Ministry of Defence Main Building (United Kingdom) each and cost £12,600. Similar figures representing "air" and "fire" were intended to be installed at the south end of the building, however these were never constructed. During the 1950s, building staff nicknamed the statues "Mr and Mrs Parkinson", after Cyril Northcote Parkinson, the Board of Trade civil servant who devised Parkinson's Law which states "work expands so as to fill the time available for its completion". More recently MOD staff refer to the statues as the "two fat ladies". The badge of the RAF is carved into stone columns either side of the southern entrance to the building, reflecting
Virtual work statics. Working with Leibnizian concepts, Johann Bernoulli systematized the virtual work principle and made explicit the concept of infinitesimal displacement. He was able to solve problems for both rigid bodies as well as fluids. Bernoulli's version of virtual work law appeared in his letter to Pierre Varignon in 1715, which was later published in Varignon's second volume of "Nouvelle mécanique ou Statique" in 1725. This formulation of the principle is today known as the principle of virtual velocities and is commonly considered as the prototype of the contemporary virtual work principles. In 1743 D'Alembert published his "Traité de Dynamique" where