In this groundbreaking two-volume textbook, presented here in one volume and first published in 1867, Lord Kelvin and Peter Guthrie Tait offer a unified scientific explanation of the physical world through the laws of energy. They defined much of what today is considered physics, covering such realms as liquid motion, instantaneous velocity, and the motion of a rigid body around a fixed point. From simple movement to fluid dynamics, the authors provide readers with the necessary science and mathematics to describe complex systems of motion. Irish scientist, engineer, and author LORD WILLIAM THOMSON KELVIN (1824-1907) is considered a foundational thinker of modern physics. He invented the Kelvin temperature scale and also helped develop the first transatlantic telegraph cable. Scottish physicist PETER GUTHRIE TAIT (1831-1901) was educated at Cambridge. Among his writings is the scientific and religious text The Unseen Universe (1901).