This is an appeal from the Board of Patent Interferences1 which awarded priority to the senior party-appellee on the grounds that the junior party-appellant had suppressed or concealed the invention. 35 U.S.C. § 102(g). We affirm.
FACTS
The invention is an expansible envelope formed from single blanks of folda-*1278ble material. The envelope is open at the top and has a gusset (an inward bellow-type fold forming a triangular insert) on each of the two sides plus one at the bottom, thereby permitting expansion into a box-like configuration.
' It appears that sometime prior to November 4, 1965, appellant conceived the invention which, according to his testimony, would be adaptable to machine folding and gluing of the bottom gusset. Existing three-gusseted envelopes, which were of a different construction from the invention, were only partially manufactured, by machine, the bottom gusset requiring a hand folding and gluing operation. Thus, appellant’s objective was to design a three-gusseted envelope which could be entirely machine-manufactured. Upon receipt by his company of an order for 15,000 three-gusseted filing envelopes from the School District of Philadelphia on November 4, 1965, appellant constructed a model of the envelope. This was introduced into evidence and found by the board to be a completed article, capable of actual use, and further found to have constituted a reduction to practice.
In November, 1965, appellant showed the model to the company vice-president for production and to the plant superintendent, who made a drawing and had a die prepared for the new design. Using the die, paper blanks for the entire order were prepared, and about the last week of November, 1965, were run through one of the company machines. However, the glue did not register in the right positions, the paper blanks were scrapped, new blanks were re-die-cut for hand-fold manufacture, and the order was completed by hand. Nothing further was done with the invention until after August 26, 1966, when an order for 6,000 envelopes was received from the Social District of Philadelphia. Appellant decided to make this run with the new design on another company machine, with new gears and new belts designed to overcome the glue problem encountered in the first run nine months earlier. However, the glue problem was not overcome, and this run (made in September, 1966) was unsuccessful. The paper blanks were thrown away, and again the order was completed by hand, using new blanks for hand-fold manufacture.
No further attempt was made by appellant to produce the invention on the company’s existing machines. However, some eight months later appellant attended an international paper-converting machinery show in Dusseldorf, Germany, for the purpose, as he testified, of looking for a standard folding and gluing machine which would answer the glue problem. Appellant testified that he felt all of the machines that he saw there would handle the problem, but, upon his return, he directed his vice-president for production to get in touch with the International Paper Box Machine Company in New Hampshire, because it was the only company from the United States at the show and would probably provide better service. In the first week of August, 1967, the vice-president visited the International plant in New Hampshire. He made subsequent trips to the plant and ordered a machine on September 13, 1967. The machine was delivered late in December, 1967, assembled, and put into operation in January, 1968. Appellant testified that approximately 25,000 envelopes of the invention design were successfully run off during January.
Meanwhile, on October 31, 1967, some five months after attending the show in Dusseldorf, appellant wrote to his patent lawyer, enclosing samples “to show the style and construction of the expanding envelopes which can be manufactured on the new machine” and saying, “I think we should apply for a patent very soon.” However, no showing was made of when the lawyer was directed to proceed in drawing up the application. It was not until February 7, 1968, following the successful runs on the new machine the month before, that appellant filed his application for a patent.
Under cross-examination appellant testified that he had been in touch with his *1279patent lawyer prior to writing the letter of October 31, 1967, and that “I told him I had invented a new design and that we had experimented with it; we knew that it was a practical design but we were unable to manufacture it with our present equipment.” (Emphasis sup-. plied.)
When asked on cross-examination whether it was his usual practice to delay a period of two years after conception before taking up an invention with his patent solicitor, appellant responded: “I do not apply for a patent until I am positive that we can manufacture the item.”
When asked on cross-examination whether it was correct that his reason for not seeking out the services of his patent solicitor in 1965 was his “doubts” that the envelope could be manufactured at that time, appellant testified: “I had no doubts that it could be manufactured. My doubts were that we could not manufacture it with our present equipment, and the patent itself would be of no value to us unless we could manufacture it.”
