John Hays Hammond, mining engineer and businessman, graduated as a Bachelor of Philosophy (PhB) at the Sheffield Science School, Yale University, in 1876. He then went to Germany and qualified as a mining engineer at the Royal School of Mines at Freiburg in 1879. Returning to the United States he married Natalie Harris in 1881 and soon established himself as a well-known consulting engineer and mine valuer. During his career he examined mining properties in many parts of the world. He acted as a special expert to the United States Geological Survey, examining the California goldfields in 1880. Thereafter he worked as a consulting engineer to the Union Iron Works, San Francisco, and to the Central and Southern Pacific Railroads. In 1890 two reports by him were published by the California State Mining Bureau: "The auriferous gravels of California" and "Mining of gold ores in California".
Through the influence of Gardner F. Williams* Hammond met the financier Barney Barnato in 1893 and was appointed to manage Barnato Brothers' properties on the Witwatersrand. The appointment was for six months at a large salary. He arrived in Johannesburg later that year and in December became a member of the South African Association of Engineers and Architects, serving on its council during 1894/5. He resigned his post with the Barnato Brothers at the end of the brief contract period, partly because they did not act upon his advice to concentrate on mining at deep levels. Cecil John Rhodes, then Prime Minister of the Cape and managing director of Consolidated Goldfields of South Africa, next employed him as consulting engineer to both the British South Africa Company, which had mining rights in Rhodesia (now Zimbabwe), and Goldfields. He submitted his Report to the British South Africa Company on the mineral resources of Rhodesia in November 1894, and though it did not support the high hopes of shareholders, it aroused sufficient interest to stimulate the development of the territory. At this time he convinced Rhodes that mining at depth would be profitable and would secure the future of the gold mines - views he shared with men such as James S. Curtis* and Hennen Jennings*. Though Hammond's later claims to have originated deep level mining on the Witwatersrand were unfounded, he was the first to address the engineering problems involved. For example, he was instrumental in greatly increasing the speed of shaft sinking. Furthermore, in the preface he wrote for The gold mines of the Rand... (1895) by F.H. Hatch* and J.A. Chalmers*, he confidently stated that the gold-bearing strata of the Witwatersrand might be worked to a depth of 1500 meters.
Hammond supported the political views of the immigrant community. He was one of the original four members of the Reform Committee and played a role in planning the Jameson Raid, aimed at changing the government of the South African Republic. Following the abortive raid during the last few days of 1895 he was arrested and in April 1896 sentenced to death by the Transvaal High Court in Pretoria. However, the sentence was not carried out and after paying a substantial fine he was released in June 1896. He described these turbulent times in three publications: "South Africa and its future" (North American Review, 1897), The Transvaal trouble: an address by John Hays Hammond (New York, 1900), and years later, The truth about the Jameson Raid (New York, 1918).
After his release Hammond moved to London for a few years, though he visited South Africa several times to inspect mines of the Goldfields group. During 1898 he published two articles in the Engineering Magazine, one on "The diamond mines of South Africa", the other on "The gold mines of the Witwatersrand". In December 1899 he resigned his post and returned to the United States. He opened an office in New York, acted as consultant to various American mining and railway companies, and travelled extensively in the United States and Mexico to examine mines. At the same time he held an appointment as Professor of Mechanical Engineering at Yale University from 1902 to 1909, and served as president of the American Institute of Mining Engineers in 1907. It was on his advice that Goldfields of South Africa invested in mining, power and railway companies throughout the United States and Mexico. In 1902 he published a paper on "Gold mining in the Transvaal" in the Transactions of the American Institute of Mining Engineers. Later he began to devote more time to public affairs, but though he had political aspirations his political achievements were modest. In 1922 he was appointed chairman of the United States Coal Commission.
In his later years Hammond wrote books entitled The engineer (New York, 1921) and Great American issues, political, social, economic (New York, 1921). He was a brilliant engineer who played a significant role in the development of South Africa's gold mining industry. Several universities, including Yale, conferred honorary degrees upon him. He died of a heart attack in Gloucester (either in Maryland or in Virginia) and was buried in New York. The autobiography of John Hays Hammond was published in New York in 1935.