In 1867, Sir William Thomson (later Lord Kelvin) and Peter Guthrie Tate revolutionised physics with the publication of their Treatise on Natural Philosophy, in which they demonstrated the centrality of energy conservation to systems of dynamic movement. Popularly known as 'T&T' for its authors' initials, the Treatise became the standard textbook on natural philosophy, introducing generations of mathematicians to the 'new energy-based dynamics'. In Elements of Natural Philosophy (1873), they distil the portions of the Treatise not requiring higher calculus into a primer suitable for use in university courses. The first half covers the basic principles of kinematics and dynamics, including the motion of points, lines, and volumes, while the second half concerns questions of 'abstract dynamics', including particle attraction. The result of one of the most important collaborations in modern physics, this book remains a thorough introduction to the major principles of Thomson and Tait's larger work.