Letters patent are granted by the governments of various countries to secure to inventors, their heirs and assigns, for a specified period, the exclusive right to new inventions and discoveries useful to industry. The system was not known to the ancients, and in many countries does not now exist. It is much favored in the United States, is common in Europe and the English colonies, and has been introduced into several South" American countries. In England the authority to grant patents for useful inventions rests upon & proviso in the statute of monopolies passed in 1624. This act prohibited the granting of exclusive privileges in trade, but excepted " letters patent and grants of privilege for the term of one and twenty years or under, heretofore made, of the sole working or making of any manner of new manufacture within this realm, to the first and true inventor or inventors of such manufactures." In France the earliest law in favor of new inventions was passed in 1791. The patent system of the United States has grown up under a positive grant in the federal constitution.

The first act was passed in 1790. The grant of a patent is in the nature of a contract between the government and the inventor, the former giving to the latter the exclusive usufruct of the invention for a limited term in consideration of the benefit received from it by the public. This benefit results from the immediate practice of the invention under the patent, the privilege of practising it after the expiration of the patent, and the general encouragement given to industry. But it is disputed whether patent laws are for the public good. Neither Switzerland nor Holland has such laws. In Prussia the granting of patents is not regarded with favor by the government; and in England, Belgium, Saxony, and some other countries, the abolition of the system has been advocated. - The United States patent office in Washington is a bureau of the interior department; here are kept all records, books, models, drawings, specifications, and other things pertaining to patents. The officers are all paid, and comprise a commissioner, assistant commissioner, and three examiners in chief, appointed by the president with the consent of the senate; also one chief clerk, an examiner in charge of interferences, 24 principal, 24 first assistant, 24 second assistant, and 24 third assistant examiners, a librarian, a machinist, and a large clerical force.

The examiners in chief must be persons of competent legal knowledge and scientific ability. The general law in force relating to patents is that of 1870. - Who may obtain a Patent. Any person, whether citizen or alien, whether resident in this or in a foreign country, being the original and first inventor or discoverer of anything patentable, may obtain letters patent therefor. A patent will issue to the assignee of the inventor, but the application must be made by the latter, and the assignment must be first recorded. In case of the death of the inventor, his legal representatives may apply for the patent. Joint inventors are entitled to a joint patent; but the independent inventors of separate and independent improvements in the same machine cannot obtain a joint patent for their distinct inventions. To be entitled to a patent as the inventor or discoverer, the claimant must be the real author of the invention; and he is the real author who has conceived the essential plan or principle of the discovery. The inventor may, without prejudice to his rights, receive suggestions, hints, or practical aid from others; and he may avail himself of the practical knowledge or manual skill of others necessary to bring his invention into practical form.

Thus Morse conceived the idea of the electric telegraph; and it was held by the supreme court of the United States that the information obtained by him from men of science and mechanicians for the purpose of giving practical embodiment to the conception "neither impairs his rights as an inventor nor detracts from his merits." But if the principle or plan of the invention is substantially communicated to the patentee, who contributes only the ordinary skill of the constructor or mechanic, he will not be regarded in law as the inventor. - What may be patented. Any " art, machine, manufacture, or composition of matter, or any new and useful improvement thereof," may be the subject of a patent. By "art" is meant the mode, process, or manner of doing a thing; the term "manufacture" embraces fabrics or substances, but not machinery; and " composition of matter" is usually applied to medicines, and less frequently to compositions used in the arts, as metallic alloys, paints, chemical compounds, etc. A machine must not be a mere function or abstract mode of operation, separate from any particular mechanism, but a function or mode of operation embodied in mechanism designed to accomplish a certain effect.

If this effect is new, the mechanism which produces it may be new or old; or a new machine which produces an old effect may be patented. The invention may embrace the entire machine, or one or more parts, or it may consist in a combination which may be entirely of old and well known things, or new ones, or old and new together; but the combination must be new, and must produce a new and useful result, not due to the separate actipn of any one of the devices used, but to the cooperative action of all. In this case the patent protects only the combination and the new elements; any one may use the old devices either separately or in a different combination. A patent for an improvement covers only the improvement, and does not give to the patentee a right to use the original invention. The improvement of an existing machine must be real and material, and not merely a change of form. The improvement need not be very great. The difference between the old and the new may to all appearance be very slight, and yet be of great importance.

