electrical vacuum switch having two contact members carried by contact rods for moving the contact members in and out of engagement with each other , in which each contact rod is partly surrounded by a yoke of magnetic permeable material , closely adjacent each contact member , each yoke leaving a gap between the yoke legs , so that upon moving the contact members out of engagement , the magnetic flux lines , generated in each yoke by the current through the contact rods , will traverse the arcing gap between the contact members , towards the opposing yoke , resulting in a magnetic field in the arcing gap .