Under cross-examination appellant testified, “Oh, yes,” in response to the question: “During the time from November, 1965, to May, 1967, was there a continuous demand for gusseted envelopes?” He also said, “That is correct,” in response to the question: “. . .1 understand that it is much cheaper to make these envelopes by machine than it is by hand; is that correct?”
The board noted that the record shows all of appellee’s activity to have occurred between January 31, 1967, and the date of filing his application for a patent on December 28, 1967, with reduction to practice no later than October 6, 1967, at which time an envelope constructed according to the terms of the count was delivered and explained to his patent lawyer.
There is no evidence in the record to indicate that either party knew of the other party’s activities regarding the present invention until the Declaration of Interference by the Patent Interference Examiner dated June 9, 1969. There is no evidence that appellant disclosed his invention to anyone outside his company, except for a representative of the International Paper Box Machine Company, until it was made known to his patent lawyer in October of 1967.
OPINION
The record before us supports the board’s finding that appellant’s invention was reduced to practice and, further, that this occurred in November, 1965.
The sole remaining question is whether the board correctly held that junior party-appellant suppressed or concealed his invention within the meaning of 35 U.S.C. § 102(g). Here, senior party-appellee bears the burden of proof by a preponderance of the evidence, notwithstanding junior party-appellant’s burden on the issue of priority of invention which he has sustained. Gallagher v. Smith, 206 F.2d 939, 41 CCPA 734 (1953).
In considering the question, we point out that section 102(g) is concerned with the subject of priority of invention and, for interference purposes, provides that a person shall be entitled to a patent unless “before the applicant’s invention thereof the invention was made in this country by another who had not abandoned, suppressed, or concealed it.” By its enactment as part of the Patent Act of 1952, Congress codified the body of law which had accumulated on the subject of priority of invention, including the legal concept of “suppression or concealment.”
We note that commencing with the first edition of Webster’s dictionary in 1828 2 and continuing to the present the definition of “suppress” has included the idea of keeping from public knowledge. It is to be expected, of course, that the courts would be aware of the definition, *1280which fits very well with their statements on the clear policy against suppression underlying our interference laws, both prior to and including 35 U. S.C. § 102(g). Long ago this policy was explained by the U.S. Supreme Court in Kendall v. Winsor, 62 U.S. (21 How.) 322, 328, 16 L.Ed. 165 (1858) as follows:
The true policy and ends of the patent laws enacted under this Government are disclosed in that article of the Constitution, the source of all these laws, viz: “to promote the progress of science and the useful arts,” contemplating and necessarily implying their extension, and increasing adaptation to the uses of society. ... By correct induction from these truths, it follows, that the inventor who designedly, and with the view of applying it indefinitely and exclusively for his own profit, withholds his invention from the public, comes not within the policy or objects of the Constitution or acts of Congress. He does not promote, and, if aided in his design, would impede, the progress of science and the useful arts.
Mason v. Hepburn, 13 App.D.C. 86, 1898 C.D. 510 (1898) has generally been regarded as the origin of the suppression and concealment doctrine. There the court (13 App.D.C. at 96), after quoting from Kendall v. Winsor, emphasized the “policy and spirit of the patent laws” underlying the doctrine as follows:
The true ground of the doctrine, we apprehend, lies in the policy and spirit of the patent laws and in the nature of the equity that arises in favor of him who gives the public the benefit of the knowledge of his invention, who expends his time, labor, and money in discovering, perfecting, and patenting, in perfect good faith, that which he and all others have been led to believe has never been discovered, by reason of the indifference, supineness, or wilful act of one who may, in fact, have discovered it long before.
