Circuit breakers, relays, terminals, microphones, current collectors and commutators, all operate with electric contacts. Industry is making extensive use of contacts with ever-increasing demands on efficiency. The need of up to date reliable theories as well as of formulas and tables for applications is becoming pressing. This book is an attempt to meet this need. As is the case in many other branches of technology today, problems which arise in the field" of electric contacts involve insight in various other disciplines of physics, including parts which have not yet developed to such an extent that they. are treated in elementary text books. Con­ sidering the lack