The S104/1k is a thermal delay switch. From the application of the heater power the bi-metalic strip will heat sufficiently to bend and make contact with the static electrode in 25 to 35 seconds.
Application are in providing a delay in the application of anode volts to mercury vapour rectifiers - thus giving a suitable time for the rectifier to be hot enough to operate. The data-sheet suggests that the delay switch be used to operate a latching relay that does the actual HT switching.
The heater runs through a ceramic tube. The static electrode is on the left.
The rear of the static electrode.
The heater is coiled within the ceramic tube.
The thin glass tube envelope is 18 mm in diameter, and excluding the B7G base pins is 44 mm tall.
References: Datasheet, 1040 & 1043. Type S104/1K was first introduced in 1958.