I'm working on a Storage Display and

Physticaly, either a metal can about 2.5" * 0.75" * 0.5" to mount on a PCB or a larger cylindrical can about 4" tall with an octal plug on the bottom end/ Electrically, theyr'e a murcury-wetted reed cotnact with permanent magnets to bias it (induce a magnetic olarity i nthe reed) and one or more coils around it. They are stable in both states, a currnet through te coil one way will flip the contacts one way, a current thtough the coil the other way will flip the contacts the other way. They were used on 'double curent' telegraph lines where, say, +80V is a mark and -80V is a space. They were typically good to about 200baud, and had minimal distortion (the switching time and operating current in the 2 directiosn was the same). There were, of course, non-merucry polarised relays, Carpenter, Creed and WE being the ones I've either come across or read about. But the mercury-wetted ones were generally lower distortion and faster switching. -tony