Electrical alarm thermometer having 4½” silvered and engraved dial, the register calibrated in degrees Fahrenheit and Centigrade with corresponding ranges from 30-170 & 0-80 divided to one degree. The upper part marked “Electrical Alarm Thermometer, Fahrenheit and Centig. Scale,” signed in the lower portion “Negretti & Zambra, London.” Blued steel pointer and glass mounted index. Helical bi-metallic sensor with ported housing, screw down electrical contacts, all contained in a brass drum form case, having case extension and suspension ring. Easel type stand to verso.
Condition: Generally good, the dial with some losses though remaining clear to read, a small mark showing as brass at approximately half past two position. This might have been the position of an electrical contact now missing – given a pattern this is replaceable. The index a replacement. The brass case retaining traces of original finish. The mechanical mechanism working and showing temperature change.
Comments: Large mechanical thermometers of this type have always been very unusual, the basic system one used extensively in thermographs. This instrument combines both electrical and mechanical systems, and would have required wiring to a power source and probably a bell or buzzer alerting the user to either a fall or rise in temperature beyond a particular value.
Research has been unable to show any similar instruments from this maker, though it should be noted that Negretti & Zambra produced many instruments combining mechanical sensors with electrical interpretation.
NB: Any electrical connection should be made professionally, and to a low voltage source. Not tested electrically.
A very attractive rare working instrument of some considerable interest.
Dimensions: 5” diameter x 2½” deep
Stock No: SI2062