A steam engine is a heat engine that performs mechanical work using steam as its working fluid. The steam engine uses the force produced by steam pressure to push a piston back and forth inside a cylinder; this pushing force is transformed, into rotational force for work. The term "steam engine" is applied only to reciprocating engines as just described, not to the steam turbine. Steam engines are external combustion engines, where the working fluid is separated from the combustion products; the ideal thermodynamic cycle used to analyze this process is called the Rankine cycle. In general usage, the term steam engine can refer to either complete steam plants such as railway steam locomotives and portable engines, or may refer to the piston or turbine machinery alone, as in the beam engine and stationary steam engine. Steam-driven devices were known as early as the aeliopile in the first century AD, with a few other uses recorded in the 16th and 17th century. Thomas Savery's dewatering pump used steam pressure operating directly on water.
The first commercially-successful engine that could transmit continuous power to a machine was developed in 1712 by Thomas Newcomen. James Watt made a critical improvement by removing spent steam to a separate vessel for condensation improving the amount of work obtained per unit of fuel consumed. By the 19th century, stationary steam engines powered the factories of the Industrial Revolution. Steam engines replaced sail for ships, steam locomotives operated on the railways. Reciprocating piston type steam engines were the dominant source of power until the early 20th century, when advances in the design of electric motors and internal combustion engines resulted in the replacement of reciprocating steam engines in commercial usage. Steam turbines replaced reciprocating engines in power generation, due to lower cost, higher operating speed, higher efficiency; the first recorded rudimentary steam-powered "engine" was the aeolipile described by Hero of Alexandria, a mathematician and engineer in Roman Egypt in the first century AD.
In the following centuries, the few steam-powered "engines" known were, like the aeolipile experimental devices used by inventors to demonstrate the properties of steam. A rudimentary steam turbine device was described by Taqi al-Din in Ottoman Egypt in 1551 and by Giovanni Branca in Italy in 1629. Jerónimo de Ayanz y Beaumont received patents in 1606 for 50 steam powered inventions, including a water pump for draining inundated mines. Denis Papin, a Huguenot refugee, did some useful work on the steam digester in 1679, first used a piston to raise weights in 1690; the first commercial steam-powered device was a water pump, developed in 1698 by Thomas Savery. It used condensing steam to create a vacuum which raised water from below and used steam pressure to raise it higher. Small engines were effective, they were prone to boiler explosions. Savery's engine was used in mines, pumping stations and supplying water to water wheels that powered textile machinery. Savery engine was of low cost. Bento de Moura Portugal introduced an improvement of Savery's construction "to render it capable of working itself", as described by John Smeaton in the Philosophical Transactions published in 1751.
It continued to be manufactured until the late 18th century. One engine was still known to be operating in 1820; the first commercially-successful engine that could transmit continuous power to a machine, was the atmospheric engine, invented by Thomas Newcomen around 1712. It improved on Savery's steam pump. Newcomen's engine was inefficient, used for pumping water, it worked by creating a partial vacuum by condensing steam under a piston within a cylinder. It was employed for draining mine workings at depths hitherto impossible, for providing reusable water for driving waterwheels at factories sited away from a suitable "head". Water that passed over the wheel was pumped up into a storage reservoir above the wheel. In 1720 Jacob Leupold described a two-cylinder high-pressure steam engine; the invention was published in his major work "Theatri Machinarum Hydraulicarum". The engine used two heavy pistons to provide motion to a water pump; each piston was returned to its original position by gravity.
The two pistons shared a common four way rotary valve connected directly to a steam boiler. The next major step occurred when James Watt developed an improved version of Newcomen's engine, with a separate condenser. Boulton and Watt's early engines used half as much coal as John Smeaton's improved version of Newcomen's. Newcomen's and Watt's early engines were "atmospheric", they were powered by air pressure pushing a piston into the partial vacuum generated by condensing steam, instead of the pressure of expanding steam. The engine cylinders had to be large because the only usable force acting on them was atmospheric pressure. Watt developed his engine further, modifying it to provide a rotary motion suitable for driving machinery; this enabled factories to be sited away from rivers, accelerated the pace of the Industrial Revolution. The meaning of high pressure, together with an actual value above ambient, depends on the era in which the term was used. For early use of the term Van Reimsdijk refers to steam being at a sufficiently high pressure that it could be exhausted to atmosphere without reliance on a vacuum to enable it to perform useful work.
