THERMOMETER. 



for the geneial rcfulls of wbich wc refer to the article 

 Heat ; and for a more minute detail to Leflie's " In- 

 quiry into the Nature of Heat ;" and for an extonfive 

 abftraft, to an elaborate article on Caloric in Aikin's Dic- 

 tionary. See alfo our articles Caloric, Radiant Rays, 

 &c. &c. 



Thermometer, Balance, an inftrument invented by Mr. 

 James Kewley, of the Ifle of Man, and for which he ob- 

 tained a patent for Scotland, daLed Nov. ^, 1816; for Eng- 

 land, dated Nov. 21, 1816 ; and for Ireland, dated Jan. 4, 

 1817. This inftrument (befides anfvvering the purpofe of 

 afcertaining the temperature) is ufed as a firft moving power 

 for putting machinery into motion, for the purpofe of regu- 

 lating the temperature, by opening or clofing the flues, 

 windows, or doors of the apartment in which it is placed. 

 This invention mull therefore be of great importance to the 

 horticulturift ; as by it the artificial climate of hot-houfes, 

 confervatories, hot-beds, &c. can be accurately regulated, 

 without the leaft attention from the gardener, farther 

 than occafionally to wind up the machine to which it is 

 attached. 



In Plate XVI. Pneumatics, jig. 1 8. is a perfpedlive reprefent- 

 ation of Kewley's balance tiermometer. A is a glafs tube, 

 with its bulbs c and d hermetically fealed at e, and having a 

 very fine aperture sxf, for the admiffion of the prelFure of 

 the atmofphere upon the furface of the quickfilver con- 

 tained in the bulb d: g \s ?i milled-headed nut, let into a 

 mortife in the frame h, having a female fcrew in its centre, 

 through which the fcrew ;' is made to pafs. This nut ferves to 



elevate or deprefs the tube with the two clamping-pieces 

 (between which it is fcrewed fall) in the frame h, for the 

 purpofe of adjufting the inftrument to its proper centre o£ 

 gravity : /■ is a milled nut, having a pinion on its arbor, and 

 ferves the j)urpofc of moving the fcale / to the right or left, 

 as may be required : m and n are the knife-edged centres, on 

 which the inltrument fwings in any ornamental frame that the 

 poircfTor may choofe. When the inftrument is at the mean 

 temperature of its range, the bulbs c and d ought to be 

 each about half full, and the fmall tube communicating 

 with the bulbs quite full of quickfilver ; and the large tube, 

 and lialf of the bulb c, full of alcohol. Now it is evident, 

 that when the alcohol in the large tube expands by an in- 

 creafe of temperature, it muft prefs upon the furface of the 

 quickfilver in the bulb c, and force a quantity of quick- 

 filver, equal to its expanfion, into the bulb d : the centre of 

 gravity of the inftrument will thereby be altered, and it will 

 turn upon its centres, like the beam of a pair of fcales ; 

 therefore, when the temperature is defircd to be known, the 

 fcale is to be moved by turning the nut k, in order to bring 

 the inftrument to a balance ; when that is done, the degree 

 is read off" at 0. When this inftrument is ufed as a firft 

 moving power, to regulate the temperature of hot-houfes, 

 &c. it has a lever or wheel attached to one of its centres,, 

 which communicating with machinery, puts it in motion 

 when the temperature is either higher or lower than the 

 degree defired, which motion opens or clofes the windows, 

 flues, &c. as may be necefiary, until the degree of tempe- 

 rature to which the inftrument is at be produced. 



