the extent, then, that the injunction restrains any inquiry into the charges of improper practices in relation to the pending applications, it is clearly erroneous. Whenever, as the result of such an investigation, the Commissioner undertakes action that would injuriously affect an applicant’s right of property, or tend to deprive him thereof, he must act by authority of, and according to due process of, law.

In so far, however, as the proposed investigation of the charges of fraudulent alterations of Heany’s applications might incidentally affect his interests, due process of law seems to have been pursued. Copies of the charges were delivered to him, and notice was given also that testimony would be taken with an opportunity to hear and cross-examine the witnesses to be introduced, as well as to offer any testimony in opposi*38tion. Just and careful regard was had for the incidental rights and interests of Heany in these preliminary steps.

It does not follow from proceedings so begun, that- the charges would necessarily be sustained, and, moreover-, that the Commissioner púrposed to destroy inchoate rights of the applicant in such manner that he would be deprived of a right to appeal from this final order in the premises.

The injunction not only went farther than there is any warrant for, as above intimated, but, in so far as it seeks to protect the ultimate rights of the applicant, it is, at least, premature. °

But, assuming, as has been contended, that the avowed purpose of the proposed investigation was to' furnish a foundation for striking the applications from the files, and that such would be its probable result, has the equity court the power to restrain the Commissioner?

The power to enjoin the action of an executive officer, or of a subordinate tribunal, in a given case, rests upon the same foundation as that to compel action by mandamus. As has been recently held in an analogous case, the writ of' mandamus cannot be used to perform the office of an appeal or writ of error; nor will it lie where there is another plain and adequate remedy for the injury done. Moore v. United States ex rel. Lindmark, 33 App. D. C. 597 (present term).

It is not necessary to determine whether rule 31 of the Patent Office, under which the Commissioner claims the power to strike from the files an application that has been fraudulently altered, is, in its entire scope, consistent with the statutes governing procedure in the Office. The question is a difficult one, and it may be conceded that it is doubtful if it is so to the full extent of the scope claimed for it. Clearly, however, the Commissioner has the power, either in an ex parte or an interference case, to inquire and determine whether an application has been altered or substituted without authority. Whether such an alteration shall have been made by the attorney of the applicant, with the latter’s connivance or consent, is immaterial. The efficacy of the application would be *39destroyed by such alteration. It would no longer be tbe application contemplated by the statute as the foundation of the patent.- • Nor is the power to so declare, as the result of investigation, barred by the adjudication in the criminal case. The question adjudicated therein was not whether the application had been altered, but whether the applicant was a guilty party thereto. The fact of alteration is not res judicata.

It is conceded that if, instead of striking the application from the files on account of an alteration or unauthorized amendment, the Commissioner should reject it formally, an appeal would lie to this court from the order of rejection. But if, instead of a formal rejection, the Commissioner should order the application stricken from the files, it seems to the writer that an appeal would also lie from that order.

A court would look to the substance, the necessary effect and operation of the order, rather than to its formal recital merely. Surely the Commissioner may not, by striking an application from the files, when regularity required its rejection for the same cause, take away an applicant’s right of appeal. No matter what the form of the order, the effect is substantially the same; namely, the final refusal of a patent to which the'party might justly be entitled. We do not decide this point,, however, as our decision may be rested upon another and more satisfactory ground.

We cannot entertain a presumption that the Commissioner has predetermined the action to be taken as a result of his investigation. We must presume that, if he finds the alterations to have been made, but-without, the knowledge and consent of the applicant, he will permit it to be corrected so as to restore it to its condition as originally filed. In that event there will be nothing of which the applicant can complain.

If, on the other hand, he finds that it was tampered with by th»'-eonnivance and approval of the applicant, he will probably enter an order rejecting the application, leaving the applicant his right to appeal therefrom. We cannot presume that he will not. Should he strike the application from the files, and it should transpire that no appeal could be prosecuted from *40that order, the applicant might then proceed by mandamus to compel him to vacate that order and give the applicant a hearing on his right to have his application entertained. No such irreparable injury could- result, under the conditions suggested, as would warrant the interposition of a court of equity.

The courts are invested with no power to interfere with or to supervise the practice of the Patent Office. It is only in cases where a hearing is refused a party, or the Commissioner refuses to perform a plain duty, or where he undertakes to do an unwarranted act, for which there is no other adequate remedy, that the courts are authorized to interfere by mandamus or injunction.

No such case is presented on this record. The decree for the injunction will be reversed, with costs, and the cause remanded with direction to dismiss the bill. Reversed.

On the 15th day of November, 1909, the Court, by Mr. Chief Justice Shepakd, handed down the following additional opinion:

These two appeals, one special and the other general, from the same order, were considered together without question raised as to the sufficiency of either appeal. The decree entered should have disposed of both, and it is now amended so as to apply to each.

Application has been made by the appellees for an appeal from the decree entered here to the Supreme Court of the United States. We are of the opinion that no appeal lies in such a case. Durham v. Seymour, 161 U. S. 235, 40 L. ed. 682, 16 Sup. Ct. Rep. 452. The application for allowance of the appeal is therefore denied.

On November 27, 1909, on application by the appellees to one of the justices of the Supreme Court of the United States, an appeal to that court was allowed.