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Samuel Brown ( -1849) was an English engineer and inventor credited with developing one of the earliest examples of an internal combustion engine, during the early 19th century.
Brown was a cooper by training (he also patented improvements to machinery for manufacturing casks and other vessels), has been described as the 'father of the gas engine'.
While living at Eagle Lodge in the Brompton area of west London, from 1825 to 1835, he developed 'the first gas engine that unquestionably did actual work and was a mechanical success'. He set up two engines for demonstration purposes in the grounds of the Lodge.
1823. In patents dated 4 December 1823 and 22 April 1826, Brown proposed to fill a closed chamber with a gas flame, and so expel the air; then he condensed the flame by injecting water, and operated an air engine by exhausting into the partial vacuum so obtained. The idea was evidently suggested by James Watt's condensing steam engine, flame being employed instead of steam to obtain a vacuum. 
Brown designed an engine that used hydrogen as a fuel - an early example of an internal combustion engine. It had separate combustion and working cylinders, and was cooled by water contained within a casing or cylinder lining, circulated around the cylinders (water was constantly kept moving through the action of a pump and was re-cooled by contact with outside air). It had a capacity of 8,800 cc but was rated at only 4 hp. He tested the engine by using it to propel a vehicle up Shooter's Hill on 27 May 1826.
1826 "In 1826, Mr. Samuel Brown applied his gas-vacuum engine ... to a carriage, and ascended Shooter's hill to the satisfaction of numerous spectators. The great expense, however, which attended the working of a gas-vacuum engine, prevented its adoption."
1827 Trials on a launch on the Thames were made, but the results were not considered profitable. See below.
1827 'MR. BROWN'S GAS ENGINE. We mentioned some time since, that a temporary trial of this engine took place between Blackfriars’ Bridge and Southwark Bridge, and that as far as it went the result was quite satisfactory. Yesterday a more extended exhibition took place in the presence of several scientific men ; some extensive coach proprietors were also present. The bridge and the avenues leading it were crowded with spectators. At one o’clock, the boat (containing nine gentlemen, and the three men who worked the engine, steered, and attended to the anchor) proceeded rapidly down the river, with a strong ebb tide, and coming near the Iron Bridge, she put about, and was admirably worked up through the centre arch of Blackfriars’ Bridge, against a very heavy fall of water. We were much pleased with the steady and effective manner in which the boat was propelled, as well as with the quiet and regular motion of the machinery. Several gentlemen, who had previously entertained some doubts, now expressed their conviction of its perfect applicabilily as a propelling power, for all purposes of land and water carriage. One great coach proprietor, after minutely examining the whole of the apparatus, in company with a scientific friend, expressed himself pertectly satisfied with the power, safety, and portability and said he was determined to enter into contracts for running carriages with engines of that construction, considering it superior to any other he had seen.'
1828 'We were much gratified a day or two ago by witnessing a novel exhibition on the Hammersmith road of a large carriage propelled by a Gas Vacuum Engine, which rolled along with great ease, at the rate of seven miles per hour. There were several gentlemen in and upon it, who appeared quite satisfied of its power and safety. The public are indebted to Samuel Brown, Esq. of Brompton, for this valuable discovery, who has been indefatigable in his exertions to bring it to its present state of perfection!'
1831 'Mr. Samuel Brown, of Eagle Lodge, Brompton, Middlesex, takes this opportunity of informing all persons interested in Drainage, that he has erected one of his PATENT GAS ENGINES in Soham Meer, within about a mile and a half of the town of Soham, in this county, and that the same will be at work for the inspection of the public on Wednesday the 19th day of January instant, at 12 o'clock at noon'
1832 August. Letter to Mechanics' Magazine concerning the engine. Addressed from Eagle Lodge.
The engine was also employed to pump water and to propel river boats. Brown formed a company to produce engines for boats and barges, one of which is said to have achieved a speed of 8 mph upstream.
The company was unsuccessful, although this may have been due concerns about obtaining adequate supplies of the gas fuel rather than concerns about the engines.
In 1844 Brown was one of several expert witnesses at a court case concerning the priority of a screw propeller patent (Lowe v. Penn). 'Samuel Brown said,- I was employed in 1825 to make a gas engine propeller, to be placed on board a canal boat. I had used a screw to propel vessels in 1824. It was situated at the stern. I found that the whole screw would not answer, and I cut off piece by piece, until I arrived at the conclusion that a segment of a screw was better for propelling than a whole screw. I fitted up a vessel, for which I received £300 from the company by which I was employed to fit it up. The boat was worked on the river, and hundreds of persons examined it, and I had a model on board to explain the principle to everybody who came. That's how it got abroad. My axis worked in a stuffing box under the water.'
1849, 16th September: Death announcement: '.... at Bermondsey, Samuel Brown, Esq., late of Gravel-lane, London, the celebrated inventor of the gas vacuum engine, the screw propeller, &c.'
A comprehensive article about Brown and his work was published in 'The Engineer' in 1946. Reference is made to the fact that a small public library had been built on, or adjacent to, the site of Eagle Lodge. The article's author proposed that a plaque should be erected there to proclaim 'Here laboured Samuel Brown who devised the first internal combustion engine which ever did actual industrial work'.
A Newcomen Society Paper presented in 2011 provides a good summary of Brown's engines, with illustrations of three types.