THL 



the scale contains 80 between the freezing 

 and boiling points of water. The Centi- 

 grade thermometer is decidedly the most 

 convenient. 



THER'MOSCOPE, from Otfus/i, heat, and 

 ffxmca, to view. An instrument for ex- 

 hibiting the effects of heat. 



THERMO'STAT, from 6eiwj, heat, and 

 ff'raTos, standing. The name of an ap- 

 paratus for regulating temperature in dis- 

 tillation, hot baths, hothouses, &c., pa- 

 tented by Dr. Ure in 1831. It operates 

 on the well-known principle, that when 

 two metallic bars, differently expansive, 

 are ri vetted or soldered faceways together, 

 any change of temperature in them will 

 cause the compound bar to bend in one 

 direction or the other; and these move- 

 ments are made to operate in regulating 

 valves, stop-cocks, stove-registers, &c.,so 

 as to regulate the temperature of the 

 media In which the compound bars are 

 placed. 



THE'SIS, 0<r/. 1. A position or proposi- 

 tion, which a person advances and offers 



to maintain. 2. In logic, a subject is 



divided into thesis and hypothesis ; thesis 

 contains the thing affirmed, and hypothesis 

 the conditions of the affirmation or nega- 

 tion. 3. In music, the depression of the 



hand in beating of time 



THE'THYS. The name given by Linn, to 

 a genus of gasteropods, of the order Nudi- 

 branchiata, Cuv. The T.fimbria, Lin., a 

 beautiful species from the Mediterranean, 

 is well known. 



THE'URGY, &ss and egyov, work. The 

 working of miracles. 



THIM'BLE. In nautical language, an iron 

 ring, with a hollow or groove round its 

 circumference, to receive the rope which 

 is spliced round it. 



THIN-OUT. A term in geology for the 

 gradual thinning of a bed or stratum, till 

 it wholly disappears. 



THIRD. In music, an interval containing 

 three diatonic sounds; the major com- 

 posed of two tones, and the minor con- 

 sisting of a tone and a half. 



THIRL'AOE. In law, a contract or power 

 to prevent the tenants of certain di-tricts 

 Irom carrying their corn to be ground 

 any where else than at a particular 

 mill. 



THIS'TLE. 1. In botany, -^see C\RDUUS, 

 SEBBATCLA, CENTAUREA, and CARLISA). 

 2. A Scottish order of knighthood. 



THLAS'PI. The Bastard-cress: a genus 

 of herbaceous plants : TetradynamiaSili- 

 culosa. Name from 6>.acu, to break, be- 

 cause the seeds appear as if they were 

 bruised. There are four British species, 

 of which the penny-cress or treacle mus- 

 tard IT. arvense) is the best known. 



713 T H O 



THOLES, \ Sax. thai, a peg. 1. Tim 



THOWLZS, J pins inserted into the gun- 

 wale of a boat to keep the oars in the 



rowlocks when used in rowing. 2. The 



handles of a scythe. 



THO'MISTS. Followers of Thomas Aqui- 

 nas, in opposition to the Scotists. 



THOR. In mythology, the god of thun- 

 der; a deity worshipped by the northern 

 nations, and from which our Thursday 

 derives its name. By our Saxon ancestors 

 he was believed to have extensive do- 

 minion in heaven, and that all nations of 

 the earth owed him divine honour and 

 service ; that he governed the winds and 

 clouds, and showed his displeasure by 

 causing lightnings, thunders, and tem- 

 pests, with excessive rains, hail, and 

 stormy weather ; but being well pleased 

 by adoration and sacrifice, he bestowed 

 upon his supplicants fair and seasonable 

 weather, and caused plenty of corn and 

 fruits to grow 



THORA'CIC. 1. Appertaining to the 

 thorax or chest. Thus the trunk of the 

 absorbents is named the thoracic duct from 

 its position. 2. In ichthyology, belong- 

 ing to the order Thoraeici. 



THORA'CICI. The third order of bony 

 fishes in the system of Linne 1 , respiring 

 by means of gills only, and having the 

 ventral fins under the pectoral, . e. under 

 the thorax. 



THO'RAX. The chest, or that part of the 

 body between the neck and abdomen : 

 from foam, to leap, because in it the 

 heart leaps. The thorax is divided by 

 imaginary lines into certain regions. 

 These are the right and left humeral, a 

 right and left subclavian, a right and left 

 mammary, a right and left axillary, a 

 right and left subaxillary , a right and left 

 scapulary, a right and left intrascapulary , 

 and a right and left subscapulary . 



THOR'INA. A primitive earth discovered 

 in 182S by Berzelius, in the mineral tho- 

 rite, of which it constitutes 58 per cent. It 

 is a fine white powder, the basis of which 

 is thorinum. 



THOR'INUM. The metallic basis of 

 thorina. It is obtained in an iron-gray 

 powder, the particles of which have a 

 metallic lustre. Like aluminum it ap- 

 pears to be malleable, and is not oxidised 

 by water, even when heated ; but when 

 heated in the open air it takes fire, burns 

 with much splendour, and is converted 

 into thorina. The earth thus formed is 

 snow-white, and exhibits no traces of ,- 

 fusion. 



THO'RITE. A black mineral, like obsi- 

 dian, discovered by Esmark of Christiana, 

 in Norway, and thus named by Ber/elius, 

 who analysed it. It occurs in the syenite 

 of the isle of Lov on, near Brevig, in 

 Norway, and i* very scarce. 



