TYNDALL, tin'dal, JOHN ( 1820-93), An English physicist, born at Leighliu Bridge, Coun ty Carlow, Ireland. He found employment at first in one of the subordinate grades of the Ord no nee Survey, and later as a railroad engineer. He was appointed teacher of mathematics and surveying at Queenwood College. Stockbridge, in 1847. He then went to Marburg. where he stud ied for two years, returning to Queenwood in 185I. In January. 1853, Tyndall communicated his first paper to the Royal Society, On. Molecular Influences—Transmission of Heat Through Or ganic Structures. In the following month a lec ture On the Influence of Material Aggregation upon the Manifestations of Force, before the Royal Institution, widely extended his fame, and inaugurated his reputation as a brilliant lecturer. A few months later he was appointed professor of natural philosophy in the Royal Institution, thus becoming a colleague of Faraday, succeed ing as director on the latier's death in 1867. Tyn dall early undertook researches on diamagnetism at Marburg in conjunction with Knoblauch, which resulted in a publication entitled On the Magneto-optic Properties of Crystals and the Re lation of Magnetism and Diamagnetism to Molee vlar Arrangement. These and later researches were published under the title of Researches on Diamagnetism and Magno-crysta11ic Action, In cluding the Question. of Diamagnetic Polarity (1870). Tyndall spent much time in the Alps. where he combined mountain-climbing with scien tific research, making numerous careful observa tions on the great Swiss glaciers. These were published in popular form and in scientific con tributions to the Philosophical Transactions. In connection with his study of the glaciers, Tyn dall became interested in atmospheric phenomena, particularly the study of vapors. This led to researches on radiant heat and its transmis sion, radiation, and absorption by vapors and gases. These investigations involved a contro versy with :Magnus, but Tyndall was able to de monstrate the correctness of his views. These
researches were later collected and published un der the title Contributions to Molecular Physics in the Domain of Radiant Reat (1872). In his study of radiant energy Tyndall analyzed various kinds of light in order to determine the proportion of luminous and non-luminous rays and their effect on various substances. He also discovered that in 'optically pure air.' that is. air free from dust or other particles, a luminous beam is in visible. These discoveries led to improved meth ods of sterilization, which are described in his Essays on Floating Matter of the Air in Relation to Putrefaction and Infection.
The British Government availed itself of Tyn dall's.seientifie ability and he succeeded Faraday as a scientific adviser to Trinity Ilouse (in charge of the lighthouse service) and the Board of Trade, in which capacity he carried on a num ber of scientific experiments with direct practical ends. Tyndall also achieved a reputation as a lecturer and did much valuable work in the pop ularizing of science. Few scientific lecturers have been able to present. the principles and facts of physics to the general public so successfully as Tyndall. He visited the United States in 1872 73, on a lecture tour, and a few years after he gave the proceeds to forward the cause of original research in the United States. He wrote many popular treatises on scientific subjects, which have been translated into foreign lan guages. Among his works are: Fleat Considered as a Mode of Motion (1S63 and subsequent edi tions) ; On Sound (1867 and subsequent edi tions) ; Fragments of Science for Unscientific People (1871 and subsequent editions) ; Six Lec tures on Light Delivered in America in 1872-3 (1873 and layer editions) ; New Fragments (1892 and 1897) ; Notes on Light (1870) ; Sotes on Electrical Phenomena. and Theories (1870). Ms works on the glaciers and the Alps inehule The Glaciers of the Alps ( 1860 and 1896) ; Mountain eering in 1861 (1S62) ; and flours of Exercise in the Alps (1871 and later editions).