Most people think of a thermometer as mercury in a glass tube, and indeed, since the normal range of temperatures we are likely to experience is extremely small, this is the kind in most general use. The clinical thermometer (top illustration) is a modified form of the normal mercury thermometer. Since the variation of body temperature is so small, certainly no more than 10 or 15 degrees (in Fahrenheit) around the average (98.4°F), it is graduated only within these limits. There is a narrowing in the tube just above the reservoir so that the level of mercury will not fall immediately the thermometer has been removed from the patient to be read.
The platinum resistance thermometer (bottom illustration) consists of a length of fine platinum wire wound on a mica frame and enclosed in a protective glass tube. Temperatures are found by measuring the wire's electrical resistance (this increases as it temperature rises).
Related entries• Beckmann thermometer
Related categories• HEAT AND THERMODYNAMICS
• LABORATORY EQUIPMENT
Home • About • Copyright © The Worlds of David Darling • Encyclopedia of Alternative Energy • Contact