C. Northcote Parkinson and journalist Ann Fry (1921–1983), with whom he had two sons and a daughter. In 1958, while still in Singapore, he published his most famous work, "Parkinson's Law", which expanded upon a humorous article that he had published in the "Economist" magazine in November 1955, satirising government bureaucracies. The 120-page book of short studies, published in the United States and then in Britain, was illustrated by Osbert Lancaster and became an instant best seller. It explained the inevitability of bureaucratic expansion, arguing that 'work expands to fill the time available for its completion'. Typical of his satire and cynical humour,
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