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Christian Otto Mohr was an engineer whose work connected graphical methods with the analysis of stressed materials. Mohr's circle represents the normal stress and shear stress on differently oriented planes by points on a circle, turning a change of coordinates into a geometric construction. TU Dresden's historical account relates this construction to his 1882 work on the representation of stress and deformation.^[ref]

For a two-dimensional stress tensor, the circle has centre $({\sigma }_x+{\sigma }_y)/2$ and radiusIts horizontal intercepts give the principal stresses. This makes Mohr's circle useful for seeing both extremal stresses and the relation between plane orientation and the components of stress.

An engineer develops or evaluates a design against practical requirements using engineering methods. The reasoning includes the intended function, the conditions under which it must work, the approximations in its model and the evidence supplied by tests or measurements. For a small actuator, force capacity, response time, heating and manufacturing tolerances can all matter. Different specializations select different tools, but the common task is to justify how a constructed system will meet its specified function.

An engineer who developed laser instrumentation at Laboratoire Charles Fabry.^[ref]

Henry Bessemer was an engineer associated with the Bessemer process, a method for converting molten pig iron toward steel using an air blast. His 1856 patent describes introducing air into molten iron so that reactions within the bath generate heat while changing its chemical composition.^[ref]

The important design insight is the coupling between chemical reaction, mixing and heating: the unwanted constituents become part of the source of energy for processing the material. The Bessemer process consequently illustrates how understanding a material's chemistry can change the scale and speed of manufacture. Obtaining a desired steel still requires control of the starting chemical composition and the final carbon content.

Identity and portraits: National Portrait Gallery, sitter biography and dated portraits.

Ludwig A. Colding was a Danish engineer who investigated the conversion between mechanical work and heat as part of the nineteenth-century development of conservation of energy. His work connects a practical measurement question—how much heat accompanies an expenditure of mechanical work—with a general statement about the persistence of energy through changes of form.

In an English letter dated November 1863 and published in 1864, he traced his claim to the conservation principle back to his 1843 work. The letter is a useful primary source for what Ludwig A. Colding himself understood his contribution to be, including the importance he attached to experimental evidence. The historical use of the word force in this discussion should be read in context rather than identified automatically with the modern force.^[ref]

Vannevar Bush was an American engineer and science administrator whose 1945 report Science, the Endless Frontier by Vannevar Bush argued for sustained support of basic research and scientific training. He distinguished research aimed at general understanding from work directed toward a particular practical result, while stressing that the two activities depend on each other.

His argument concerned uncertainty as well as usefulness: the practical results of any one investigation cannot be predicted reliably, yet a continuing supply of new knowledge makes later technological development possible. He therefore proposed support for researchers and institutions rather than judging every investigation solely by an immediate product. The report links the organization of scientific work to the long-term development of engineering.^[ref]

W. J. M. Rankine was a Scottish engineer and physicist who contributed to thermodynamics, classical mechanics and the teaching of engineering. As professor of civil engineering and mechanics at Glasgow from 1855 to 1872, he emphasized connecting theory with practice and worked with shipbuilders on vessels and engines.^[ref]

The Rankine cycle connects his name with the analysis of heat engines using a working fluid that undergoes vaporization and condensation. Its idealized sequence of pumping, heating, expansion and cooling connects a practical steam engine to a calculation of mechanical work and thermal efficiency. The broader importance of his work lies in making quantitative physical theory part of systematic engineering design.

Institutional historical profile: Imperial College historical plaque booklet: William John Macquorn Rankine.