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1831 April 7th. Born in Kincardine, Scotland, the son of a draper.
He left home and moved to Edinburgh where he worked as an apprentice while studying the Hebrew and Greek languages, mathematics and mechanics.
Moved to Paisley where he worked for Mr. Blackwood, later a partner in Blackwood and Gordon.
He next obtained a position with McNab's marine engineering works in Greenock and worked as an engineer, and was rapidly promoted.
He returned to Blackwood and Gordon's, which had now moved to Port Glasgow. His employers recommended him for a position as chief draftsman and manager at the George Forrester and Company engineering works in Liverpool.
About 1855 Gray saw a large gyroscope being exhibited by Sir William Armstrong at the Newcastle Philosophical Institution, and spent some time working out exactly how it worked. He later explained the engineering principles to the officers of the Board of Trade. According the The Nautical Magazine, "so far as we are aware, the first example of direct calculation of gyroscopic effect as an engineering quality is due to Gray, and made in relation to strains resulting from rolling and pitching on the shafts of fly-wheels attached to marine engines.
At Forrester's Gray designed marine engines and various types of machinery.
In 1866 he patented a steam steering engine that incorporated feedback, first used in the SS Great Eastern, the largest and most advanced ship of the day. This brought him acclaim in the engineering world.
At that time as many as a hundred men might be needed to work the steering gear in an armoured cruiser moving at full speed. Gray was asked to look into using steam power for the steering gears. The invention was first tried in March 1867. The trial was successful and the steam steering gear was generally adopted. Gray said of the steering device much later- "The principal thing that I did was to make an automatic controlling valve, continuous in its action. To put a handle to where you wanted something to move had been done before, but I saw that it would not do for steering. I therefore contrived the differential movement of the reversing vale, but [by?] which the rudder or other object to be moved would be made to follow the movement of the controlling wheel or lever."
In Gray's invention the angle of the rudder is transmitted to a differential screw, which in turn controls a steam valve that supplies power to a motor that turns the rudder. As the rudder approaches the desired angle indicated by the helm the steam valve is adjusted to reduce power. If it moves away from that angle the valve opens to increase power and return the rudder to its position. Gray had invented a servomechanism, a name coined by the French engineer Jean Joseph Léon Farcot. Farcot must be given equal credit for the concept, which he had developed independently.
Gray became a member of the Institution of Mechanical Engineers in 1865. He also became a member of the Royal Institution of Naval Architects. He was a Vice-President of the Institute of Marine Engineers from its foundation in 1889.
Gray wanted engineers to act according to the importance of their position. He said, "If engineers will aim at so conducting themselves that they are never spoken of otherwise as being 'quite equal if not superior to the deck officers in their language and behaviour', and if that pertains to their highly intellectual calling that makes themselves masters both of theory and the practice, the time would not be very distant when their importance in steamers would be fully recognized."
Gray was employed by the Board of Trade in Liverpool, then in Cork and finally in London, where he was appointed chief examiner of marine engineers. In this position his influence was limited since Board of Trade policy did not allow publication of the individual opinions of their engineering officers, but he was able to present some theoretical papers at meetings of engineers.
He was instrumental in introducing the use of entropy-temperature diagrams, described by Professor Josiah Willard Gibbs, into use for solving steam engine problems. He retired in 1906 and settled in Edinburgh.
1908 January 14th. Died aged 76.
1908 March 20th. Probate. John Macfarlane Gray of 11 Spottiswood Road, Edinburgh to George Macfarlane Gray, surveyor.
Around 1885 Gray wrote a report about the second law of thermo-dynamics that caused some controversy. The Council of the Royal Society declined to allow him to read the report before the Society. The society first asked for more information about his investigations. However, he read papers on the subject before the Physical Society and the Institution of Naval Architects, and planned to publish a book giving the results of his researches into thermodynamics.
Gray presented papers on theoretical subjects related to steam power that included:
1908 Obituary 
JOHN MACFARLANE GRAY was born at Kincardine on 7th April 1831, being the son of a draper of that town. Not wishing to follow his father's business, he left home and became an apprentice with Mr. Slight, of Leith Walk, Edinburgh, and while there continued his studios, which included Hebrew and Greek, mathematics and mechanics.
