delivered the opinion of the Court:

Appellant contends that the device disclosed by appellee in ■1904 was inoperative, in that the main source of current is a *580machine having a rising, instead of a drooping, characteristic, and can therefore avail him nothing. All of the tribunals below, however, held that the invention disclosed was identical with that described in the application and patent. No motion to •dissolve the interference was made by appellant, but the Examiner of Interferences of his own motion considered the question of the inoperativeness of the device described in appellee’s patent, and decided in favor of appellant. On appeal to the Board of Examiners-in-Chief this decision was unanimously reversed, the board being affirmed on appeal to the Commissioner. This invention involves an extremely technical science, and, at most, error is not so apparent as to warrant us in overturning not only the decisions of the two appellate tribunals of the Pat •ent Office, but also the decision of the Primary Examiner, one skilled in the particular art to which this invention relates, who must have considered appellee’s application to disclose an ■operative device, since he allowed it to go to patent.

It is also contended by counsel for appellant that the testimony on behalf of appellee shows that he was but the inventor ■of an unimportant portion of the invention, and that some undisclosed third party was the true inventor of the remainder. It is unnecessary here to determine whether or not appellant is in a position to raise this question. The Examiner of Interferences and the Commissioner both held the evidence proved conception on the part of appellee of the whole apparatus embraced in the issue, and the Board of Examiners-in-Chief evidently did not regard the question as of sufficient importance to consider it. An examination of the record convinces us that appellee’s testimony establishes a prima facie case, which is •sufficient, in the absence of any direct proof to the contrary, ■or any claim advanced by such third person.

It is further contended by counsel for appellant that appellee had abandoned his invention, and was only spurred to activity when he learned of appellant’s entry into the field. Appellee was undoubtedly lacking in diligence, but this is not chargeable against him, since he was the first to conceive and the first to reduce to practice. We agree with the Commissioner that the facts *581do not show an intention to abandon the invention. Appellee turned the matter over to the patent department of the General Electric Company, by which he was employed, and to which he had assigned his patent rights. While it is true that he-states the matter dropped out of his mind, yet he explains-this in the same sentence by the statement that he “knew the-patent department would look after their patent situations.”' Abandonment must be strictly proved, and will never be presumed. The burden of. proof is on appellant. A mere delay in the filing of an application of less than three years will not alone amount to abandonment. There seems to have been no-attempt at concealment, since the invention was disclosed not only to engineers in the employ of the General Electric Company, but also to others not connected with it.

Ordinarily, the one who is the first to conceive and the first to reduce to practice is regarded as the true inventor. An exception, however,’ has been made in the case of Mason v. Hepburn, 13 App. D. C. 86, relied upon by appellant, where one, although the first to conceive and reduce to practice, by concealing and suppressing his invention, was held to have abandoned it, and to be subordinated to the rights of one who-entered the field in good faith as an independent inventor, and was the first to give the completed invention to the world. It is the spirit and intent of the patent laws to reward the one who first gives the public the benefit of his invention in its completed form, and this will be done unless the one first to-conceive, but the last to reduce to practice, is not chargeable with delay. But in this case appellant was not the first to-give the invention to the world. Ilis application for patent was not filed until nearly a year and a half after appellee’s. Had appellant reduced to practice before appellee, there could be no question of his right to a patent, since appellee was not exercising diligence at the time his rival entered the field. On the other hand, had appellee made his application without, knowledge of appellant’s efforts, he would undoubtedly be entitled to prevail, since he was the first to conceive and the first to reduce to practice, and his want of diligence would become immateri al.

*582But appellant contends that, where one is only spurred to •activity by knowledge of the entry of another into the field, his rights become subordinated to those of the later inventor, ■even though the latter was not the first to reduce to practice. To sustain this contention, it would be necessary to hold that the rights of the earlier inventor become absolutely forfeited at the date he receives knowledge of the other’s subsequent conception, without regard to the diligence of the latter. Thus, •one, because of his delay, would be totally deprived of his right' to a patent for his invention-—-the incentive offered by the patent laws to induce him to perfect and disclose it—at a time when there is no assurance that his rival would have a .greater regard for the interests of the public. The purpose of the patent laws is to secure to the people at large, in return ■for a limited monopoly, the fruits of inventive genius, without unreasonable delay. “The interests of the public are therefore the primary consideration, and to these the privileges .granted to inventors are secondary and subordinate. * * * On this principle the inventor is required to be diligent in reducing his conception or invention to practice; and it is usually the first who reduces to practice, and not the first who ■conceives, that is entitled in law to be regarded as the inventor.” Warner v. Smith, 13 App. D. C. 111.

To hold that the earlier inventor’s right is merely suspended, to be revived again in case the later is also guilty of laches, is equivalent to a ruling that one is restricted to the date, as his date of conception, when, after delay, he re-enters the field .and begins to perfect his invention, and that, from that time, it is a race of diligence between the two. This contention was urged in the case of Grabowsky v. Gallaher, 39 App. D. C. 548, but was denied upon the authority of the case of Paul v. -Johnson, 23 App. D. C. 187. In the latter case, Paul was the first to conceive, but the last to reduce to practice, being ■chargeable with negligence. Johnson conceived before Paul ■re-entered the field, but was also guilty of lack of diligence until after that time. The court said: “It is urged on behalf of Paul, that even though he were lacking in diligence up to *583February 28, 1896, the time when he communicated- with and placed the matter of his claim to invention in the hands of his counsel, he should, nevertheless, prevail because of the alleged lack of diligence on the part of Johnson, and from which time Paul had become active. But this contention, if sustained, would contravene a well-settled principle of patent law. As well said by the Commissioner in his opinion, it is a fundamental principle of patent law that the first to reduce to practice is prima facie the first inventor and entitled to a patent. Prior to the act of July 4, 1836, his right was absolute and subject to no exception. It has been repeatedly held by the Supreme Court of the United States, that he is to be regarded as the inventor and entitled to the patent who first brought the machine to perfection and made it capable of useful operation. The first and only exception made to this established rule was that made by the act of Congress of July 4, 1836, now embodied in sec. 4920, Revised Statutes of the United States, U. S. Comp. Stat. 1901, p. 3394, wherein it is provided that anyone sued for infringement of a patent may show ‘that he [the plaintiff] had surreptitiously or unjustly obtained the patent for that which was in fact invented by another, who was using reasonable diligence in adapting and perfecting the same.’ Nothing is said as to diligence on the part of the first to reduce to practice, and no lack of diligence can be imputed to him, since he was in fact the first to give the invention to the public by a reduction to practice. The principle is well and clearly stated by Judge Taft, in delivering the opinion of the circuit court of appeals of the sixth circuit in the case of Christie v. Seybold, 5 C. C. A. 33, 6 U. S. App. 520, 55 Fed. 69. In that case the judge said: ‘The diligence of the first reducer to practice is necessarily immaterial. It is not a race of diligence between the two inventors in the sense that the right to the patent is to be determined by comparing the diligence of the two, because the first reducer to practice, no matter what his diligence or want of it, is prior in right, unless the first conceiver was using reasonable diligence at the time of the second conception and the first reduction to practice.’ ” Appel*584lant was neither the first to conceive nor the first to reduce to practice.

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

A motion for a rehearing was overruled October 8, 1913.