Thus, when it was the practice to make cloths water-proof by immersing them in a solution of soap and alum, a patent was obtained for immersing cloths first in a solution of alum (with an ingredient or two added), and afterward in a solution of soap; and this patent was sustained, because it was proved that the immersion into the separate solutions successively made the cloth much more completely and permanently water-proof. Since 1842 the law has provided for issuing patents for designs used in manufactures. In England this class of objects is protected by the law of copyright. By the act of congress of 1870 letters patent may be obtained for any new and original design for a manufacture, bust, statue, alto rilievo, or basso rilievo; or for the printing of woollen, silk, cotton, or other fabrics; any new and original impression, ornament, pattern, print, or picture intended for any article of manufacture; or any new, useful, and original shape or configuration of any article of manufacture. For a statement of what is protected by the law of trade marks see Trade Marks. - The essential requisites of every patentable invention or discovery are novelty and utility.

A valid patent will not issue to an applicant if what he claims as new was, before his invention, invented or discovered by another in this country, or if he has abandoned it to the public. Inventors, however, may permit the public use or sale of their inventions for two years before applying for a patent, without prejudicing their rights; but if this use extends over a longer period, or if it amounts to an abandonment, a valid patent will not issue. In regard to a prior invention, it is not sufficient that another may have previously conceived the idea that the thing patented could be done; he must have reduced his idea to practice and embodied it in some useful practical form; it must have been not merely an experiment, but a completed invention or discovery put into practical form and capable of working successfully. Whether it was in actual use is immaterial except so far as that fact may go to determine whether the invention was completed and capable of use. Whoever restores an abandoned or lost art or invention may obtain a patent for it.

If a person having made a discovery or invention applies for a patent in this country, his claim will not be defeated by the fact that the same invention has been previously known and in use in a foreign country, unless it has been patented or fully described in some printed publication. Any inventor or his assignee may obtain a patent for an invention which he has first patented in a foreign country, provided it has not been in public use in the United States for more than two years prior to the application. In this case the patent will expire at the same time as that in the foreign country, or, if there be more than one foreign patent, at the same time with the one having the shortest term; but in no case will it last longer than 17 years. Thus if a patent is granted in this country for an invention previously patented in Prussia for three years, the American patent will not continue beyond that period. - An invention is new, in the sense of the patent law, when it is substantially different from anything previously known. In determining the question of novelty, the inquiry frequently arises whether the supposed invention is really novel, or whether it simply consists in a double or analogous use or application of something already known.

The application of an old contrivance to a new use, or the producing of a new result or effect by known means, is not the subject of a patent if such new use or effect is analogous to that already known. Thus it has been held that a patent will not issue to the person who first applies to railroad cars a kind of wheel that has been-used for other conveyances; nor for a process of curling palm leaf for mattresses after hair had been prepared by the same means. Such uses may be new and useful, but they are analogous to the old, and therefore not patentable. - The discovery of a principle, a natural law, scientific truth, or property of matter cannot in the abstract be the subject of a patent. But whoever makes a new and useful application of any of these things by embodying the principle or law in mechanism, or describing a new process by which the discovery may be made of practical utility, may obtain a patent for his invention, which consists not in the abstract principle but in its practical application.

Thus the properties of electricity, the law of contraction and expansion produced in metals by heat and cold, the principle of centrifugal force, and the qualities of heated air, are well known things which cannot be patented; but their novel application to practical uses by described means have come within the scope of the patent laws. The discovery of ether as an anaesthetic, and its application in surgical operations to alleviate pain, was held to be not patentable, on the ground that the claim was for a new effect " produced by old agents, operating by old means upon old subjects;" it appearing that the existence of ether had been before known, as well as a peculiar effect produced when introduced into the lungs of animals. The principle, law, property, etc, may be newly discovered or well known; and so the mechanism or process or means may be new or old. But it is essential that the practical application to the purpose specified shall be new; that the patentee shall describe some means of applying the principle to a useful purpose; and that the means described shall be such that the practical application may be made by a person of ordinary skill. The law, property, or quality of matter is common property, which can be appropriated by any one to a new purpose by a new adaptation.