Later he went to Paisley, working with Mr. Blackwood, subsequently of Blackwood and Gordon.
Thence he proceeded to McNab's marine engineering works at Greenock, and there he had practically his first opportunity of utilising the results of his study, with the consequence that his promotion was rapid.
He was next at Blackwood and Gordon's, now at Port Glasgow, and it was from there that he was recommended for the post of chief draughtsman and manager at Messrs. George Forrester and Co.'s engineering works at Liverpool. At these works he was engaged in designing marine engines and machinery of various types, but perhaps the most important work done there, and which brought him first into prominence, was the invention of the steam steering-gear in 1866, which was first applied to the "Great Eastern."
As he narrated in a Paper a read before this Institution difficulties bad arisen in several ships. In an armoured cruiser a hundred men were sometimes required to work the gear when the ship was running at full speed. A serious accident, too, had happened on the "Great Eastern," and he was asked to go into the problem of applying steam to supersede manual work.
The first trial of his differential gear on that steamer was made in March 1867, and proved successful, leading eventually to the general adoption of the system.
It was at Liverpool that he first became associated with the Board of Trade. Then he went to Cork, where his only son — Mr. George Macfarlane Gray — now occupies the same position of Board of Trade surveyor.
Ultimately he was drafted to London to be consulted by the Board of Trade regarding scientific matters, and then became chief examiner of marine engineers.
His early struggles fitted him admirably for the position. He could read character as well as a mathematical test-paper, and he could differentiate between the slips duo to excitement and the errors of ignorance. By an official rule of the Board of Trade, which prevented the individual opinion of any of their engineering officers being made public, much of his influence in regard to science was seriously limited. Fortunately, he had been able to disclose the results of his investigation on the Theta-Phi diagram in a Paper rend before the Institution of Naval Architects in 1885 on "The Theoretical Duty of Heat in the Steam-Engine."
This was followed in 1889 by his Paper read at this Institution on "The Ether-Pressure Theory of Thermodynamics applied to Steam."
At the Paris Meeting in the same year he read probably his most illuminative, although abstruse, Paper on the theory "The Rationalization of Regnault's Experiments on Steam." In this be described and explained the use of the steam and waterlines of the temperature-entropy diagram.
The death of his friend, Mr. P. W. Willans, in 1892, was an irreparable loss to him. The investigations carried out by them were in the interests of science, and confirmed in practice much that Mr. Gray held to be true in theory.
His next contribution, also confirmatory of his theory, was to the Royal Society in January 1900, when he analysed the experiments of Grindley on the cooling of saturated steam by free expansion.
His latest and most comprehensive review of the whole subject was contained in a Paper contributed to the Institution of Civil Engineers in 1901, on "Variable and Absolute Specific Heats of Water." For this be was awarded a Telford Medal, although he was not a Member.
Besides contributing the above-mentioned Papers, he was a frequent attendant at meetings of the various technical societies, sometimes taking part in the discussions.
In 1906 he retired to Edinburgh to spend the remaining years of his life. Although he maintained remarkable vitality and unimpaired mental capability, he suffered much from an internal malady, and his death took place in Edinburgh on 14th January 1908, in his seventy-seventh year.
As with most men, the circumstances of his early life and training greatly influenced his future, and especially his mental attitude towards most problems. He was a self-trained man, inclined to isolation in his investigations, keenly critical and outspoken.
He became a Member of this Institution in 1865. He was also a Member of the Institution of Naval Architects, of which he was a Member of Council from 1880, and a Vice-President from 1904. He was a Vice-President of the Institute of Marine Engineers from its inception in 1889.
Obituary 1909 
. . . for some time had been the chief examiner of engineers for the Board of Trade. . . in 1865, he was employed as a marine engineer in the Vauxhall Foundry at Liverpool. . . .
. . . On the suggestion of the late Sir James Anderson, who was the commander of that ship, Mr. Gray's invention of the differential gear enabled the steering engine, when placed at a distance from the navigating station, to be controlled by the movement of the steering wheel, so that the helm could be made to follow and assume any desired position. The first trial of the Great Eastern gear was made in March, 1867, and was successful. . . .[more]