Page:Evolution of the thermometer.djvu/49

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48
EVOLUTION OF THE THERMOMETER.

Guericke's thermomet'r.

so as to form a very narrow U, in which was placed a certain amount of alcohol. The shorter arm of the U was open at the top; on the liquid within it floated a tiny inverted cup of brass foil to which a cord was attached that passed around a wheel, hung upon the underside of the globe, and carried at the other end a little figure of an angel pointing to the scale on the tube; the tube was concealed from the observer by a wooden case, and the image hung without. A valve at one side of the large copper sphere permitted enough air to be withdrawn by means of the air-pump, to adjust the height of the image, which hung about half way up the tube. On the fifteen-foot scale were the words: "Magum frigus, aer frigidus, aer subfrigidus, aer temperatus, aer subcalidus,