Thomas Reid was an intellectual polymath whose interests encompassed all aspects of Enlightenment thought. Paul Wood reconstructs for the first time Reid's career as a mathematician and natural philosopher and shows how he grappled with various aspects of the scientific legacy of Sir Isaac Newton. This book provides the drafts and printed text of his earliest publication, 'An Essay on Quantity', along with a selection of his mathematical papers, including the significant series of manuscripts dealing with Euclid's problematic parallels postulate. Other manuscripts illustrate his skill as an observational astronomer, his work in optics dealing with the aberration of light, his speculations on electricity, and his engagement with the revolutionary chemical system of Lavoisier. Read in conjunction with Thomas Reid on the Animate Creation, this volume shows why Reid's contemporaries regarded him as an accomplished man of science.