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George Medhurst (1759-1827), Civil Engineer of Denmark Street, London, inventor of the Atmospheric Railway
1759 Baptised at Shoreham, Kent, the son of George and Anne Medhurst.
Clockmaker at Pleasant Row, Clerkenwell,
1797 After the imposition of a duty on clocks had depressed trade, he turned to engineering, working at Battle Bridge, Clerkenwell.
1799 Patent granted "a condensing wind-engine, capable of being applied to all kinds of purposes, in which steam, water, wind, or horses are employed." 
By about 1800 Medhurst had established himself at 1 Denmark Street, Westminster, as a maker of scales and weighing machines, machinist, and ironfounder. Made heavy duty platforms for weighing goods in sacks, cases, or carts, and for weighing jockeys.
1800 Patented his Aeolian engine, by which a carriage could be propelled by compressed air contained in a reservoir beneath the vehicle. He also described an engine worked by gas produced by exploding small quantities of gunpowder at regular intervals in the cylinder.
1801 Medhurst patented a compound crank for converting rotary into rectilinear motion and in the same year took over the patent rights for a washing and wringing machine devised by James Wood in 1790.
By 1810 he had invented and built a steam carriage which ran successfully. Also invented some balancing scales used by shopkeepers.
1810 Published but did not patent 'A New Method of Conveying Letters and Goods with Great Certainty and Rapidity by Air'. This described a pneumatic railway consisting of an iron tube six feet high and five feet wide fitted with rails and able to take carriages by using compressed air behind them.
1812 Issued a refinement to the design
1817 Patented an equal balance weighing machine used widely in shops. 'George Medhurst, of Denmark-street, St Giles in the Fields, Middlesex, engineer, for an arrangement of implements to form certain apparatus, which he denominates the Hydraulic Balance, applicable to mechanical and hydraulic purposes. August 26.'
1820 Medhurst's steam carriage carried one man between Paddington and Islington on 3 April and again on 6 July.
1821 A more substantial carriage ran up and down Paddington Hill at 5 m.p.h.
By 1827 Medhurst was offering to sell a carriage able to carry four persons at 7 m.p.h.
1827 Advertised his patent canal lock, to prevent loss of water, and a leak proof lock gate, though no patents were filed under his name.
1827 Issued a further pamphlet on the design (of the railway?) using water
1830 Some reference to his 1799 patent granted
1937 Mentioned in a letter to 'The Times' 
DNB Biography (First series)
MEDHURST, GEORGE (1759-1827), engineer and projector of the atmospheric railway, born at Shoreham, Kent, where he was baptised on 11 Feb. 1759, was son of George and Anne Medhurst.
He was brought up as a clockmaker, and carried on business for a time in Pleasant Row, Clerkenwell; but the imposition of a duty on clocks in 1797 inflicted great injury upon his trade, and about 1799 he started as an engineer at Battle Bridge.
In the year last mentioned he obtained a patent (No. 2299) for 'a wind-mill and pumps for compressing air for obtaining motive power.' The sails of the windmill were arranged in the manner now generally followed in the construction of small windmills for pumping water. The pumping machinery shows great ingenuity, a governor being attached to vary the length of stroke of the pump, according to the strength of the wind and the pressure of the air in the reservoir. Medhurst's idea was to avail himself of the wind, whenever it served, to compress large bodies of air for use when required, and he worked steadily at the subject to the end of his life. The specification also contains a description of a small rotary engine to be worked by compressed air.
In the following year he patented his 'Eolian engine' (No. 2431), in which he describes other machinery for compressing air, and shows how carriages may be driven upon common roads by compressed air contained in a reservoir underneath the vehicle. He contemplated the establishment of regular lines of coaches, with pumping stations at the end of each stage for replenishing the reservoirs.
He also describes an engine worked by gas produced by the explosion in the cylinder of small quantities of gunpowder at regular intervals. He endeavoured to form a company, with a capital of £50,000 to work this invention, and published a pamphlet 'On the Properties, Power, and Applications of the Eolian Engine, with a Plan of the Particulars for carrying it into Execution,' London, n.d., 8vo, pp. 19. he calculated that a vessel of sixteen cubic feet capacity, containing compressed air of sixteen atmospheres, would suffice to do the work of one horse for an hour.
In 1801 he patented a 'compound crank for converting rotary into rectilinear motion'. It is not quite certain whether the George Medhurst to whom a patent (No. 2525) for a washing and wringing machine was granted in the same year is identical with the subject of this memoir, as he is described as 'a mathematical instrument maker, of Pentonville.'
About the beginning of the century Medhurst established himself as a machinist and ironfounder at Denmark Street, Soho, where the concern was carried on by his successors until a few years ago. He turned his attention to weighing machines and scales, and was the inventor of the the equal balance weighing machine now in universal use, as well as of the scales which are to be found in almost every retail shop.
Medhurst was the first to suggest the 'pneumatic dispatch,' as it has since been called. This was not patented, his proposals being made public in 'A New Method of Conveying Letters and Goods with great Certainty and Rapidity by Air,' London, 1810. He proposed to convey small parcels or letters in tubes by compressed air, and heavy goods to the weight of a ton and a half through brick tunnels, which the carriage just fitted.
In 1812 he published 'Calculations and Remarks tending to prove the Practicability, Effects and Advantages of a Plan for the Rapid Conveyance of Passengers upon an Iron Railway, through a Tube of Thirty Feet in Area, by the Power and Velocity of Air/ London, 1812, 8vo, pp. 19. He argued that an average speed of fifty miles an hour might be attained, and that passengers might be conveyed at a cost of a farthing per mile, and goods at a penny per ton per mile. The passengers were to travel inside the tunnel, but he hints at the possibility of driving a carriage on rails in the open air by means of a piston in a continuous tube between the rails. This was long afterwards known as the atmospheric railway.
The subject was further developed in 'A new System of Inland Conveyance for Goods and Passengers capable of being applied and extended throughout the Country, and of Conveying all kinds of Goods and Passengers with the Velocity of Sixty Miles in an Hour'. London, 1827, 8vo, pp. 38. This pamphlet contains several illustrations showing the pumping engines and the details of the valve for opening and closing the longitudinal slit in the tube, a difficulty which has never yet been overcome, and has been the cause of failure of all the atmospheric railways hitherto tried. It does not appear that Medhurst had the opportunity of putting any of his schemes into practice, but he had a very clear conception of the conditions of the problem of atmospheric propulsion. He laid his plans before the post-office authorities, but the reply was not encouraging.
He is also said to have invented a one-wheel clock, and to have been the actual inventor of the box-mangle, long known as 'Baker's patent mangle' though no patent was obtained. Medhurst is occasionally referred to as a Dane, but this arose from the blunder of a French writer, who was misled by the address 'Denmark Street' (see Mechanics' Magazine, 1844, xli. 141). Copies of Medhurst's publications are exceedingly rare, but a complete set is to be found in the library of the Institution of Civil Engineers, Westminster.
Medhurst died in September 1827, and was buried at Shoreham on 10 Sept.
[The personal details in the above notice are based upon information supplied by Mr. Thomas Medhurst, grandson of George Medhurst.]