Also 7 -tre. [mod. f. Gr. θέρμ-η heat, θερμό-s hot + μέτρον measure: see -METER. In F. thermomètre (1624).
The name thermoscopium appears somewhat earlier: see THERMOSCOPE.]
An instrument for measuring temperature (see TEMPERATURE 7) by means of a substance whose expansion and contraction under different degrees of heat and cold are capable of accurate measurement.
For the history of the instrument and its names, see H. C. Bolton, The Evolution of the Thermometer (Easton Pa., 1900), Renou, Hist. du Thermomètre (Versailles, 1876), Burckhardt, Zur Geschichte des Thermometers, 1902.
The earliest form was an air-thermometer invented and used by Galilei a. 1597, for indicating the temperature of the atmosphere; alcohol thermometers were used c. 1650; the device of a fixed zero (orig. the freezing-point) was introduced by Hooke, 1665. The fixing of the zero at an arbitrary point below the freezing point is attributed to FAHRENHEIT of Amsterdam, who made mercurial thermometers c. 1720, and his scale has been in general use in England since c. 1724. The zero of REAUMUR (1730), and of the CENTIGRADE thermometer of Celsius (1742), now largely used in science, is (like that used by Hooke and Sir I. Newton) the freezing-point. The ordinary form is now a slender hermetically sealed glass tube with a fine bore, having a bulb at the lower end filled with mercury, or with alcohol or other liquid, and adjusted to a graduated scale; variations of temperature being indicated by the varying heights of the column of liquid in the tube, due to its expansion and contraction.
Air-, Centigrade, Clinical, Differential, Fahrenheit, Gas-, Maximum-, Minimum-, Réaumur, Register thermometer: see the first elements. Metallic (or bimetallic) thermometer, a thermometer which indicates temperature by differential expansion and contraction of composite metal bars.
[1624. ‘H. van Etten’ (J. Leuréchon), Récréation mathématique (1626), 99. Thermomètre ou instrument pour mésurer les degrez de chalour ou de froidure qui sont en l’air.]
1633. W. Oughtred, trans. van Etter’s Math. Recr., 110. Of the Thermometer: or an instrument to measure the degrees of heat and cold in the aire.
1646. Sir T. Browne, Pseud. Ep., 227. The same is evident from the Thermometer.
1665. Hooke, Microgr., vii. 38. Scaled Thermometers, which I have, by several tryals, at last brought to a great certainty and tenderness:… for graduating the stem, I fix that for the beginning of my division where the surface of the liquor in the stem remains when the ball is placed in … water, that is so cold that it just begins to freeze … (which I mark with an [0] or nought).
1687. A. Lovell, trans. Thevenot’s Trav., II. 30. lt is very hot in Aleppo,… the first day of June at Noon I found by my Thermometre, that the heat was at the thirtieth Degree.
1734. Berkeley, Analyst, § 50. Whether we can form an Idea or Notion of Velocity distinct from and exclusive of its Measures, as we can of Heat distinct from and exclusive of the Degrees on the Thermometer, by which it is measured?
1744. Phil. Trans., XLIII. 32. Fahrenheit,… so well known by his Mercurial Thermometers.
1782. Phil. Trans., LXXII. I. 72. Account of an improved Thermometer. By Mr. James Six.
1799. Monthly Rev., XXX. 9. In Pennsylvania, on the 14th of March,… Fahrenheit’s thermometer stood at 65° at noonday, though it had been at 14° but a week before.
1820. Register thermometer [see REGISTER sb.1 12].
1878. Huxley, Physiogr., 71. Dry-and-wet bulb Thermometers…. One of the instruments has its bulb free, whilst the other is covered with muslin. Ibid., 199. If a thermometer be buried in the ground…, it is found to be affected by all superficial changes of temperature.
1898. P. Manson, Trop. Diseases, viii. 158. The tongue now begins to moisten, the pulse-rate and the thermometer to fall.
b. fig.
1801. A. Hamilton, Wks. (1886), VII. 224. No bad thermometer of the capacity of our Chief Magistrate for government is furnished by the rule which he offers for judging of the utility of the Federal Courts.
1824. Byron, Juan, XVI. xlviii. Taste … now-a-days is the thermometer By whose degrees all characters are class’d.
1864. Lady Eastlake & Mrs. Jameson, Hist. Lord in Art, II. 265. Such forms of Art are, in this instance, the thermometer by which the temperature of the faith of the time may be ascertained.
1883. H. Smith, in J. G. Butler, Bible Work, II. 825/1. The true missionary spirit in the Church is … the test and thermometer of her piety.
c. attrib. and Comb., as thermometer bulb, piece, reading, scale, tube; thermometer-gauge, a steam-gauge that indicates the pressure in a boiler by the expansion of a fluid at the temperature due to the pressure; thermometer-stove, a stove automatically regulated by means of a thermometer.
1784. Wedgwood, in Phil. Trans., LXXIV. 367. Some of the clay thermometer pieces were set on end upon the silver piece.
1834. Mrs. Somerville, Connex. Phys. Sci., xv. 125. A glass tube of extremely fine bore, such as a small thermometer-tube.
1838. Civil Eng. & Arch. Jrnl., I. 129/2. The self-regulating fire, or thermometer-stove. Ibid. (1841), IV. 13/1. The four instruments employed … to determine the pressure of steam,… the barometer-gauge, the air-gauge, the thermometer-gauge, and the spring-gauge or indicator.
1901. Daily Chron., 26 Nov., 5/1. The downward tendency in yesterday’s thermometer readings.
