The specification is the written description of the invention and of the manner and process of making, constructing, compounding, and using the invention; whatever it may be. He must describe not merely the principle of the invention, but the mode of applying it in such a clear, intelligible manner that those who are "skilled in the art" can, without other aid, use the invention. Nothing should be left to experiment. The phrase "skilled in the art" means persons of ordinary skill. Whether a description is clear, exact and sufficient is a question for the jury whenever it is a matter of legal contention.

In describing an improvement the same rule is applied. The description should show clearly the nature of it. The description should distinguish between the old and the new. "A description in a patent for an improvement is sufficient if a practical mechanic acquainted with the construction of the old machine in which the improvement is made, can, with the aid of the patent and diagram, adopt the improvement." If an inventor intentionally conceals facts or misleads the public by an erroneous description, his patent is void.

Concerning the claim or claims with which the inventor concludes his specification many questions have arisen. First, the claim must be clearly stated so that the public may know what it is. The claim should not be too broad. Several claims may be made, but they should not be varying phraseology for the same thing. They should state the physical structure or elements of mechanism by which the end or result is produced.

The inventor must make oath that he believes himself to be the original and first inventor, that he does not believe that the thing was ever before known or used, and as to his citizenship. If dead or insane, the oath must be made by his executor, administrator, or other representative. After the application is granted another fee of twenty dollars must be paid.

The commissioner of patents must make an examination for the purpose of deciding whether a patent may be granted or allowed. This examination is made by an examiner, whose decision, however, is not conclusive and may be set aside by the commissioner. The patent office is not confined to technical evidence in rejecting applications, but may base its action on anything disclosing the facts relating to the matter.

When objection is made to the form of the application, an amendment may be made by the applicant or his attorney to correct the error; and this may be done at any time prior to the entry by the first examiner of a final order of rejection, and within one year from the date of the preceding action by the patent office.

When two parties apply for a patent for substantially the same thing an interference is declared and the respective parties must present proofs in support of their claims. The question between them is priority of invention. The proceeding then is much like an equity trial with perhaps a wider latitude in admitting evidence bearing on the inquiry.

The applicant, if dissatisfied with the rejection of his claim by the first examiner, or with the decision in an interference case, can appeal to the board of the examiners-in-chief, and if dissatisfied with their decision he may appeal to the commissioner in person, and if still dissatisfied he can appeal to the Court of Appeals of the District of Columbia. All appeals must be taken from the patent office within a year, or a shorter period, if one has been fixed in a decision.

The decision of the commissioner of patents in granting a patent is not conclusive that the inventor is the first and original inventor, but only prima facie, that is, in the absence of other evidence to the contrary. Consequently, the question of patentability in every case may be reexamined in the courts. In the early days of administering the patent law an inventor often applied to a court for an injunction to prevent an infringer from continuing his work. The court, assuming that the patent had been properly granted, did not hesitate, on adequate proof of the infringement to grant the injunction. The courts were not slow in finding out that patents were sometimes granted that ought not to have been, and so the practice was changed and patentees were required to establish their right to a patent in a court of law before a court would enjoin an infringer, except in very clear cases. These hearings in the courts to decide the claims of patentees, are often prolonged, running through years to collect testimony, and are appealed from one court to another finally reaching the supreme federal tribunal. After a patent is thus judicially established injunctions are readily granted against all infringers.

Payment.—In making payment the parties to an agreement always have in mind cash, unless they otherwise agree. Not every kind of money can be used, nor only in limited amounts. Thus, if one owed another a thousand dollars he could not deliver to him, unless he were willing to accept them, one thousand silver dollar pieces, but only ten of them. Nor can a debtor compel his creditor to receive one cent and five cent pieces to a greater amount than twenty-five cents. National bank notes may be paid or tendered to the government, and by one bank to another, yet they may be refused by an individual in payment of his debt. It is important, when one owes another and there is a dispute over the amount, that the debtor should tender or offer to pay his creditor the proper kind of money, because should he offer him some other kind, national bank notes for example instead of United States notes, or those issued by the federal reserve bank, and he declined to take them and should afterwards sue his debtor for the amount, the latter's offer to pay in national bank notes would be regarded as no payment, or even offer of payment.