Curiosa Mathematica

This edition has been fully restored with modern typesetting, custom cover design. Charles L. Dodgson's fourth edition of Pillow-Problems opens with a strikingly personal preface: a mathematician's record of puzzles first worked out in wakeful hours, often in the night, and set down in the same form in which they were originally conceived. He explains the title change, defends the symbols he invented for convenience, and insists that these problems were meant less as a display of brilliance than as a practical refuge for an anxious mind. In a thoughtful meditation on attention and psychology, he argues that purposeful mental work can drive away worry, doubt, and darker intrusions by leaving them no room to grow. He also reflects candidly on the difficulty of preserving genuine mental solutions on paper, thanks a colleague for checking proofs, and adds a corollary on the conditions under which a tetrahedron is possible. The book then unfolds into a rich sequence of inventive mathematical problems and solutions in geometry, algebra, trigonometry, calculus, number theory, combinatorics, and probability. Triangles, circles, squares, parallelograms, tetrahedra, counters, bags, coins, and even business and motion puzzles all appear, inviting readers into a world of exact reasoning, elegant constructions, and surprising deductions. The collection rewards persistence with clear answers, hidden ratios, and memorable challenges that turn ordinary calculation into a lively exercise in ingenuity.