Time changes most things, and physical constants are seem ingly not immune from this contingency. The publishers' suggestion for a new edition has provided an opportunity for a thorough scrutiny of the contents of this book and for the adjustment to some fourteen years of changes since the last edition. At the same time the contents have been increased by the addition of one or two new tables, and current moves towards the adoption of an international system of units ex plain the appearance in the book, wherever it is practicable, of S. 1. units. However, the habits of a lifetime are not...