In 1739, Leonhard Euler solved the ordinary differential equation for a forced harmonic oscillator and noticed the resonance phenomenon. In 1742, Colin Maclaurin discovered his uniformly rotating self-gravitating spheroids. In 1742, Benjamin Robins published his New Principles in Gunnery, establishing the science of aerodynamics. British work, carried on by mathematicians such as Taylor and Maclaurin, fell behind Continental developments as the century progressed. Meanwhile, work flourished at scientific academies on the Continent, led by such mathematicians as Bernoulli and Euler, as well as Joseph-Louis Lagrange, Pierre-Simon Laplace, and Adrien-Marie Legendre. In 1743, Jean le Rond d'Alembert published his Traité de dynamique, in which he introduced the concept of generalized forces for accelerating systems and systems with constraints, and applied the new idea of virtual work to solve dynamical problem, now known as D'Alembert's principle, as a rival to Newton's second law of motion. In 1747, Pierre Louis Maupertuis applied minimum principles to mechanics. In 1759, Euler solved the partial differential equation for the vibration of a rectangular drum. In 1764, Euler examined the partial differential equation for the vibration of a circular drum and found one of the Bessel function solutions. In 1776, John Smeaton published a paper on experiments relating power, work, momentum and kinetic energy, and supporting the conservation of energy. In 1788, Lagrange presented his equations of motion in Mécanique analytique, in which the whole of mechanics was organized around the principle of virtual work. In 1789, Antoine Lavoisier stated the law of conservation of mass. The rational mechanics developed in the 18th century received expositions in both Lagrange's Mécanique analytique and Laplace's Traité de mécanique céleste (1799–1825).