# Dictionary of National Biography, 1927 supplement/Reynolds, Osborne

​REYNOLDS, OSBORNE (1842–1912), engineer and physicist, was born 23 August 1842 at Belfast. He came of a clerical family. His grandfather and great-grandfather had been rectors of Debach-with-Boulge, Suffolk. His father, the Rev. Osborne Reynolds, was fourth wrangler in 1837, and subsequently fellow of Queens' College, Cambridge, principal of a school in Belfast, head master of Dedham grammar school, Essex, and finally, in his turn, rector of Debach. His mother was Jane Hickman. For his early education Reynolds, who was a boy at Dedham school, was indebted mainly to his father. He inherited a keen interest in mechanics, and at the age of nineteen entered the workshop of a mechanical engineer in order to make himself acquainted with the practical side of the subject before proceeding to Queens' College, Cambridge. He graduated in 1867 as seventh wrangler, and was elected a fellow of Queens' in the same year. After a short period in the office of a civil engineer, he was appointed in 1868 to the newly instituted professorship of engineering in the Owens College, Manchester. This post he held until his retirement, through ill-health, in 1905.
The courses of study laid down by Reynolds as professor were somewhat exacting, but he succeeded in rousing the interest and even enthusiasm of the more capable among his students, many of whom afterwards came to occupy posts of distinction. His long tenure of the professorship is chiefly memorable, however, for the series of original investigations which he carried out, sometimes with the co-operation of his assistants and pupils, to whom he always assigned a generous share of credit. These investigations dealt almost entirely with mechanical questions, or with physical phenomena so far as they appeared to admit of a mechanical explanation, and were highly original both in conception and in execution. Reynolds's acute physical insight enabled him to explain phenomena which other minds had regarded as obscure or even paradoxical. ​Examples of this are his work on lubrication, which has led to important practical inventions; on the laws of the flow of water in pipes, with the recognition of the ‘critical velocity’, now universally known by his name, at which the flow changes its character; and on the ‘dilatancy’, as he called it, of granular media. The same peculiar insight is shown in his papers on atmospheric refraction of sound, and on the ‘group-velocity’ of water waves, where, in both cases, he made important additions to the work of Sir George Gabriel Stokes [q.v.].
Although Reynolds made valuable contributions to engineering practice, as in the design of turbine pumps, and in the study of the laws of communication of heat from a metal surface to a fluid, his scientific reputation will probably rest mainly on his work in general physics, although this, it may be said, was suggested often by some practical question of engineering. The most extensive piece of experimental work which he carried out was a determination of the mechanical equivalent of heat from a novel point of view. The object here was the direct measurement of the amount of heat required to raise a pound of water from the freezing to the boiling point, the result being thus independent of the thermometric properties of any particular substance, such as mercury or glass. This must always rank as a classical instance of the determination of a physical constant.
The scientific papers of Reynolds were published in a collected form, Papers on Mechanical and Physical Subjects, in three volumes (1900–1903). Of their originality and value there is no question, but it cannot be said that they are always easy to follow. The leading idea is in most cases simple; indeed, Reynolds's bias was always to look for a simple explanation, rather than for one which depended on the concurrence of a number of independent causes. But the involved style of exposition which he adopted had a tendency to perplex all but determined students, with the result that much of his work, especially his theoretical work, was long in gaining general acceptance. By his scientific compeers his worth was early recognized. He was elected a fellow of the Royal Society in 1877, and was awarded its gold medal in 1888.
The character of Reynolds was, like his writings, strongly individual. Somewhat reserved in serious or personal matters, and occasionally combative and tenacious in matters of university politics, he was kindly and generous in all ordinary relations of life. He had a keen sense of humour, and delighted in starting paradoxes, which he would maintain, half seriously and half playfully, with great ingenuity and resource. After his retirement (1905) he lived at St. Decuman's, Somerset, where he died 21 February 1912. An admirable portrait by the Hon. John Collier hangs in the hall of Manchester University.
Reynolds married twice: first, in 1868 Charlotte (died 1869), daughter of Dr. Chadwick, of Leeds; secondly, in 1881 Annie Charlotte, daughter of the Rev. Henry Wilkinson, rector of Otley, Suffolk. By his second marriage he left three sons and a daughter.
[Proceedings of the Royal Society, vol. lxxxviii, A, 1912–1913; private information; personal knowledge.]
H. L.