Ewing states that Watt's condensing engines were known, at the time, as low pressure compared to high pressure, non-condensing engines of the same period. Watt's patent prevented others from making high pres
Newburyport is a small coastal and historic city in Essex County, United States, 35 miles northeast of Boston. The population was 17,416 at the 2010 census. A historic seaport with a vibrant tourism industry, Newburyport includes part of Plum Island; the mooring, winter storage and maintenance of recreational boats and sail, still contribute a large part of the city's income. A Coast Guard station oversees boating activity in the sometimes dangerous tidal currents of the Merrimack River. At the edge of the Newbury Marshes, delineating Newburyport to the south, an industrial park provides a wide range of jobs. Newburyport is on a major north-south highway, Interstate 95; the outer circumferential highway of Boston, Interstate 495, passes nearby in Amesbury. The Newburyport Turnpike still traverses Newburyport on its way north; the Newburyport/Rockport MBTA commuter rail from Boston's North Station terminates in Newburyport. The earlier Boston and Maine Railroad leading farther north was discontinued, but a portion of it has been converted into a recreation trail.
Newburyport was settled in 1635 as part of Newberry Plantation, now Newbury. On January 28, 1764, the General Court of Massachusetts passed "An act for erecting part of the town of Newbury into a new town by the name of Newburyport." The act begins:Whereas the town of Newbury is large, the inhabitants of that part of it who dwell by the water-side there, as it is called, are merchants and artificers, the inhabitants of the other parts of the town are chiefly husbandmen. That that part of the said town of Newbury... be and hereby are constituted and made a separate and distinct town.... The act was approved by Governor Francis Bernard on February 4, 1764; the new town was the smallest in Massachusetts, covering an area of 647 acres, had a population of 2,800 living in 357 homes. There were three shipyards, no bridges, several ferries, one of which at the foot of Greenleaf Lane, now State Street, carried the Portsmouth Flying Stage Coach, running between Portsmouth, New Hampshire, Boston; the town prospered and became a city in 1851.
Situated near the mouth of the Merrimack River, it was once a fishing and shipping center, with an industry in silverware manufacture. In 1792, a bridge was built two miles above the town. Merrimack Arms and Brown Manufacturing Company made Southerner Derringer pistols in their Newburyport factory from 1867 to 1873; the captains of old Newburyport had participated vigorously in the triangular trade, importing West Indian molasses and exporting rum made from it. The distilleries were located around Market Square near the waterfront. Caldwell's Old Newburyport rum was manufactured locally until well into the 19th century. Although the purchase of slaves in Massachusetts was illegal, ownership of slaves purchased elsewhere was not. Newburyport prior to the Civil War had always been divided over slavery. While many of its leading citizens profited from and defended slavery, it had been a frequent topic of pulpit rhetoric. After the Revolutionary War, abolitionism took a firm hold, Newburyport included.
Several citizens are recognized by the National Park Service for their contributions to the Underground Railroad. The abolitionist movement reached a peak with the activities of William Lloyd Garrison, born in Newburyport and helped develop an anti-slavery climate. In 1841, Garrison was imprisoned on charges of libel for accusing Newburyport shipowner Francis Todd and captain Nicholas Brown of transporting 44 African captives in chains, his statue stands in Brown Square, the scene of abolitionist meetings. Newburyport once had a fishing fleet that operated from Georges Bank to the mouth of the Merrimack River, it was a center for privateering during the Revolutionary War and War of 1812. Beginning about 1832, it added numerous ships to the whaling fleet. Clipper ships were built there. Today, the city gives little hint of its former maritime importance. Notably missing are the docks, which are shown on earlier maps extending into the channel of the Merrimack River, the shipyards, where the waterfront parking lot is located.
George Whitefield, the well-known and influential English preacher who helped inspire the First Great Awakening in America, arrived in Newburyport in September 1740. The revival that followed his labors, brought into existence Old South Church, where he was buried after his death in 1770; the city's historical highlights include: Historic events: First of many subsequent clipper ships built here First "Tea Party" rebellion to oppose British Tea Tax First state mint and treasury building Newburyport Superior Courthouse, the oldest continuously active courthouse in MassachusettsThe Newburyport Five Cents Savings Bank on State Street was founded in 1854, is one of the oldest banks in the United States still in operation. Historic houses and museums: Cushing House Museum & Garden Newburyport Custom House Museum, designed by Robert MillsLiterary interests: Was referred to in the H. P. Lovecraft story, "The Shadow Over Innsmouth", as being located near Innsmouth. Lovecraft in fact based his depiction of Innsmouth on Newburyport.
