GEISSLER, Heinrich (1814-79), a distinguished practical physicist, was born at the village of Igelshieb in Saxe-Meiningen, Germany, where he was educated as a glass-blower. After many years spent in travelling from city to city in the exercise of his craft, he settled at Bonn, where he speedily gained a high reputation, not only for his surpassing skill and ingenuity of conception in the fabrication of physical apparatus, but for his comprehensive knowledge, acquired chiefly in later life, of the natural sciences. With Pliicker, in 1852, by means of an ingeniously contrived instrument, in which mercury was made to compensate for the expansion of the glass, he ascertained the maximum density of water to be at 3 ’ 8° C. He also determined the coefficient of expansion for ice between - 24° and - 7°, and for water freezing at 0°. In 1869, in conjunction with Vogelsang, he proved the existence of liquid carbon dioxide in cavities in quartz and topaz, and later he obtained amorphous from ordinary phosphorus by means of the electric current. He is best known as the inventor of the sealed glass tubes which bear his name, by means of which are exhibited the phenomena accompanying the discharge of electricity through highly rarefied vapours and gases (see Electricity, vol. viii. p. 64). Among other apparatus contrived by him are his vaporimeter, mercury air-pump, balances, normal thermometer, and areometer. From the university of Bonn, on the occasion of its jubilee, he received the honorary degree of doctor of philosophy. He died on the 24th of January 1879, in the sixty-fifth year of his age. See A. W. Hofmann, Βer. d. deut, chem. Ges., 1879, p. 148.