1. A MERCURY BUTTON SWITCH COMPRISING: A METAL SHELL WITH A CLOSED TERMINAL END AND AN OPEN END, SAID METAL SHELL HAVING AN AXIS OF ROTATION THROUGH THE CLOSED TERMINAL END AND OPEN END THEREOF; AN ASSEMBLY HERMETICALLY SEALED TO THE OPEN END OF SAID SHELL, SAID ASSEMBLY CONSISTING OF A RETAINING RING AND CENTRAL TERMINAL PIN POSITIONED BY A VITREOUS INSULTING MEMBER IN THE ANNULAR SPACE THEREBETWEEN, AND A CERAMIC BARRIER DIRECTLY BONDED TO SAID INSULATING MEMBER, THE BOND BEING IMPERVIOUS TO LIQUID MERCURY AND MERCURY VAPOR; AND A QUANTITY OF MERCURY MOVABLE WITHIN SAID CERAMIC BARRIER TO MAKE ELECTRICAL CONTACT BETWEEN SAID SHELL AND SAID CENTRAL TERMINAL PIN.