thermometer (thermometer)

[= F. ther momètre = Sp. termómetre, termómetro = Pg. thermometro = It. termometro = D. G. Dan. ther mometer = Sw. termometer, trum. structed, temperature is measured by the change in form of composite metal bars, due to their differential expansion (hence more properly called bimetallic thermometer ). One of the early forms was that of Bréguet, which consists of a fine spiral bar made of platinum, gold, and silver. One end of the spiral is fixed, the other end being connected with a simple mechanical device to convert the curving or torsion of the bar under changes of temperature into the movement of an index over a dial having a scale marked in a circle upon it. The same principle, with variations in the mechanical application, is now much used in the construction of thermographs. For indicating very slight variations of temperature a thermo-electric junction or the bolometer is employed. The thermometer discovers all the small unperceivable variations in the coldne of the air. Glanville, E ays, iii. (an. 1676). ( Richardson .) 2. Hence, figuratively, anything which (roughly) indicates temperature. These fixed animals [corals], and the reefs which they elaborate, are among the best of living thermometers . Gill , Proc. Biol. Soc. of Washington, 1885, II. 35. Aspiration thermometer, one in which the temperature of the air is obtained by drawing air in with a ventilating-fan through a tube, and causing it to flow rapidly over a thermometer, or over wet and dry-bulb thermom eters, placed therein. This method, first described by Belli in 1837, has been followed and developed in the instrument of A mann. - Attached thermometer, one fastened to the tube of a barometer for indicating the temperature of its mercury. Axilla thermometer. See axilla.- Bi-metal thermometer, a thermometer composed of a bar of two metals or alloys, having different rates of expansion, brazed together and sometimes bent into the form of a spiral. The compound bar is fastened rigidly at one end, the other end being connected with a simple mechanical device to convert the curving or torsion of the bar under changes of temperature into the thermometer movement of an index over a dial having a scale marked upon it. - Celsius thermometer, a thermometer introduced by Celsius in 1736 (and used to a limited extent), in which the zero of the scale was placed at the temperature of boiling water and 100° at the temperature of melting ice, plus (+) and minus (-) degrees in atmospheric temperatures being thus avoided. This was a centigrade scale, but not that of the modern centigrade thermometer, which was introduced by Linnæus. Centigrade thermometer. See def. 1.- Chromatic thermometer, an arrangement of gla plates, devised by Sir David Brewster, exhibiting the difference between their temperature and that of an object with which they are brought in contact by the different hues of the polarized light produced in the plates. - Chromo thermometer, an instrument used to raise the temperature of petroleum at the rate of 20° in fifteen minutes: used for purposes of testing. - Clinical thermometer, a small maximum self-registering mercurial thermometer used in obtaining the temperature of the body. In its usual form the range of scale is 25° F., or le , and graduation is carried to one fifth of a degree. A very sensitive clinical instrument, called the half - minute thermometer, has a bulb of small diameter and an extremely fine bore, in which the mercury is rendered visible by a lens-fronted stem. - Conjugate thermometer. Same as differential thermometer. Deep-sea thermometer, a registering thermometer used to ascertain the temperature of the sea at any depth. The instrument consists of the thermometer proper set in a metallic frame. The form of thermometer now used is that of Negretti and Zambra. It consists of a mercury thermometer whose stem, of wide bore, terminates in a small pyriform sac. The stem is contracted and contorted just above the bulb, and when the instrument is in verted, the mercury-column breaks at this point, and flows down into the tube, which is graduated in the inverted po metallic conductor. The difference in the resistance be tween a current pa ing through a conductor of known and one of unknown temperature gives the difference of temperature between the two. Also called differen tial -resistance thermometer. The most delicate form in which the principle is applied is the bolometer.-Fahrenheit thermometer. See def. 1.- Kinnersley's thermometer, an apparatus sometimes used to illustrate the sudden expansion of air through which a discharge of high-potential electricity has taken place. It consists of two connected tubes partially filled with water; the larger one contains above the water-surface two knobs, and when the spark is formed between them the water is forced up to a higher level in the smaller tube.Maximum thermometer, one that registers the maximum temperature to which it is exposed. Three types have come into use in connection with the mercurial thermometer. (a) The Rutherford maximum has a light movable steel index at the top of the mercurial column. The tube is placed horizontal, and as the temperature rises the mercury pushes the index before it. When the temperature falls, the index is left in situ to mark the position of the maximum. (b) In Phillips's maximum, a small bubble of air makes a break in the upper part of the mercurial column. When the temperature begins to fall, the detached portion of the column is left behind to register the highest temperature. (c) The Negretti maximum has the bore of the tube partly closed by a constriction just above the bulb. In rising temperatures mercury is forced from the bulb past the constriction, but when the temperature falls the mercury cannot readily return to the bulb, and the top of the mercurial column indicates the maximum temperature. In order to reset the thermometer to the current air-temperature, the mercury is forced back into the bulb by whirling the instrument on a swing-pin. This form of maximum is used at the stations of the United States Weather Bureau. - Mercury thermometer. See def. 1.