the Circuit Court for Pennsylvania, the defendant proved that the patented machine had been in use previously to the alleged invention by the plaintiff. The plaintiff then offered to prove that the persons, of whose prior use of the machine the defendant had given testimony, had paid the plaintiff for licenses to use the machine since his patent. This testimony was rejected by the Circuit Court, and the plaintiff thereupon excepted. Marshall C. J. "The testimony offered by the plaintiff was entitled to very little weight, but ought not to have been absolutely rejected. Connected with other testimony, and under some circumstances, even the opinion of a party may be worth something. It is, therefore, in such a case as this, deemed more safe to permit it to go to the jury, subject, as all testimony is, to the animadversion of the court, than entirely to exclude

Whether mere delay of the inventor to take out a patent, without any acquiescence on his part in the public use of his invention in the mean time, or without any use or knowledge of it on the part of public in the mean time, is a good ground of defence, is a question on which the cases do not perfectly agree. It is no objection that the inventor took reasonable time to perfect his invention; but some

56

55 Evans v. Eaton, 3 Wheaton, 454.

See supra, Ch. VII. s. XIX.

cases go much further than this,57 and consider a use for six or seven years by the inventor himself as no forfeiture of his right to a patent, but this doctrine is very questionable, as already suggested.5

A judgment in favor of the patent in a former case for an infringement is not, in a subsequent action for an infringement of the same patent, any estoppel on the defendant against the defence that the patent is void.

Nor is an award of examiners, under the act of 1836, s. 7, in favor of one of the applicants, any estoppel on the other applicant or any other person against contesting the patent.59 But it has been held that the defendant, in an action against him for infringing a patent which he himself had assigned to the plaintiff, is estopped from giving evidence to prove that the invention was not new.60

61

A material defect in the specification is a ground of defence, whether designed or accidental. Mr. Justice Thompson is reported to have stated, in one case, that specifying the whole machine in a patent for an improvement, does not prevent the patent

57 Morris v. Paine's R. 301.

Huntington, 1 Paine's R. 354; Goodyear v. Mathews, 1

58 Infra, Ch. XXIII.

59 Act of 1836, s. 12; and see remarks of Mr. Justice Story, speaking of the similar provision of the act of 1793. Stearns v. Barrett, 1 Mason's R. 174.

60 Oldham v. Longmead, cited 3 T. R. 439, 441.

61 Supra. Ch. XVII. Rese v. Cutler, 1 Stark. R. 354.

from being good for the improvement, though it is not distinguished.62 But the cases seem to be otherwise. The act of congress of 1836, s. 15, in enumerating the defences which may be given under the general issue with notice, does not mention the obscurity or ambiguity, or other defect of the specification through mistake, but the sixth section requires that the specification shall give a description "in full, clear and exact terms," which provision would have no force, if the patentee could recover for an infringement, notwithstanding he had not given such a description, through inadvertency or mistake.

What degree of evidence ought to be required to prove a fraudulent concealment by the patentee in the specification, must rest with the jury to decide. Positive evidence seldom is expected, nor is it necessary. The law requires that such intention should fully appear, but still it may be presumed from circumstances, as if the parts concealed are so essential and so obviously necessary to be disclosed, that no mechanic, skilled in the art, could reasonably be expected to understand the subject, so as from the description given to make the machine, it would be difficult to impute the omission of the patentee to a fair motive.63

62 Goodyear v. Mathews, 1 Paine, 300.

63 Per Washington J. Gray and Osgood v. James and others, 1 Pet. C. C. R. 196, p. 402.

64

Mr. Justice Johnson, at first, entertained the same opinion with other judges of the Supreme Court," that the patent was not defeated by a concealment in the specification made through mistake.65

In a case before Mr. Justice Washington, in 1817, he doubted whether the defendant could, under the general issue, give evidence that the invention was not useful. The ground of his doubt was, that it would be a surprise upon the plaintiff. But no such doubt is intimated in any other case, and it is not apparent that this would be any more a matter of surprise than any other defence that should attack the validity of the patent, and that other defences having that bearing, may be resorted to, is matter of daily practice.67

Mr. Justice Washington remarked, in the case first cited, that this defence that the invention was not useful, came with an ill grace from a defendant who was using it. But it is admissible, and its weight is left to the jury.

68

69

On the question whether mere delay to take out a patent, may invalidate it, Mr. Justice Washington remarks: "It is possible that, without any public

64 Supra, Ch. XI. s. X.

65 Whitney v. Carter, 1807, Fessenden on Pat., Ed. 1822, p. 139. 66 Gray and Osgood v. James and others, 1 Pet. C. C. R. 403.

67 See Langdon v. De Groot, 1 Paine, 203.

68 Gray and Osgood v. James and others, 1 Pet. C. C. R. 403; and see supra, p. 140.

69 Langdon v. De Groot, 1 Paine, 203; Howorth v. Hardcastle, 1 Bing. N. R. 182.

use by others, an unreasonable and causeless, or faulty delay in taking out his patent, might be justly, and upon legal principles, considered as amounting to an abandonment; as to which, however, I avoid giving an opinion."

9970

But, as we have seen, mere delay for the purpose of making an experiment of the invention, will not invalidate the patent," on the defence being urged that the invention had been practised by the inventor, and by another person, before application was made for the patent; Mr. Justice Washington remarked, "If there be any solidity in this argument, the patent law would very nearly become a dead letter, as every inventor uses the machine he invents before he applies for a patent, with a view to satisfy himself whether it answers the purpose for which it was intended."" If any doubts existed on this subject before the act of 1836, that act settles them, since the fifteenth section distinctly recognises the right of the inventor to take sufficient time to adapt and perfect his invention, or in other words, to bring it to bear, before taking out his patent.

70 Treadwell and Watson v. Bladen, 4 Wash. C. C. R. 708. Vide supra, Ch. VII. 8. XIX.

71 Ch. VII. s. XIX.

72 Treadwell and Watson v. Bladen, Wash. C. C. R. 707.