A thermometer is an instrument for measuring temperature. Most antique thermometers consist of a sealed glass tube containing mercury or coloured alcohol, which expands and contracts with changes in temperature against a graduated scale. They were made as standalone instruments and were also incorporated into barometers, desk sets, clocks and garden and greenhouse fittings.
The mercury thermometer was developed by Daniel Gabriel Fahrenheit in the early eighteenth century, and the Fahrenheit scale became the standard in Britain for domestic instruments, with the Celsius scale used more widely on the Continent. Georgian and Victorian makers produced elegant wall thermometers with scales of silvered brass, ivory, bone or boxwood mounted on mahogany, oak or ebonised boards, and the maximum and minimum thermometer devised by James Six in the late eighteenth century was popular with gardeners and amateur meteorologists. Desk thermometers in brass, silver or marble frames, and novelty designs in the form of obelisks or columns, also survive in numbers. Collectors value signed scales, original tubes and good overall condition. Broken mercury tubes should be handled with great care, as mercury is toxic, and repair is best left to a specialist.
