Synthesizes Welsh history of science during the long eighteenth century. '" World of New Ideas": 1650-1820 is a series of two volumes revealing the often-forgotten contributions made by Welsh scientists to the scientific history of the long eighteenth century. The first volume--The Isles--centers on the contribution made in Wales particularly but also includes England, Scotland, and Ireland. By presenting a synthesis of published material and original research in three sections (Theory, Practice, and Results), its chapters examine how Welsh contributions fit into the history of science developed from the quasi-magical worlds of alchemy and early chemistry, through the advent of Cartesian and Newtonian science, to the world of technological innovation and industrial development.