Subject of the most ambitious community study undertaken, the Yankee City project conducted by anthropologist W. Lloyd Warner and his associates Despite its former prosperi
South Eastern Railway (England)
The South Eastern Railway was a railway company in south-eastern England from 1836 until 1922. The company was formed to construct a route from London to Dover. Branch lines were opened to Tunbridge Wells, Hastings and other places in Kent; the SER absorbed or leased other railways, some older than itself, including the London and Greenwich Railway and the Canterbury and Whitstable Railway. Most of the company's routes were in Kent, eastern Sussex and the London suburbs, with a long cross-country route from Redhill in Surrey to Reading, Berkshire. Much of the company's early history saw attempts at feuding with its neighbours. However, in 1899 the SER agreed with the LCDR to share operation of the two railways, work them as a single system and pool receipts: but it was not a full amalgamation; the SER and LCDR remained separate companies until becoming constituents of the Southern Railway on 1 January 1923. There had been proposals for a railway between London and Dover in 1825, 1832 and 1835, but they came to nothing due to opposition from landowners or the difficulties of bridging the River Medway near its mouth.
On 21 June 1836, the Parliament of the United Kingdom passed a Private Act incorporating the South Eastern and Dover Railway, which shortly afterwards changed to the South Eastern Railway. At the time of inauguration there were two potential rail pathways south from London, the Speaker of the House of Commons had said no further pathways would be permitted; the SER therefore considered routes to Dover from the proposed London and Southampton Railway line at Wimbledon, or from the existing London and Greenwich Railway at Greenwich. The former left London in the wrong direction and on a roundabout route; the latter provided a useful way for a northern route via Gravesend and Canterbury, except that lengthening the line beyond Greenwich was blocked by opposition from the Admiralty, this route would involve tunnelling through the North Downs. The engineer of the new line, William Cubitt, was engineer of the London and Croydon Railway, which planned to use L&GR lines as far as Corbett’s Lane in Bermondsey before turning south towards Croydon.
A new connection on this line near to Norwood could provide access to a southerly route to Dover via Tonbridge and Folkestone. This was less direct than the northerly route but passed through easier country, it involved one significant 1,387-yard tunnel through the Shakespeare Cliff near Dover. This was the route first chosen by the SER at its inauguration. During Parliamentary discussions on the proposed route of the London and Brighton Railway during 1837, pressure was put on the SER to divert its proposed route so it could share the L&BR mainline between Jolly Sailor and Earlswood Common, travel eastwards to Tonbridge. Under the scheme proposed by Parliament, the railway from Croydon to Redhill would be built by the L&BR but the SER would have the right to refund half the construction costs and own that part of the line between Merstham and Redhill; the SER gave way to this proposal as it reduced the construction costs, although it resulted in a route 20 miles longer than by road, running south for 14.5 miles and turning east.
It meant that its trains from London Bridge passed over the lines of three other companies: the L&GR to Corbett's Lane Junction, the L&CR as far as'Jolly Sailor', the L&BR to Merstham. Construction began in 1838 at several places and the Shakespeare Tunnel was complete by May 1841; the L&BR line to Redhill opened on 12 July 1841 and the SER line from Redhill to Tonbridge on 26 May 1842, when SER train services began. The main line reached Ashford on 1 December 1842. On the same day the SER offered to lease the L&BR for 21 years at £100,000 per year, but the offer was turned down; that year, the SER refunded to the L&BR £430,000 and took ownership of the southern half of the Croydon-Redhill line. Trains ran toll-free to both companies on this stretch but still had pay on the L&CR from Norwood Junction railway station to Corbett's Lane Junction, the L&GR into London Bridge. In 1843, when the railway reached the edge of Folkestone, the company bought the silted and nearly derelict harbour, built by Thomas Telford in 1809, for £18,000.
