mercury-wetted reed switch

mercury-wetted reed switch

[′mər·kyə·rē ¦wed·əd ′rēd ‚swich]
(electricity)
A reed switch containing a pool of mercury at one end and normally operated vertically; the contacts on the reeds are covered with a mercury film by capillary action; each operation of the switch renews this mercury film contact, thereby increasing the operating life of the switch many times.