No one can acquire exclusive property in the electric fluid, or in any one of its properties or powers; or in the sun's light, or that actinic power by which pictures are painted or impressed. But any one may devise a way of working with electricity, and that way shall be his; and so he may discover a way of making pictures or representations by light, and that way also shall belong to the inventor. And then any other person is at liberty to discover some other way of using either of these forces or qualities of nature. - The statute specifies that the invention shall be "useful;" but any degree of utility is sufficient, and patents are often granted for things of little or no value. The law simply requires that the invention may be capable of some practical use, however trivial, which is not noxious or mischievous. If the invention be new and useful, it is immaterial how much or how little thought, ingenuity, skill, labor, or money has been bestowed upon it. Whether it was the result of repeated experiments and profound study, or was merely an accidental discovery, is immaterial. The law looks to the result, and not to the manner in which it was produced. - Sow Letters Patent may he obtained.

The applicant for a patent is required to file in the patent office a petition on oath or affirmation that the petitioner, if the inventor, believes himself to be the original and first inventor of the invention, and that he does not know and does not believe that it has been known or used before; and this must be accompanied by a full description of the invention, with drawings and a model where the case admits of it. The application must be in writing, addressed to the commissioner of patents, and signed by the inventor if living, or otherwise by his executor or administrator. Even when the application is made by an assignee, it must be signed by the inventor if living. The specification is a written description of the invention or discovery, and of the manner and process of making, constructing, and using it. It must be so full, clear, and exact as to enable any person skilled in the art or science to which it appertains, or with which it is most nearly connected, to make, construct, compound, and use the same. If a machine, the principle and best mode of operation must be fully explained, so as to distinguish it from other inventions.

The description is followed by the "claim," in which the applicant must particularly specify the part, improvement, or combination which he claims as his own invention or discovery. Where there are drawings, the specification must refer by letters and figures to the different parts. In the case of a composition of matter, specimens of the composition and of the ingredients sufficient in quantity for the purpose of experiment, must accompany the application. The chief objects of the specification are to make known the precise nature of the invention, and to enable the public from the specification itself to practise the invention after the expiration of the patent. The object of the claim is to fix with accuracy the extent of what is claimed as new. Two or more separate and independent inventions cannot rightly be claimed in one application; but if they relate to the same subject and are necessarily connected, they may be included in one application. It is essential that the specification he a full and intelligible description of the invention. Obscurity or ambiguity in this respect may defeat the patent. It is also of prime importance that the claim be coextensive with the invention, and discriminate distinctly between the old and what is claimed as new.

If it appear that anything claimed is not new, the patent will be broader than the invention and therefore void. It will also be a fatal defect if the claim is for a machine when the invention is a process; or for the discovery of a law in nature or property of matter, when the invention is the practical application of such law or property. Cases are numerous in which patents have been declared void on account of defective specifications. It sometimes happens that two or more persons claim each to be the first inventor of the same thing. Then the commissioner declares a case of " interference" to exist, and after due notice to the parties, they are heard in support of their several claims before a primary examiner, and if either party is dissatisfied with his decision, before the board of examiners in chief, and if still dissatisfied, before the commissioner on appeal. This may happen although one of the claimants has previously received a patent; for the commissioner, if he comes to the conclusion that the second claimant has a better right, or an equal right, will give him also a patent, and leave the two to determine by legal measures which is valid.

Appeals from the commissioner may be taken in all cases except interferences to the supreme court of the District of Columbia. If a patent is void by reason of a defective specfication, or because the patentee claimed as his own invention more than he had a right to claim as new, he may surrender his patent to the commissioner, and file with him a new and corrected specification, and the commissioner may thereupon issue to him a new patent, provided the error has arisen from inadvertence, accident, or mistake, and without any fraudulent or deceptive intention. Or the patentee may make a disclaimer in writing of such parts of the thing patented as he does not wish to claim; and this disclaimer, being duly received and recorded, shall have the same effect as if it had been originally a part of such specification. Even without such surrender or disclaimer, a patent may still be sustained by the court for any material and distinguishable part for which the claim was valid, although there are other parts of the claim to which the patentee is not entitled; but he can recover no costs for the infringement of such a patent without surrender or disclaimer.

There is a very wise provision to meet the frequent case where an inventor wishes to secure his right, but is not ready to present a full and complete specification, and needs time for experimenting or other purposes. He may file a caveat, which will be placed in the secret archives of the patent office; and if there be any application within a year for anything which appears to interfere with his claim, he shall have notice and may appear and prove priority; and by a second caveat he may renew it for another year, and so on successively. It is to be noticed, however, that a caveat cannot be filed by an alien, unless he has resided in the United States one year, and has made oath of his intention to become a citizen, according to law. Even where caveats are not taken out, all pending applications are regarded as so far confidential that, until after a patent is issued, no information will be given to any one but the claimant respecting the existence of any application, or any questions which may have arisen in relation to it.

To guard against deception of the public as to what inventions are protected by patent, all patented articles are to be marked with the date of the patent, and any person who shall put any word or remark upon a thing not patented which shall indicate that it is the subject of a patent, or put upon it the name of any patentee without his consent, is liable to a penalty of $100 for each offence. A fee of $15 is required on filing the application, and $20 when the patent issues; $10 on filing a caveat, and $30 when application is made for a reissue. The fees for designs are $10 for 3 1/2 years, $15 for 7 years, and $30 for 14 years. - Patents may be assigned by instruments in writing, which must be recorded in the patent office within three months from execution. The assignment may be of the whole or an undivided part of the patent, or a license may be given conferring the exclusive right to make, use, and sell the thing patented within any specified part of the United States. - Term. By the act of 1836 patents were granted for 14 years, and provision was made for an extension in certain cases for 7 years more. In 1861 the original term was fixed at 17 years, and extensions were prohibited for patents granted after that year.

This provision was retained in the act of 1870, so that patents are now issued for 17 years without the privilege of renewal. Patents granted prior to 1861 might formerly be extended by the commissioner after hearing the parties interested, and after public notice to others disposed to object, provided he was satisfied that the patentee, without neglect or fault on his part, had failed to obtain from the use and sale of his invention or discovery a reasonable remuneration. The last patent coming within the provisions of the law in regard to extensions expired March 2, 1875, so that no extension can now be granted except by special act of congress. Such acts have been passed, but the practice is liable to abuses. Patents for designs may be taken out for 3 1/2, 7, or 14 years, as the applicant may elect. - Infringement. To determine what constitutes an infringement is one of the most difficult matters connected with the subject of patents. So much depends upon the points of resemblance and difference between the infringing and infringed matter, that few general rules can be given to determine the question.

The statute affords no definition; it grants to the patentee, for a term not exceeding 17 years, the " exclusive right to make, use, and vend " his invention or discovery throughout the United States. It is therefore an infringement either to make, use, or sell without license what another has patented. In determining the question of infringement, the leading inquiry is whether there is substantial identity between the two things; if so, there is an infringement. If there is a difference, the inquiry is whether it is substantial or merely colorable. When a machine or a process is patented, it is not an infringement to sell the article produced, unless the product is also patented. Thus, where one person owned the patent right for using a machine for making bedsteads in a certain county, it was held to be no infringement for another person operating a similar machine in an adjoining county to sell his bedsteads in the county first named. A combination is not infringed by the use of one or more of its parts, if those parts are not specially patented, and if they do not substantially constitute the combination.

As to infringement by the sale of the thing patented, it must be a sale of the whole thing, and not of the different parts or materials out of which it may be made, unless they be sold with the intent that they should be put together and so make the whole machine. The owner of a patented machine may prolong its existence and utility by repair as long as he can; but he may not construct a new machine under pretence of repairing the old one. A patentee is seldom permitted to call that an infringement which imitates nothing that is directly and explicitly stated in the specification. In case of infringement, the statute provides for the recovery of damages in the circuit courts of the United States. An injunction may also be obtained restraining the alleged offender from further using or selling the patented article. Frequently an injunction will not be granted until the plaintiff's right and the defendant's wrong doing have been established at law. But when the infringement is certain, a court of equity will proceed at once; and sometimes, on .petition of the patentee, they direct a trial at law, and order the defendant to keep an exact account of all that he makes or sells in supposed infringement of the patent, to be rendered if the trial results in establishing the infringement. - The average annual number of applications for American patents is about 20,000. In 1874 there were 21,602 applications, and 13,599 patents were granted, including reissues and those for designs; 2,561 applications were allowed for which patents did not issue on account of non-payment of fees.

