among physicists. Scientific problems thus became the impetus for the development of the subject. William Rowan Hamilton advanced it in his course to construct a deductive framework for optics; he then applied the same ideas to mechanics. With an appropriate variational principle, one could deduce the equations of motion for a given mechanical or optical system. Soon, scientists worked out the variational principles for the theory of elasticity, electromagnetism, and fluid mechanics (and, in the future, relativity and quantum theory). Whilst variational principles did not necessarily provide a simpler way to solve problems, they were of interest for philosophical or aesthetic reasons, though scientists at this time were not as motivated by religion in their work as their predecessors. Hamilton's work in physics was great achievement; he was able to provide a unifying mathematical framework for wave propagation and particle motion. In light of this description, it becomes clear why the wave and corpuscle theories of light were equally able to account for the phenomena of reflection and refraction. Hamilton's equations also proved useful in calculating planetary orbits. In 1845, John James Waterson submitted to the Royal Society a paper on the kinetic theory of gases that included a statement of the equipartition theorem and a calculation of the ratio of the specific heats of gases. Although the paper was read before the Society and its abstract published, Waterson's paper faced antipathy. At this time, the kinetic theory of gases was considered highly speculative as it was based on the then not-accepted atomic hypothesis. But by the mid-1850s, interest was revived. In the 1860s, James Clerk Maxwell published a series of papers on the subject. Unlike those of his predecessors, who were only using averages, Maxwell's papers were explicitly statistical in nature. He proposed that the speeds of molecules in a gas followed a distribution. Although the speeds would cluster around the average, some molecules were moving faster or slower than this average. He showed that this distribution is a function of temperature and mathematically described various properties of gases, such as diffusion and viscosity. He predicted, surprisingly, that the viscosity of a gas is independent of its density. This was verified at once by a series of experiments Maxwell conducted with his wife, Katherine. Experimental verification of the Maxwell distribution was not obtained till 60 years later, however. In the meantime, the Austrian Ludwig Boltzmann developed Maxwell's statistics further