565,309. Signalling or controlling liquid levels. BRITISH THERMOSTAT CO., Ltd., and SHERLOCK, J. E. May 13, 1943, No. 7630. [Class 123 (i)] [Also in Group XXXVII] A casing 1, shown in sectional elevation, is connected by pipes 2 to a boiler, and is provided with thermally expansible metal tubes 4, 5 one above the other, fixed to the end wall 6. The opposite ends slide in a guide 7 fixed to the end wall 9, and each tube contains a push-rod 11, 12 of " Invar " (Registered Trade Mark), the free ends of which actuate an electric switch 25. The switch mechanism comprises a rocking lever 19 pivoted at 20, surrounding a fixed member 31 and integral with arms 21, 22 engaged by the rods 11, 12. The free ends of arms 22 carry adjustable elements 23 for operating a rod 24 which controls the switch 25 mounted on a fixed bracket 26. The pivot 20 is carried by a sliding member 27 which is pressed by spring 28 to maintain the arms 22 in engagement with rods 11, 12. The tube 5 is constantly subject to an electric heater 10, but approximates in temperature to tube 4 so long as it is submerged. If uncovered by a fall of water level, tube 5 rises in temperature and actuates its rod 12 to move the switch rod 24. Variations in ambient temperature of the rods 4, 5 do not operate the switch. The switch controls a pump, valve, or alarm device.