Wea (TM)ve all heard of Newton's bucket, Einstein's elevator, and SchrAdinger's cat - these are some of the best known examples of thought experiments in the natural sciences. But what function do these experiments perform? Are they really experiments at all? Can they help us gain a greater understanding of the natural world, or are they merely illustrations of one or another argument about the way things work? In this revised and updated new edition of his classic text, The Laboratory of the Mind, James Robert Brown continues to defend apriorism in the physical world, including a new chapter on the role of intuition in thought experiments, and new material on thought experiments in mathematics. With plenty of illustrations, and updated coverage of the debate between rational platonism and classic empiricism, this is a lively and edifying contribution to the field of philosophy of science.