A thermometer is a useful aid used to measure body temperature. A thermometer is usually filled with mercury. Mercury in the tube rises when expanded by an increase in body temperature.
Review Date 9/22/2018
Updated by: Jatin M. Vyas, MD, PhD, Assistant Professor in Medicine, Harvard Medical School; Assistant in Medicine, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital, Boston, MA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.