=Patents.=--A patent is a form of protection granted by the government to an inventor to secure to him for a limited period the exclusive enjoyment of the fruits of his skill and industry. Patents were granted by the state governments until the Constitution conferred this power on Congress. In 1790 Congress passed a law authorizing the granting of patents for new and useful inventions, and this law has been amended and its scope extended several times since. _The Patent Office._--In 1836, an office or bureau charged with receiving applications, conducting examinations, and granting patents was created in the department of state, but it was transferred to the department of the interior in 1849. This office has grown to be one of the largest and most important branches of the government service. It has a large number of examiners and experts arranged in groups, each of which examines the applications for patents for inventions of a particular class. _Conditions._--The applicant for a patent must declare upon oath that he believes himself to be the original inventor of the article for which he desires a patent, and he must submit with his application a full description or drawing of the invention, and if demanded, also a model of the same. The invention must be a useful one, for patents will not be granted for inventions which have no practical or scientific value. If the patent is refused by the commissioner of patents, the applicant can take an appeal to the court of appeals of the District of Columbia. A fee of fifteen dollars is charged for filing the application, and one of twenty dollars for issuing the patent.[49] The term for which a patent may be issued under the present law is seventeen years, which term may be extended only by act of Congress. When a patent is granted the word "patented" with the date on which it was issued must be placed on the article in order that the public may have notice of the fact that it is patented. During the term of the patent the inventor has the exclusive right to manufacture, use, or sell the article, and in case of infringement the law allows him to apply for an injunction to restrain the infringer, or to sue for damages. Patents, like copyrights, may be assigned or otherwise transferred, provided a record of the transfer is made in the patent office.[50] [49] Notwithstanding the large number of employees in the patent office, the office is self-supporting by reason of the fees charged and the large number of applications, the annual receipts amounting to more than $2,000,000. [50] An inventor who needs more time in which to perfect his invention and to forestall the action of some one else may secure a caveat which gives him a year in which to complete his invention. Trade-marks are also registered by the patent office provided they are to be used in interstate commerce. Trade-marks in other cases are usually protected by state registration.