The SER dredged the harbour and, after a trial with the paddle steamer Water Witch, which demonstrated that a day excursion from London to Boulogne was feasible, arranged for a packet company to provide a ferry to Boulogne. The following year it established the independent South Eastern & Continental Steam Packet Company, which it absorbed in 1853. James Broadbridge Monger was the Master of the "Water Witch" from 1839 to 1844. From 1844 on, he was Master of three vessels which steamed from Dover and Folkstone to Boulogne and Ostend with passengers and cargo: "Lord Warden", "Princess Helena" and "Princess Maude". In December 1848 it opened a steeply graded branch from the Folkestone station to the harbour; the SER opened Dover station on 7 February 1844. This was a terminus, but in 1860 the line was continued to Admiralty Pier. Thereafter the SER concentrated most of its resources into developing Folkestone Harbour, which became its principal base for cross-channel ferries; the company had complete control of Folkestone whereas at Dover it had to negotiate with both the Admiralty and the local town council, the rail route from Boulogne to Paris was better developed than that from Calai
A patent is a form of intellectual property. A patent gives its owner the right to exclude others from making, using and importing an invention for a limited period of time twenty years; the patent rights are granted in exchange for an enabling public disclosure of the invention. In most countries patent rights fall under civil law and the patent holder needs to sue someone infringing the patent in order to enforce his or her rights. In some industries patents are an essential form of competitive advantage; the procedure for granting patents, requirements placed on the patentee, the extent of the exclusive rights vary between countries according to national laws and international agreements. However, a granted patent application must include one or more claims that define the invention. A patent may include many claims; these claims must meet relevant patentability requirements, such as novelty and non-obviousness. Under the World Trade Organization's TRIPS Agreement, patents should be available in WTO member states for any invention, in all fields of technology, provided they are new, involve an inventive step, are capable of industrial application.
There are variations on what is patentable subject matter from country to country among WTO member states. TRIPS provides that the term of protection available should be a minimum of twenty years; the word patent originates from the Latin patere, which means "to lay open". It is a shortened version of the term letters patent, an open document or instrument issued by a monarch or government granting exclusive rights to a person, predating the modern patent system. Similar grants included land patents, which were land grants by early state governments in the USA, printing patents, a precursor of modern copyright. In modern usage, the term patent refers to the right granted to anyone who invents something new and non-obvious; some other types of intellectual property rights are called patents in some jurisdictions: industrial design rights are called design patents in the US, plant breeders' rights are sometimes called plant patents, utility models and Gebrauchsmuster are sometimes called petty patents or innovation patents.
The additional qualification utility patent is sometimes used to distinguish the primary meaning from these other types of patents. Particular species of patents for inventions include biological patents, business method patents, chemical patents and software patents. Although there is some evidence that some form of patent rights was recognized in Ancient Greece in the Greek city of Sybaris, the first statutory patent system is regarded to be the Venetian Patent Statute of 1474. Patents were systematically granted in Venice as of 1474, where they issued a decree by which new and inventive devices had to be communicated to the Republic in order to obtain legal protection against potential infringers; the period of protection was 10 years.. As Venetians emigrated, they sought similar patent protection in their new homes; this led to the diffusion of patent systems to other countries. The English patent system evolved from its early medieval origins into the first modern patent system that recognised intellectual property in order to stimulate invention.
By the 16th century, the English Crown would habitually abuse the granting of letters patent for monopolies. After public outcry, King James I of England was forced to revoke all existing monopolies and declare that they were only to be used for "projects of new invention"; this was incorporated into the Statute of Monopolies in which Parliament restricted the Crown's power explicitly so that the King could only issue letters patent to the inventors or introducers of original inventions for a fixed number of years. The Statute became the foundation for developments in patent law in England and elsewhere. Important developments in patent law emerged during the 18th century through a slow process of judicial interpretation of the law. During the reign of Queen Anne, patent applications were required to supply a complete specification of the principles of operation of the invention for public access. Legal battles around the 1796 patent taken out by James Watt for his steam engine, established the principles that patents could be issued for improvements of an existing machine and that ideas or principles without specific practical application could legally be patented.
