Autograph Letter Signed ‘W.Froude’, to J.B.Macaulay, thanking him for the copy of the Admiral’s memo [Admiral Moorsom], discussing British Association Committee business, knowing now “how essential some new line of thought was as the old model would not fit in with facts”. 1 page 8 x 5 inches, in good condition. With the remains of the envelope, and a newspaper obituary of Froude (Times 7 June 1879). Torquay, 6 January 1878. Uncommon. William Froude (1810 – 1879 in Simonstown, South Africa), English engineer, hydrodynamicist and naval architect. He was the first to formulate reliable laws for the resistance that water offers to ships (such as the hull speed equation) and for predicting their stability. At Brunel’s invitation Froude turned his attention to the stability of ships in a seaway and his 1861 paper to the Institution of Naval Architects became influential in ship design. This led to a commission to identify the most efficient hull shape, which he was able to fulfil by reference to scale models: he established a formula (now known as the Froude number) by which the results of small-scale tests could be used to predict the behaviour of full-sized hulls.