is variously attributed to Cornelius Drebbel, Paul Sarpi, Galileo, and Sanctorio; though, we believe, the person first mentioned, deserves the credit of having invented the earliest thermoscope, in the year 1638, at Alkmaar, in North Holland. It was, however, an imperfect attempt; being regulated solely by the expansion of the air; and serving at the same time as a barometer; for his tube contained a mixture of water and aqua-fortis. Hence it was, in its primary state, called an air-thermometer; and, after substituting various other liquids, which were adopted by the Florentine Academy, by Sir Isaac Newton, and other philosophers, but which, on account of their uncertain properties, have long been disused, Dr. Halley proposed, in the year 1680, to employ quicksilver for this important purpose. Daniel Gabriel Fahrenheit, a native of Danzig, was the first who successfully availed himself of that suggestion, in 1709; when he produced his newly graduated tube, containing the mercurial fluid.—He ascertained the artificial freezing point in the same year, during the severe winter; by observing, that a mixture of snow and sal-ammoniac, uniformly caused spirit of wine to descend to the point marked, and no farther.—Hence, he was induced to denote such part of his cylindrical tube with 0 or zero: from this point to that of the usual temperature of the human body in a healthy state, he divided the intermediate space into 96 degrees; and thence to that of boiling water into 126°, so that the latter mark, in his scale, rises exactly to 212°. Thus, Fahrenheit claims not only the merit of having introduced the most scientific and convenient division of the thermometrical scale, but also that of adopting the mercurial fluid, which is doubtless the most proper, and perhaps the only one furnished by Nature, for measuring the various degrees of heat and cold, in the most accurate and sensible manner.—M. De Luc has proved, by conclusive arguments, the superiority of thermometers supplied with mercury, over those containing alkohol; and that the rising of the mercury, at all seasons, very nearly corresponds with the increase of heat. On the other hand, De Serviere remarked, that the column of mercury, in a perpendicular thermometer, tends to impede the accurate motion of this metallic fluid, on account of its own specific gravity: hence, he has judiciously proposed to remedy such defect, by keeping the instrument in a horizontal position.
M. De Reaumur, in 1730, proposed a new division of the thermometrical scale, by introducing 1000 parts of diluted spirits of wine into his tube with the usual globe, then commencing to count from 0 upwards, to the boiling point, which he marked with 80°. Such contrivance, however, having been found inconvenient for calculating the different degrees of heat and cold, with sufficient accuracy, Reaumur's globes, with their tubes, were subsequently also furnished with mercury; and are at present chiefly employed by the French, and in some parts of Germany.—To enable the reader to form a distinct idea of the difference subsisting between the two instruments, here described, we shall subjoin a comparative table of their scales.