Influenced by the philosophy of John Locke, the granting of patents began to be viewed as a form of intellectual property right, rather than the obtaining of economic privilege. The English legal system became the foundation for patent law in countries with a common law heritage, including the United States, New Zealand and Australia. In the Thirteen Colonies, inventors could obtain patents through petition to a given colony's legislature. In 1641, Samuel Winslow was granted the first patent in North America by the Massachusetts General Court for a new process for making salt; the modern French patent system was created during the Revolution in 1791. Patents were granted without examination. Patent costs were high. Importation patents protected new devices coming from foreign countries; the patent law was revised in 1844 - patent cost was lowered and importation patents were abolished. The first Patent Act of the U. S. Congress was passed on April 10, 1790, titled "An Act to promote the progress of
A machine gun is a automatic mounted or portable firearm designed to fire rifle cartridges in rapid succession from an ammunition belt or magazine for the purpose of suppressive fire. Not all automatic firearms are machine guns. Submachine guns, assault rifles, battle rifles, pistols or cannons may be capable of automatic fire, but are not designed for sustained fire; as a class of military rapid-fire guns, machine guns are automatic weapons designed to be used as support weapons and used when attached to a mount- or fired from the ground on a bipod or tripod. Many machine guns use belt feeding and open bolt operation, features not found on rifles. In the U. S. A, a "machine gun" is a legal term for any weapon able to fire more than one shot per function of the trigger regardless of caliber, the receiver of any such weapon, any weapon convertible to such a state using normal tools, or any component or part that will modify an existing firearm such that it functions as a "machine gun" such as a drop-in auto sear.
Civilian possession of such weapons manufactured prior to 1986 is not prohibited by any federal law and not illegal in many states, but they must be registered as Title II weapons under the National Firearms Act and have a tax stamp paid. Machine guns manufactured after 1986 are prohibited by the Hughes Amendment to the Gun Owners Protection Act. Unlike semi-automatic firearms, which require one trigger pull per round fired, a machine gun is designed to fire for as long as the trigger is held down. Nowadays the term is restricted to heavy weapons, able to provide continuous or frequent bursts of automatic fire for as long as ammunition lasts. Machine guns are used against personnel and light vehicles, or to provide suppressive fire, either directly or indirectly, they are mounted on fast attack vehicles such as technicals to provide heavy mobile firepower, armored vehicles such as tanks for engaging targets too small to justify use of the primary weaponry or too fast to engage with it, on aircraft as defensive armament or for strafing ground targets, though on fighter aircraft true machine guns have been supplanted by large-caliber rotary guns.
Some machine guns have in practice sustained fire continuously for hours. Because they become hot all machine guns fire from an open bolt, to permit air cooling from the breech between bursts, they usually have either a barrel cooling system, slow-heating heavyweight barrel, or removable barrels which allow a hot barrel to be replaced. Although subdivided into "light", "medium", "heavy" or "general-purpose" the lightest machine guns tend to be larger and heavier than standard infantry arms. Medium and heavy machine guns are either mounted on a vehicle. Light machine guns are designed to provide mobile fire support to a squad and are air-cooled weapons fitted with a box magazine or drum and a bipod. Medium machine guns use full-sized rifle rounds and are designed to be used from fixed positions mounted on a tripod. Heavy machine gun is a term originating in World War I to describe heavyweight medium machine guns and persisted into World War II with Japanese Hotchkiss M1914 clones. A general-purpose machine gun is a lightweight medium machine gun which can either be used with a bipod and drum in the light machine gun role or a tripod and belt feed in the medium machine gun role.
Machine guns have simple iron sights, though the use of optics is becoming more common. A common aiming system for direct fire is to alternate solid rounds and tracer ammunition rounds, so shooters can see the trajectory and "walk" the fire into the target, direct the fire of other soldiers. Many heavy machine guns, such as the Browning M2.50 caliber machine gun, are accurate enough to engage targets at great distances. During the Vietnam War, Carlos Hathcock set the record for a long-distance shot at 7,382 ft with a.50 caliber heavy machine gun he had equipped with a telescopic sight. This led to the introduction of.50 caliber anti-materiel sniper rifles, such as the Barrett M82. Other automatic weapons are subdivided into several categories based on the size of the bullet used, whether the cartridge is fired from a closed bolt or an open bolt, whether the action used is locked or is some form of blowback. Automatic firearms using pistol-calibre ammunition are called machine pistols or submachine guns on the basis of size.