The number of caveats filed was 3,181. The receipts of the patent office amounted to $738,278, and the expenditures to $679,288. From 1836 to 1875 more than 158,000 patents were issued. Since 1866 illustrated specifications have been printed by the government; but information concerning patents granted prior to that year is accessible to the public only in manuscript records, the commissioners' annual reports, judicial reports, etc. - Foreign Patent Systems. The English patent system and that of the United States have much in common, but there are some marked differences. The former dates from the reign of James I.; but in 1852 the entire system was regulated by act of parliament. The term " manufactures " in the statute of monopolies has been construed to embrace anything made by the hand of man, including machinery and products, as well as processes or methods of producing manufactured articles, and improvements of the same. In recent statutes the term " inventions " is used, which has the same comprehensive meaning.

Prior to 1852 separate patents were necessary for England, Ireland, and Scotland, and were obtained at a cost of between £300 and £400. One patent is now sufficient for the whole United Kingdom. It may be obtained for 14 years, and at the expiration of that term the owner, by petition to the queen in council, may have an. extension for 7 or even 14 years. The cost of obtaining a patent for 14 years amounts to about £175; but the patentee may secure a term of three years for £25, or seven years for £50 more, to be paid at the end of the first three years. At the expiration of Seven years he may extend the patent for seven years more, by the payment of £100. By filing a provisional specification, the applicant may secure protection for his invention for six months. The commissioners of patents are the lord chancellor and master of the rolls, the law officers of the crown for England, Scotland, and Ireland respectively, and such other persons as the queen may appoint. A marked difference between the English and American system is, that the former gives a patent to any person who first introduces an invention into the realm, without regard to who is the inventor or in what country the invention may have been patented.

The practice therefore has been common, when an invention has been patented or made public in a foreign country, for some other than the owner to send a description to England and obtain a patent for it there. In 1875 a bill was introduced into the house of lords by the lord chancellor to amend the law concerning patents by removing several important defects, one of the most prominent of which was the granting of letters patent without any examination into the merits or novelty of the invention. It was proposed in the new law to issue patents only after examination of the invention; to abolish the practice of granting patents to those who merely introduce inventions from abroad; and to fix the term at 14 years without privilege of extension. The policy of granting patents has been recently much questioned in England. The number of English patents annually issued is between 4,000 and 5,000. Only 68 applications were rejected in 1872, and 78 in 1873. About 70 per cent, of these are allowed to expire at the end of three years, and about 20 per cent, of the remainder cease to exist at the end of seven years.

In 1873 the receipts from patents amounted to £144,760, which exceeded the cost of issue by £90,000. In the United States the number of patents annually issued is much greater than in England, but the surplus receipts are materially less, because the fees required are much smaller, and from 10 to 15 American patents may be required to cover an invention which would be embraced in one English patent. - In France patents are granted for 5, 10, or 15 years, and cannot be extended beyond the last named term except by a special law. The invention must be new and applicable to industry. Pharmaceutical preparations or remedies of any kind cannot be patented; they can only be protected by the law governing trade marks. The application for a patent is made to^the prefecture of the department in which the applicant resides, and embraces a petition to the minister of agriculture and commerce, a specification of the invention or discovery, and the necessary drawings or specimens. The demand must be limited to a single principal object, and the* term desired must be specified. The tax is 500 francs for 5, 1,000 for 10, and 1,500 for 15 years, payable in annual instalments. Letters patent are issued without previous examination, their validity being at the risk of the patentee.

Failure to work the inventions for two years causes forfeiture of the patent. Alterations, improvements, or additions to the invention while the patent is in force may be protected by a certificate, which is obtained by the payment of 20 francs, and expires with the original patent; or a new patent' may be taken out for such improvements. Foreigners may obtain patents upon the same terms as natives. Patents are granted to the authors of inventions already patented abroad; but they expire with the foreign patents. - The imperial constitution of Germany of 1871 declares that questions concerning patents and patent laws are reserved to the Reichstag; but no uniform law for the German empire has yet (1875) been made, and patents are issued by the several states pursuant to their respective laws. The patent system of Prussia has some peculiar features. The invention or discovery must be new and must have industrial value. Inventions of an artistic nature are not patentable. Patents are granted only to natives or to the citizens of such countries as have acquired special rights by treaty, as in the case of British subjects. Foreigners not within this rule may obtain a patent by appointing a Prussian as their representative, in whose name the patent will issue.

