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, and salubrity of the air in different places, cultivated fields, plains or mountains, as well as the temperature of man in disease. He mentions a thermoscope containing mercury, but does not describe its construction; the text is accompanied by the figure of a thermoscope of which the stem is twisted into a spiral several feet in length. No reference is made to a scale. (Magnes, 1643, p. 515).

John Baptist van Helmont, a physician and chemist of Brussels, used in 1648 an air-thermometer similar in design to that of Leurechon, except that the stem had only a large drop of water, as in that of Mersenne. (Opera, 1648, p. 64.)

A most important and radical improvement in thermometers was made some time prior to 1654, by Ferdinand II, Grand duke of Tuscany, the liberal patron of literature and art, who devoted himself also to practical researches in physical science. Ferdinand made a thermometer of the usual form, filled it to a certain height with colored alcohol and then sealed it hermetically by melting the glass tip ; the