The spreading and interface resistances of electric contacts

In almost every electric circuit there axe one or more places where current passes from one continuous metal body to another across the interface separating the two. The presence of the interface introduces an additional resistance into the circuit, and this additional resistance has for many years been called contact resistance. For over a century the contact resistance was thought to arise entirely from the potential drop through which charge must pass in going across the interface from one body to the other, and this was considered to be the only resistance of a contact. Today, it is known that the deviation from a uniform current field caused by the constriction of the current to a few small conducting areas at the interface also contributes to the contact resistance. A recent paper1 by one of the authors describes some of the more important effects of this latter phenomenon.