and proved, in 1872, using the "-function," that the Maxwellian distribution is stable and any non-Maxwellian distribution would morph into it. In his Dynamics of Rigid Bodies (1877), Edward John Routh noted the importance of what he called "absent coordinates," also known as cyclic coordinates or ignorable coordinates (following the terminology of E. T. Whittaker). Such coordinates are associated with conserved momenta and as such are useful in problem solving. Routh also devised a new method for solving problems in mechanics. Although Routh's procedure does not add any new insights, it allows for more systematic and convenient analysis, especially in problems with many degrees of freedom and at least some cyclic coordinates. In 1899, at the request the British Association for the Advancement of Science from the year before, Edmund Taylor Whittaker submitted his Report on the Progress of Solution to the Problem of Three Bodies. At that time, classical mechanics in general and the three-body problem in particular captured the imagination of many talented mathematicians, whose contributions Whittaker covered in his Report. Whittaker later incorporated the Report into his textbook titled Analytical Dynamics of Particles and Rigid Bodies (first edition 1907). It helped provide the scientific basis for the aerospace industry in the twentieth century. Despite its age, it remains in print in the early twenty-first century. Thermodynamics, heat engines, and refrigerators During the 1830s and 1840s, traditional caloric theory of heat began losing favour to "dynamical" alternatives, which posit that heat is a kind of motion. Brewer and amateur scientist James Prescott Joule was one of the proponents of the latter. Joule's intricate experiments—the most successful of which involved heating water with paddle wheels—making full use of his skill in temperature control as a brewer, demonstrated decisively the reality of the "mechanical equivalent of heat." What would later become known as the "conservation of energy" was pursued by many other workers approaching the subject from a variety of backgrounds, from medicine and physiology to physics and engineering. Another notable contributor to this development was the German researcher Hermann von Helmholtz, who gave an essentially Newtonian, that is, mechanical, account. William Thomson (later Lord Kelvin) received the works of Joule and Helmholtz positively, embracing them as providing support for the emerging "science of energy." In the late 1840s to the 1850s, Kelvin, his friend William John Macquorn Rankine, and the German Rudolf Clausius published a steady stream of papers