In Thomson v. Weston, 19 App.D.C. 373, 1902 C.D. 521 (1902), the court reaffirmed its Mason v. Hepburn doctrine —again in reference to “the true policy and ends of the patent laws”:
[B]y deliberate concealment or suppression of the knowledge of his [the inventor’s] invention he subordinates his claim, in accordance with the general policy of the law in the promotion of the public interest, to that of another and bona fide inventor who during the period of inaction and concealment shall have given the benefit of the discovery to the public. Viewed in the light of “the true policy and ends of the patent laws,” the latter is the first to invent, and therefore entitled to the reward.
This court has clearly followed the Mason v. Hepburn doctrine. Brokaw v. Vogel, 429 F.2d 476, 57 CCPA 1296 (1970); Woofter v. Carlson, 367 F.2d 436, 54 CCPA 917 (1966). It has, to be sure, cautioned that the doctrine is to be applied only where the record sustains the burden of proving suppression or concealment. Frey v. Wagner, 87 F.2d 212, 24 CCPA 823 (1937); Woofter v. Carlson, supra. At the same time, the court has declared that application of the Mason v. Hepburn doctrine is not to be confined to “extreme cases” and that it—
. is a very healthy rule to be invoked in the public interest whenever the fact situation warrants it. While the law may abhor a forfeiture, the Mason v. Hepburn principle is not a forfeiture in the true sense; rather, it is a rule according to which the patent right goes to the most deserving.
Brokaw v. Vogel, supra. Needless to say, evidence of one party’s being “first to file” would hardly satisfy his burden of proving suppression by the other party.
As we have done before, we emphasize here that each case involving the issue of suppression or concealment must be considered on its own particular set of facts. Myers v. Feigelman, 455 *1281F.2d 596, 59 CCPA 834 (1972); Engel-hardt v. Judd, 369 F.2d 408, 54 CCPA 865 (1966). In such consideration, two guideposts have been firmly established:
First, the length of time from reduction to practice to filing of an application for a patent is not determinative. Woofter v. Carlson, supra; Schnick v. Fenn, 277 F.2d 935, 47 CCPA 1174 (1960). Mere delay, without more, is not sufficient to establish suppression or concealment. Gallagher v. Smith, supra. However, the warning has been sounded that one who delays filing his application does so at the peril of a finding of suppression or concealment due to the circumstances surrounding the delay. Woofter v. Carlson, supra. See also Watson, Commissioner of Patents v. Allen, 103 U.S.App.D.C. 5, 254 F.2d 342 (1958); International Glass Co., Inc. v. United States, 408 F.2d 395, 187 Ct.Cl. 376 (1968).3
Second, spurring into filing an application for a patent by knowledge of another’s entry into the field (e. g. by issuance of a patent) is not essential to a finding of suppression or concealment. Dewey v. Lawton, 347 F.2d 629, 52 CCPA 1573 (1965); Brokaw v. Vogel, supra; Gallagher v. Smith, supra.
Bearing these points in mind, we now turn to the question of appellant’s intent to suppress. This, if established by the evidence of record, coupled with the delay in filing his application for patent, would support the board’s finding of “suppression” for purposes of 35 U.S.C. § 102(g). The facts show a delay from reduction to practice in November of 1965 until February 7, 1968, when appellant’s application for a patent was filed. During this period there was a “continuous demand” for gusseted envelopes which, if machine-produced, would cost less.
The delay was not for the purpose of perfecting appellant’s invention — a critical point of distinction from other cases holding that delay was justifiable and, therefore, suppression or concealment had not been proved. Frey v. Wagner, supra (“The law does not punish an inventor for attempting to perfect his process before he gives it to the public. . reasonable experimentation is frequently encouraged.”); Altorfer v. Haag, 74 F.2d 129, 22 CCPA 806 (1934) (following reduction to practice, frequent and comparative tests of machines equipped with the invention with a view to determining best materials for manufacture of invention and refinements that should be made); Dewey v. Lawton, supra (testing and refinement of invention for more than a year after reduction to practice); Schnick v. Fenn, supra (“mitigating circumstances” included continuing development, after reduction to practice, of best design and tests in further perfecting the invention) ; Watson, Commissioner of Patents v. Allen, supra.