- Metallic thermometer. See def. 1. Metastatic thermometer, a very sensitive mercurial thermometer, having an apical cavity thermometer into which any desired part of the mercury can be drawn off. This device enables the thermometer to be used over a wide range of temperature, and the scale to be graduated to small fractions of a degree, without increasing the length of the stem. For each different state of the instrument, the temperature corresponding to some part of the scale must be determined by comparison with a standard thermometer. Methyl-butyrate thermometer, one in which the thermometric substance is methyl butyrate. Sir William Thomson, Encyc. Brit., XI. 569.- Minimum thermometer, a thermometer that registers the minimum temperature to which it is exposed. The alcohol minimum, devised by Rutherford in 1794, is now universally used. The registration is effected by a light steel or gla index enlarged and rounded at the end, and wholly immersed in the column of alcohol. When the temperature falls, the index is carried toward the bulb by the surface-tension at the end of the contracting liquid column, and when the temperature rises the alcohol flows around and past the index, leaving it to mark the lowest temperature. - Optical thermometer, a thermometer proposed by Cornu for the study of high temperatures, based on the principle that in certain crystals the amount of the rotation of the plane of polarization depends on the temperature. As quartz can be submitted to a wide range of temperature, it is considered to be specially adapted for the application of this method in determining high temperatures.-Overflowing or mercurial-weight thermometer, a mercury-thermometer consisting of a bulb with a short piece of fine stem perfectly filled with mercury at 0° C. Any higher temperature is determined by weighing the quantity of mercury expelled, instead of by measuring it volumetrically, as in the ordinary mercurial stem thermometer. - Radiation thermometer. See terrestrial-radiation thermometer and solar - radiation thermom eter. - Réaumur thermometer. See def. 1.- Registering thermometer, a self-registering thermometer; a maximum or minimum thermometer. - Six's thermometer, a self-registering thermometer, invented by J. Six in 1781, combining in one instrument the registration of maximum and minimum temperatures: for many years very widely used, but now generally superseded by separate maximum and minimum instruments. - Sling thermometer, thermometer with which the tempera the free air. The resulting rapid convection brings the temperature of the thermometer into close accordance with the temperature of the air. - Solar-radiation thermometer, a thermometer for measuring the intensity of solar radiation. A form frequently adopted for this purpose is the black - bulb thermometer in vacuo, first suggested by Sir John Herschel. It consists of a sensitive mercurial thermometer having the bulb and about an inch of the stem obtained by whirling the covered with lampblack. The whole is inclosed in a gla tube, of which one end is blown into a large bulb in the center of which is fixed the bulb of the thermometer, and the tube is then exhausted of air. The thermometer-bulb thus prepared absorbs all the solar heat that falls upon it, and loses none by convection. With the black-bulb thermometer there is frequently used a bright-bulb ther mometer similarly incased. This has its bulb covered with polished silver, or some equivalent coating, which reflects most of the radiation that falls upon it. The difference between the readings of these two instruments is a umed to measure the intensity of solar radiation. - Sub marine thermometer. Same as deep -sea thermometer.Terrestrial-radiation thermometer, a minimum thermometer used to register the cooling of the earth's surface below the temperature of the air by nocturnal radiation. The bulb of the thermometer is generally shaped with special regard to obtaining a high degree of sensitivene . Also called nocturnal - radiation thermometer. - Upsetting thermometer, a form of mercurial thermometer devised by Negretti and Zambra for registering the temperature at any desired time. The registration is effected by inverting the instrument, after which it remains unaltered until it is reset. By means of clockwork, the upset may be made to occur automatically at any desired time, and a series of such thermometers constitutes a method for obtaining hourly temperatures. The instrument finds its principal use as a deep-sea thermometer. See above. Water-steam thermometer, a proposed form of ther mometer in which the thermometric substance is saturated water-vapor, and in which the temperature is given from the pre ure of the vapor as measured by the height of the water-column it can support. - Wet-bulb thermometer. See psychrometer.