Sir James Alfred Ewing KCB FRS FRSE DL[1] MInstitCE (27 March 1855 − 7 January 1935) was a Scottish physicist and engineer, best known for his work on the magnetic properties of metals and, in particular, for his discovery of, and coinage of the word, hysteresis.

During his summer vacations, he worked on telegraph cable laying expeditions, including one to Brazil, under William Thomson, 1st Baron Kelvin and Fleeming Jenkin.

Ewing made two special friends at Tokyo University soon after arriving: Basil Hall Chamberlain and Lieutenant Thomas Henry James RN, who taught navigation.

He was also in close contact with Henry Dyer and William Edward Ayrton at the Imperial College of Engineering (Kobu Dai Gakkō).

His investigations into earthquakes led him to help develop the first modern seismograph, alongside Thomas Gray and John Milne of the Imperial College of Engineering, from 1880 to 1895.

[citation needed] Ewing also researched into the crystalline structure of metals and, in 1903, was the first to propose that fatigue failures originated in microscopic defects or slip bands in materials.

[citation needed] In 1898, Ewing took his wife and children to Switzerland for a mountaineering holiday with the family of noted Professor of Electrical Engineering at King's College, John Hopkinson.

[citation needed] On 8 April 1903, The Times announced that the Board of Admiralty selected Ewing for the newly created post of Director of Naval Education (DNE) in Greenwich.

Ewing's first wife, Annie (née Washington) died in 1909 and, in 1912, he married Ellen, the surviving daughter of his old friend and patron, John Hopkinson.

[12] During World War I, from 1914 to May 1917, Ewing managed Room 40, the Admiralty intelligence department of cryptanalysis, responsible predominantly for the decryption of intercepted German naval messages.

In this capacity, he achieved considerable fame in the popular press when Room 40 deciphered the Zimmermann Telegram in 1917 (which suggested a German plot to assist Mexico in recovering the southwestern United States).

In May 1916 Ewing accepted an invitation to become Principal of the University of Edinburgh, in the course of which he instituted an extensive series of effective reforms and which he held until his retirement in 1929.