THERMOSTAT, or is an apparatus invented and patented in 1831 by Dr. Ure, for regulating temperature in the processes of vaporisation and distillation, in heating baths and hot houses, in adjusting the draught of stoves'and.furnaces, in ventilating apartments, &c. Recta upon the principle that when two thin metallic bars, of different degrees of expansibility, are riveted or soldered side by side, any change of temperature will cause a sensible flexure in the compound bar ; the side consisting of the least extensible metal be coming concave, and the other convex. By this flexure of the com pound bar, which takes place with considerable force, a movement is effected, which, by the intervention of levers, may be made to open or close stop-cocks, dampers, ventilators, or any description of valves, and thereby to regulate the flow of heated liquids or the admission and emission of air. The principle of the thermostat may be applied in many different ways, of which the following may serve as examples. In fly. 1, a is the compound bar, firmly fixed at b. To the other, or free end of the compound bar, is attached, by means of a connecting rod, the short end of a lever mounted upon the axis of a circular revolving valve, or ventilator, c; and from the longer cud of the lever is sus pended a sliding valve, or damper, d. By increasing the temperature of the chamber or vessel in which the thermostat is placed, the com pound bar will assume the curved form indicated by the dotted lines, by which means the position of the lever will be altered, the valve c will be turned on its axis, and the damper will be raised. Fig. 2 shows another arrangement, in which two compound bars, a, a, fixed at b, are made to open• and close a valve, c, in a pipe through which air, water, or any other fluid is passed. By increasing the temperature of the apparatus, the upper or moveable ends of the bars would recede from each other, and, consequently, alter the position of the valve. Fig. 3 shows the principal part of a thermostatic apparatus in which three pairs of compound bars, a, a, a, are used to give motion to a sliding-rod d, d, with which any kind of valve may be connected by a rack and pinion, a chain and pulley, or otherwise. b, b, in this figure, is a straight guide-rod, which is fixed at one end by a screw-nut c. The thermostatic bars are nearly or quite straight when cold, and become more or less curved by the action of heat ; but in some modifications of the apparatus the bars are always curved, and the action of the apparatus depends upon the increase or decrease of the ordinary flexure. Fig. 4, for example, represents a thermostatic hoop, a, a, which may be immersed horizontally beneath the surface of the water-bath of a still. The hoop is fixed at 1,, and to its free ends are attached short links c, c, which impart longitudinal motion to the rod d. e is a lever-handle moved by the sliding-rod, and turning a valve on its axis f. The outer end of this lever carries an index, which moves against a graduated scale. g is a screw-nut, moveable upon the sliding-rod to adjust the apparatus before graduating the scale or are traversed by the index. [PYROMETER.]
THES310P1fO'RIA (Oesrpoquipta), a festival with mysteries in honour of DEMETER, to whom all the institutions of civilised life, especially of civil and religious laws, were attributed. The festival of the Tbesmophoria especially referred to this part of the character of the goddess, as is clear from several of the ceremonies observed at its cele bration, and from the surname of the goddess, " Tbesmophoros," from which the festival derived its name. It was celebrated in various towns in Greece, and in the Greek colonies, as Sparta, Thebes, Eretria, Ephesus, Syracuse, Agrigentum, and others. But the place where it was held with the greatest solemnity, and where the particulars of its celebration are best known, was Athens. It was introduced at Athens, according to some writers, by Orpheus, and according to Herodotus (ii. 171) by the daughters of Daman), from Egypt. Its celebration was confined to women, especially married women. It commenced every year on the Ilth of Pyanepsion, and lasted three days, though some writers extend it to four or even five. The discrepancy in this case, as well as in that of other Greek and Roman festivals, seems to have arisen from the circumstance that the real festival was in many instances preceded by one or more days devoted to preparations and purifica tions, and that some writers reckoned these days as belonging to the festivaL Previous to its celebration, the women of each demos elected from among themselves two matrons to conduct the solemnities, whose husbands, provided they had received a dowry of not less than three talents, had to pay the expenses of the festival as a liturgy. (buena, ' De Cironis Ileredit.; p. 208). The first day of the festival was called grobos or safbaor, that is, the procession ; because the women went from Athens to Eleusia in a procession in which they carried on their heads certain laws (Ourpot) written either in books or upon tablets. During the night between the first and second day the women solem nised their mysteries at Eleusis. The second day, called vna-reia, or " The Fast," was a day of mourning, on which the women were not allowed b• take any other food than cakes of sesame and honey, and the greater part of it they spent sitting in mournful attitudes on the ground around the statue of the goddess. Meursius and others think that the procession to the Thesmophorion (the temple of Demeter Thesmophoros) at Athens, which is alluded lo by Aristophanes Thesmopbor.; 276, &c.), and in which the women walked behind a waggon laden with baskets containing mystic symbols, took place in the afternoon of this day, the whole of which was a sacred day at Athens, on which neither the senate nor the people were allowed to hold their usual meetings. The third day was called KaAXryiveta, a surname of Demeter, by which she was invoked on this occasion. (Aristoph., ' Thesmophor.; 296, with the Scholiast.) On this day the women made up for the (lay of mourning, and indulged in various kinds of merriment, in imitation of Lambe, who was believed to have created a smile on the face of the goddess during her grief.