The term personal defense weapon is sometimes applied to weapons firing dedicated armor-piercing rounds which would otherwise be regarded as machine pistols or SMGs, but it is not strongly defined and has been used to describe a range of weapons from ordinary SMGs to compact assault rifles. Selective fire rifles firing a full-power rifle cartridge from a closed bolt are called automatic rifles or battle rifles, while rifles that fire an intermediate cartridge are called assault rifles. Assault rifles are a compromise between the size and weight of a pistol-calibre submachine gun and a full size battle rifle, firing intermediate cartridges and allowing semi-automatic and burst or full-automatic fire options
A postage stamp is a small piece of paper issued by a post office, postal administration, or other authorized vendors to customers who pay postage, who affix the stamp to the face or address-side of any item of mail—an envelope or other postal cover —that they wish to send. The item is processed by the postal system, where a postmark or cancellation mark—in modern usage indicating date and point of origin of mailing—is applied to the stamp and its left and right sides to prevent its reuse; the item is delivered to its addressee. Always featuring the name of the issuing nation, a denomination of its value, an illustration of persons, institutions, or natural realities that symbolize the nation's traditions and values, every stamp is printed on a piece of rectangular, but sometimes triangular or otherwise shaped special custom-made paper whose back is either glazed with an adhesive gum or self-adhesive; because governments issue stamps of different denominations in unequal numbers and discontinue some lines and introduce others, because of their illustrations and association with the social and political realities of the time of their issue, they are prized for their beauty and historical significance by stamp collectors whose study of their history and of mailing systems is called philately.
Because collectors buy stamps from an issuing agency with no intention to use them for postage, the revenues from such purchases and payments of postage can make them a source of net profit to that agency. Throughout modern history, numerous methods were used to indicate that postage had been paid on a mailed item, so several different men have received credit for inventing the postage stamp. William DockwraIn 1680, William Dockwra, an English merchant in London, his partner Robert Murray established the London Penny Post, a mail system that delivered letters and small parcels inside the city of London for the sum of one penny. Confirmation of paid postage was indicated by the use of a hand stamp to frank the mailed item. Though this'stamp' was applied to the letter or parcel itself, rather than to a separate piece of paper, it is considered by many historians to be the world's first postage stamp. Lovrenc KoširIn 1835, the Slovene civil servant Lovrenc Košir from Ljubljana in Austria-Hungary, suggested the use of "artificially affixed postal tax stamps" using "gepresste papieroblate", but although civil bureaucrats considered the suggestion in detail, it was not adopted.
Rowland HillIn 1836, a Member of Parliament, Robert Wallace, gave Sir Rowland Hill numerous books and documents about the postal service, which Hill described as a "half hundred weight of material". After a detailed study, on 4 January 1837 Hill submitted a pamphlet entitled Post Office Reform: Its Importance and Practicability, marked "private and confidential," and not released to the general public, to the Chancellor of the Exchequer, Thomas Spring Rice; the Chancellor summoned Hill to a meeting at which he suggested improvements and changes to be presented in a supplement, which Hill duly produced and submitted on 28 January 1837. Summoned to give evidence before the Commission for Post Office Enquiry on 13 February 1837, Hill read from the letter he wrote to the Chancellor that included a statement saying that the notation of paid postage could be created "...by using a bit of paper just large enough to bear the stamp, covered at the back with a glutinous wash...". This would become the first unambiguous description of a modern adhesive postage stamp.
Shortly afterward, Hill's revision of the booklet, dated 22 February 1837, containing some 28,000 words, incorporating the supplement given to the Chancellor and statements he made to the Commission, was published and made available to the general public. Hansard records that on 15 December 1837, Benjamin Hawes asked the Chancellor of the Exchequer "whether it was the intention of the Government to give effect to the recommendation of the Commissioners of the Post-office, contained in their ninth report relating to the reduction of the rates of postage, the issuing of penny stamps?"Hill’s ideas for postage stamps and charging paid-postage based on weight soon took hold, were adopted in many countries throughout the world. With the new policy of charging by weight, using envelopes for mailing documents became the norm. Hill’s brother Edwin invented a prototype envelope-making machine that folded paper into envelopes enough to match the pace of the growing demand for postage stamps. Rowland Hill and the reforms he introduced to the United Kingdom postal system appear on several of its commemorative stamps.
James ChalmersIn the 1881 book The Penny Postage Scheme of 1837, Scotsman Patrick Chalmers claimed that his father, James Chalmers, published an essay in August 1834 describing and advocating a postage stamp, but submitted no evidence of the essay's existence. Until he died in 1891, Patrick Chalmers campaigned to have his father recognized as the inventor of the postage stamp; the first independent evidence for Chalmers' claim is an essay, dated 8 February 1838 and received by the Post Office on 17 February 1838, in which he proposed adhesive postage stamps to the General Post Office. In this 800-word document concerning methods of indicating that postage had been paid on mail he states: "Therefore, of Mr Hill’s plan of a uniform rate of postage... I conceive that the most simple and economical mode... would be by Slips... in the hope that Mr Hill’s plan may soon be carried into operation I would sugg