Instead, the evidence discloses that the delay here resulted from appellant’s intent to wait, without disclosing his invention — not to perfect the invention, but: first, to determine whether the invention could be produced with his company’s own equipment; then, when that could not be done (after two attempts nine months apart), some eight months later to locate a machine which would enable his company to manufacture it; and, finally, some eight months after that, to have a successful run on the new machine. Appellant argues that a “generalized search” went on for a machine to produce his envelope. However, this is based on mere hearsay testimony of the supervisor of appellant’s plant, as follows:
Q. What was being done in the office then?
*1282A. They were trying to find better equipment.
Q. Were any of their efforts brought to your attention?
A. No.
Q. How did you know they were trying to find better equipment?
A. Because they did. When I say they were not brought to my attention nobody said “We are going out to look at this and this machine,” but there was discussion about trying to find a machine but the actual discoveries or failures were not discussed with me.
Aside from appellant’s trip to the Dusseldorf show over a year and a half after reduction to practice and the follow-on visits to the International plant in New Hampshire by the company’s vice-president, the record is devoid of any meaningful evidence to support appellant’s “generalized search” argument. Rather, it supports a finding of total inactivity. For example, appellant has made no showing that an equipment catalog was consulted or that even one telephone call or letter of inquiry was made to a machine manufacturer prior to his trip to Dusseldorf where, interestingly, he located a machine produced by a U.S. manufacturer. Considering the two unsuccessful runs on the machines of appellant’s company, we believe some such evidence should have been forthcoming to establish ordinary- business prudence on the part of appellant in locating a suitable machine during the over a year and a half period following reduction to practice.
In his own words, appellant’s excuse for the delay in filing his application was simply: “I do not apply for a patent until I am positive we can manufacture it.” And, indeed, appellant delayed filing his application until after the successful fun, when he was positive that the invention could be produced on his company’s new machine. Unlike Schnick v. Fenn, supra, where early in the delay period the inventor had his patent attorney make a preliminary search for which his company was billed, appellant delayed some twenty months after reduction to practice before furnishing his patent lawyer samples of his invention. This was five months after the Dusseldorf show where, appellant testified, he thought all the machines he saw would satisfy his problem. Even then, appellant merely told his patent lawyer that he thought “we should apply for a patent very soon.” And it was not until over three months later, after the successful runs on the new machine, that appellant filed his application.
Meanwhile, as found by the board, ap-pellee, without knowledge of appellant’s activities, conceived and reduced his invention to practice between January 31, 1967, and October 6, 1967, at which time he delivered and explained to his patent lawyer an envelope constructed according to the count. Less than three months later, he filed his patent application. Also, the record shows that in early March, 1967, appellee sent samples of blanks for envelopes to the International plant in New Hampshire to be run on an experimental machine (which was built for exhibition at the Dusseldorf show later in the year). Appellee made a downpayment for one of the machines by check dated May 1, 1967, and the machine was delivered in late July or early August, 1967. We believe the nature and tempo of appellee’s activities were in accord with ordinary business prudence.
In view of the foregoing and considering the record as a whole, we hold that junior party-appellant suppressed his invention within the meaning of 35 U.S.C. § 102(g).
The decision of the board is affirmed.
Affirmed.
. Interference No. 96,865 between Young on his application No. 703,663, filed February 7, 1968, and Dworkin on his application No. 694,141, filed December 28, 1967.
. An American Dictionary of the English Language, S. Converse, New York, 1828.
. Thus, when the delay period is determined to be “unreasonable,” there is a basis for inferring an intent to suppress. Brokaw v. Vogel, supra. The activities of an inventor during the delay period (e.g. steps to improve or perfect the invention after it has been reduced to practice) may well excuse the delay and, thereby, support a finding that it was “reasonable.” Frey v. Wagner, supra.