Page:Popular Science Monthly Volume 52.djvu/708

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HE thermometer, the Abbé Nollet writes, came for the first time from the hands of a peasant of North Holland. This peasant, whose name was Drebbel, was not, however, in fact, one of those coarse fellows who know of nothing but field work; he seems to have been of a diligent nature, and had apparently some knowledge of the physics of the time. An ingenious inventor as well as an impudent pretender, and boasting that he had discovered perpetual motion, while he made great advances in the art of dyeing cloths, he secured favors from James I; Rodolf II gave him liberal pensions and brought him to his court; and Ferdinand II, who was himself interested in the thermometer, chose him as the tutor for his son.

Drebbel's thermometer—an invention which he may have borrowed from Porta, and in which Galileo doubtless preceded him—was composed of a vertical glass tube ending at the top in a bulb, while the lower end was plunged into a vessel filled with water or some colored liquid. When the bulb was warmed, a part of the air contained within it was driven back into the water and escaped without. When the air became cool again as the temperature around it, the external pressure caused the liquid to rise in the tube, the limit of its ascent being determined by the degree to which the air in the bulb had been heated, and the tension it had acquired.

This hardly practical apparatus was still used in Germany as late as 1621. The members of the Accademia del Cimento, with their active interest in all physical progress, soon substituted for it the more convenient instrument which we still use. Contained in a transparent bulb prolonged into a fine tube, a liquid more dilatable than the bulb rose in the tube when it was warmed, and descended when it was cooled. The Florentine Academy, moreover, never let any physical discovery pass without trying to apply it to the healing art. Galileo had hardly recognized the constancy of the time of the oscillations of the pendulum before the pendulum was used to determine the rapidity or the slowness of the pulses of patients. The thermometer, made convenient and portable, became in the hands of the Venetian physiologist Santorio Santori a sensitive and precise indicator of the progress of fever. Santori's writings made the instrument popular, and it was soon common in the enamelers' shops as the Florence or Sanctorius thermometer.

It is hard to imagine the interest that was excited by the indications of this instrument, which was declared to be "worthy of