Mercury switches
Mercury switches were used in several Tektronix products for generating pulses with clean edges. The switches are electromagnetic relays with mercury-wetted contacts inside glass envelopes that contain pressurized gas. The gas prevents arcing of the contacts. Mercury switches have limited life. In pulse generators, the coil of the relay is typically driven by a multivibrator or other periodic current source. Turning off the coil drive waveform when the pulse generator is not in use is recommended.
Tektronix products using mercury switches are: