THE 



to exprefs any thing that warms the body, and by others 

 particularly for a warm fomentation, prcfcribed by Hippo- 

 crates for removing pains in the fide, and giving eafe in 

 pleiirifics. 



THERMES, in ytndent Geegraf/jy, a town of Hifpania 

 Citerior, S. of Numantia. 



THERMI, in Gtogr/iphy, a town of Afiatic Turkey, in 

 the province of Natolia ; 24 miles N. of Burfa. 



THERMIA, an illand in the Grecian Archipelago, fo 

 called from its abounding with hot fprings. It is not fo 

 mountainous as fome of the other iflands, and the foil, when 

 well cultivated, produces very large quantities of barley, 

 wine, and figs. The ifiand alfo affords plenty of honey, 

 wax, partridges, a great quantity of fine filk, and as much 

 cotton as the inhabitants require for their own ufe. The 

 Greek Chrillians in this ifiand are computed at 16,000. 

 Thermia is the fee of a bifhop, and contains fifteen or Cxteen 

 churches, .nnd feveral convents. On the ifiand areftiU vifible 

 the ruins of two cities ; one of which, on the fouth coaft, 

 mull have been of extraordinary fplendour. N. lat. 37° 20'. 

 E. long. 24^32'. 



Thermia, a town and capital of the ifland of Thermia. 

 N. lat. 37^ 24'. E. long. 24° 26'. 



THERMOMETER, Thermometrum, derived from 

 fltffjo,-, hiat, and ns^i', to mtafure, an inftrument (hewing, or 

 rather meafuring, the increafe and decreafe of the heat and 

 cold of the air. 



The degree of heat, as afcertained by a thermometer, is 

 only to be confidered in relation to the furrounding bodies, 

 by \-irtue of which a body fupports the equilibrium of tem- 

 perature, when it is in the neighbourhood of bodies equally 

 heated : thus, if a thermometer (lands at 60°, both in a veflTel 

 of water and in another of mercury, we may infer that the 

 water and the mercury may be mixed without any change 

 of their temperature ; but the abfolute quantity of heat con- 

 tained in equal weights, or in equal bulks, of any two bodies 

 at the fame temperature, is by no means the fame. See 

 Heat. 



The general principles upon which the conftruftion and 

 ufe of thermometers, or meafurers of heat depend, are ftated 

 and explained under the articles Calokic, Cold, Conge- 



LATIO.V, FilEEZlNG, HeAT, &C. 



It will be fufficient to obferve in this place, that the well- 

 known and moft general efFeft of heat, whether it be ob- 

 tained by comprefling a certain fubftance into a nan-ower 

 fpace, fo that a quantity of heat may come out of it and 

 be communicated to certain bodies, or by expanding a cer- 

 tain fubdance into a larger fpace, fo that it may abforb a 

 quantity of heat from furrounding bodies, and thus cool 

 thefe bodies, or in whatever other way it be procured, is 

 a dilatation of bodies, or an augmentation of their bulks. 

 The contrary effeft is produced by cold, «. e. by a diminu- 

 tion of the free caloric. Ilr muft, however, be obferved, 

 that bodies of equal bulks, but of different kinds, are not 

 expanded alike by being heated to the fame degree ; nor 

 are the increments of bulk in the fame body always pro- 

 portional to the quantities of heat which are communicated 

 to It. E. gr. if a given quantity of water, by being heated to 

 a certain degree, be increafed in bulk one cubic inch, the 

 addition of double or treble that quantity of heat will not 

 increafe its bulk two or three cubic inches refpeaively ; 

 therefore the expanfions of water are not proportional to the 

 increments of heat. 



The only prafticable method of meafuring the expanfions 

 of fluids, IS by inclofing them in certain velTels, and by mea- 

 i unng that part of the cavity of each xeM which is occupied 

 by the particular fluid which fillsit in different temperatures. 



3 



T H E 



It is evident, that the fubftance of the vefTel is alfo expanded 

 by the heat, and of courfe its cavity is enlarged. Therefore, 

 when we find that the bulk of the fluid is increafed, that 

 app;irent increment is only the difference between the en- 

 larged capacity of the velTel and the increafed bulk of the 

 fluid. For this reafon thofe velTels muft be made of fuch 

 fubftances as are leaft expanfible by heat. Indeed glafs 

 is the fubftance which is univerfally ufed for fuch pur- 

 pofes, both on account of its httle expanfibility, and of its 

 tranfparency, bcfides its having other remarkably ufeful 

 properties. 



A glafs velTel filled to a certain degree with a liquid, for 

 the purpofe of (liewing theexpanfion of that liquid in differ- 

 ent temperatures, or for the purpofe of (hewing the temper- 

 ature by the correfponding expanfion of that liquid, is called 

 a thermomeier. 



The thermometer and thermofcope are ordinarily ac- 

 counted the fame thing : Wolfius, however, makes a differ- 

 ence ; but fliews, at the fame time, that what we call ther- 

 mometers are, in reality, no more than thermofcopes. 



The invention of the thermometer is attributed to feveral 

 perfons by different authors, •viz. to Sandlorio, Galileo, 

 Father Paul, and Drebbel. The invention is afcribed to 

 Cornelius Drebbelius of Alcmaer, about the beginning of 

 the feventeenth century, by his countrymen Boerhaave 

 (Ghem. i. p. 152. 156.) and Mufchenbroeck, Introd. ad 

 Phil. Nat. vol. ii. p. 625. 



Fulgenzio, in his life of Father Paul, gives him the ho- 

 nour of the firft difcovery. Vincenzio V'iviani (V'it. de 

 I'Galil. p. 67. See too Oper. di Galil. pref. p. 47.) fpeaks 

 of Galileo as the inventor of thermometers. But Sanc- 

 torio himfelf (Com. in Galen. Art. Med. p. 736 — 842. 

 Com. in Avicen. Can. Fen. i. p. 22. 78. 219.) exprefsly 

 alTumes this invention ; and Borelli (De Mot. Animal, ii. 

 prop. 175.) and Malpighi (Oper. Pofth. p. 30.) afcribe it 

 to him without referve. Upon which Dr. Martine remarks, 

 that thefe Florentine academicians are not to be fufpefted 

 of partiality in favour of one of the Patavinian fchool. But 

 whoever was the firft inventor of this inftrument, it was very 

 rude and imperfeft ; and as the various degrees of heat were 

 indicated by the different contraAion or expanfion of air, it 

 was afterwards found to be an uncertain and fometimes a 

 deceiving meafure of heat, becaufe the bulk of air was af- 

 fected, not only by the difference of heat, but likewife by 

 the vai-iable weight of the atmofphere. 



There are various kinds of thermometers ; the conftruftion, 

 defefts, theory, &c. of which, are as follow : 



Conjlruciion of the Thermometer., depending on the RarefaHion 

 of the Air. — This aerial thermometer, which was that firft 

 invented by Drebbel, confifts of aglafstube B E (P/a/fXVI. 

 Pneumatics, Jig. i.), connefted at one end with a large glafs 

 ball A, and at the other end immerfed in an open v€(rei, or 

 terminating in a ball D E, with a narrow orifice at D ; 

 which veflTel, or ball, contains any coloured liquor that will 

 not eafily freeze. Aqua fortis tinged of a fine blue colour 

 with folution of vitriol or copper, or fpirit of wine tinged 

 with cochineal, or Brafil wood, will anfwer this purpofe. 

 But the ball, A, muft be firft moderately warmed, (b that a 

 part of the air contained in it may be expelled through the 

 orifice D ; and then the liquor prefTed by the weight of the 

 atmofphere will enter the ball D E, and rife, e. g. to the 

 middle of the tube at C, at a mean temperature of the wea- 

 ther ; and in this ftate the liquor by its weight, and the air 

 included in the ball A, &c. by its elafticity, will counter- 

 balance the weight of the atmofphere. As the furrounding 

 air becomes VTarmer, the air in the ball and upper part of 

 the tube, expanding by heat, will drive the liquor into the 



lower 