Any person, native or foreign, may obtain a patent for an invention patented abroad, provided no description of the invention has been published in Prussia or elsewhere, and that the invention has not been in use in Prussia. As the details of patents granted in England or the United States are promptly published, the English or American inventor who wishes to have his invention patented in Prussia must make contemporaneous application there and at home. The application for a Prussian patent must be made to the minister of commerce in Berlin, and must be accompanied by full descriptions, and also models if necessary. These are kept from the knowledge of all persons except those whose special duty it is to examine and report upon them. All applications are carefully examined by a special department under the ministry of commerce, consisting of nine members under the presidency of a director of the ministry. These decide whether a patent shall issue, and also for what period, which must not be for less than six months nor more than 15 years, but may be for any period within these limits. The usual term for which patents are granted is three years. The cost of obtaining a patent is almost nominal.

The patentee is required to bring his invention into use in Prussia within the time fixed by the minister, which is usually six months and never more than a year; non-compliance with this requirement will render the patent void. The patentee also loses his rights if at any time during the term for which the patent is granted the invention remains unemployed for 12 consecutive months. A Prussian patent gives to the owner the exclusive right of making the article patented, and in the case of machinery the sole right of using it when made; but the patentee cannot prohibit the sale or importation of an article which is like that for which the patent is granted. Infringing articles, in the case of a second offence, are liable to confiscation. The number of Prussian patents annually granted is less than 100; the number of applications is about 700 or 800. In Bavaria patents are granted for any number of years not exceeding 15; the cost ranges from $10 41 for the first to $114 54 for the 15th year. In Saxony the term is five years, but may be prolonged for five more. - In the Austro-Hunga-rian empire the period for which patents are granted is limited to 15 years; but a patent may be taken out for a shorter term at the option of the patentee.

The taxes for 15 years amount to $341: for the first five, $48 72; second five, $97 44; third five, $194 88. The patentee may be a native or a foreigner. The application is made to the political authorities of the district or the provincial governors, and by them forwarded to the ministry of commerce. It must be accompanied by an intelligible description of the invention, and models and drawings if practicable. The description will be kept from the knowledge of the public at the request of the applicant. If the patentee fails to make use of his patent for one year from the date of issue, or subsequently allows two consecutive years to elapse without working his invention, the patent becomes void. A foreign invention can only be patented in case it is patented abroad; and the patent will be granted only to the foreign patentee or his assignee. - In Belgium patents are granted without previous examination, for a term of 20 years. The author of an invention already patented in a foreign country may obtain a patent, which will expire with the foreign patent. The fees are small, and are paid in progressive annual amounts: first year, $1 90; second, $3 80; third, $5 70; and so on to the 20th year, for which the tax is $38. Non-payment of this tax causes forfeiture of the patent.

The proprietor of a patent must use his invention in Belgium within a year from the time it is introduced in a foreign country; if the patented article is used in a foreign country, and not in Belgium, the patent will be annulled unless the owner justifies such non-use. From 1,500 to 2,000 patents are annually granted in Belgium. - In Denmark patents usually run for 3, 4, or 5 years. Important inventions are protected for 10, and in special cases 15 years. Patents are not granted to foreigners for more than 5 years. In Sweden, inventors only, whether Swedes or foreigners, are entitled to letters patent, the term being not less than 3 nor more than 15 years. - In Russia patents are granted for 3, 5, or 10 years. Any person who introduces an invention patented in a foreign country may receive a patent, but it will not continue longer than the foreign patent, and in no case will it last longer than 6 years unless the application is made by the inventor, in which case the term may extend to 10 years. The cost of a patent for 10 years is $357. - In Portugal patents are granted for a term not exceeding 15 years; in Italy not more than 15 years nor less than one year, the tax being annual and proportional. Greece has no patent system; monopoly is obtained only by a special law.

Brazil issues patents for from 5 to 20 years; Venezuela, not more than 15 nor less than 6. - Ourtis's "Law of Patents" (4th ed., 1873) is the standard American work on this subject. The latest English treatise (1874) is by Agnew. The proceedings at the patent office in Washington, with descriptions of all indentions patented, are published weekly in the "Official Gazette," and since the beginning of 1875 all decisions of the United States courts in patent cases. In vol. iv. of that publication (July to December, 1873) may be found statements of the patent laws of various foreign countries.