THERMOMETER. 



thermometers made with oil, or any other vifcid hqiior, viz. 

 that fuch a liquor adheres too mucli to the hdcs ot the tube. 

 In a fudden cold or fall of the oil, much of it ilicks by the 

 \yay, and only links ^aduallv afterwards, fo that at hrll tlic 

 furface appears reallr lower than the prcfeiit tempcrature 

 requir.'S. And brlides, as at all times lome of the oil mull 

 continue to (lick and moillen the iniide of the tnbe, in dif- 

 ferent degrees of heat and cold, the oil, becoming alternately 

 more or lefs vifcid, will adhere fometimes more and fomotinies 

 K-fs J and will, therefore, inevitably difturb the regularity 

 and uniformity of the thermometer. Marline's Effays, 



Eff. iii. ^ , , 



ThkRMOMKTe li>;, Fixtii Points of. \ arious methods have 

 been propofed by various authors,' for finding a fixed point, 

 or degree, of heat and cold, from which to reckon tlie other 

 degrees, and adjuft the fcale ; fo that obfcrvations made at 

 the fame or different times, in different places, might be com- 

 pared together. For want of this, notwithftanding all the 

 numerous regiflers of the weather, &c. that have been kept 

 and publilhed by different authors, we are much at a lofs to 

 determine the comparative differences of heat and cold in 

 different countries and cHmates, and the refultof many other 

 obfervations. If all the weathcr-glaffes in the world had 

 been made according to one determined fcale, thefe incon- 

 veniences and uncertainties would have been prevented ; 

 which, indeed, are now unavoidable, and mufl ftill continue 

 fo, till all agree to graduate their thermometers in the fame 

 manner, or at lead deteiTnine fome fixed or unalterable points 

 of heat, to which all the different fcalcs of thofe inftruments 

 may be reduced. The honourable Mr. Boyle was very 

 feniible of this inconvenience, and much laments it ; and he 

 propofed the freezing of tiie effcntial oil of anifeeds, as a 

 term of heat and cold that might be of ufe in making and 

 judging of thermometers, and fo to graduate them from this 

 point according to the proportional dilatations or contrac- 

 tions of the included fpirits. He mentioned alfo the cold- 

 nefs requifitc to begin the congelation of diftilled water as 

 another fixed term that might be adopted ; for he was per- 

 fuadcd, that among the ordinary waters, fome were apt to 

 freeze more cafily than others. But he was deterred from 

 profecuting this fcheme of fixing a ftandard for m>aking and 

 graduating all thermometers in the fame way. Experi- 

 ments, &c. on cold, in his works abridged by Shaw, vol. i. 



P- 579- 



Dr. Hallcy (Phil. Tranf. Abr. vol.ii. p. 36.) feems to 

 have been fully apprized of the bad effefts of the indefinite 

 method of conftructing thermometers, and wlfhed to have 

 them adjufled to fome determined points. What he feems 

 to prefer for this purpofe is the degree of temperature 

 which is found in fubterranean places, where the heat in 

 fummer and cold in winter appears to have no influence. 

 But this degree of temperature is fhewn by Dr. Marline to 

 be a term for the univerfal conftruCtion of thermometers, 

 both inconvenient, as it cannot be eafily afcertained ; and a 

 precarious one, as the difference of foils and depths may 

 occafion a confiderable variation. Another term of heat 

 which he thought might be of ufe in a general graduation of 

 Ihermometers, is that of boiling fpirit of wine that has 

 been highly reftified : but a much more convenient term 

 of heat, though lefs infifted on by Dr. Halley, is that 

 of boiling water. The firfl trace that occurs of the me- 

 thod of aftually applying fixed points or terms to the ther- 

 mometer, and of graduating it, fo that the unequal divi- 

 fions of it might corrcfpond to equal degrees of heat, is the 

 projca of Renaldiuus, profcfTor, of Padua, in 1694: it is 

 thus defcribed in the Afta Erud. Lipf. " Take a flender 

 tube, about four pabns long, with a ball faflcncd to the 



fame ; pour into it fpirit of wine, enough jufl to fill the" 

 ball, when furrounded with ice, and not a drop over : in 

 this ilate, feal the orifice of the tube hermetically, and pro- 

 vide twelve vefTels, each capable of containing a pound of 

 water, and fomewhat more ; and into the firfl pour eleven 

 ounces of cold water, into the fecond ten ounces, into the 

 third nine, &c. : this done, immerge the thermometer in the 

 fird veffel, and pour into it one ounce of hot water, ob- 

 ferving how high the fpirit rifes in the tube, and noting the 

 point with unity : then remove the thermometer into the 

 fecond velTel, into which are to be poured two ounces of 

 hot water, and note the place the fpirit rifes to with 2. By 

 thus proceeding till the whole pound of water is fpenl, the 

 inflrument will be found divided into twelve parts denoting 

 fo many terms or degrees of heat ; fo that at 2 the heat is 

 double to that at i, at 3, triple, &c." 



But this method, though plaufible, Wolfius fhews, is 

 deceitful, and is built on falfe fuppofitions ; for it takes for 

 granted, that we have one degree of heat, by adding one 

 ounce of hot to eleven of cold water ; two degrees, by 

 adding two ounces to ten, &c. : it fuppofes, alfo, that a 

 fingle degree of heat afts on the fpirit of wine in the ball 

 with a fingle force ; a double with a double force, &c. • 

 laftly, it fuppofes, that if the cffeft be produced in the 

 thermometer by the heat of the ambient air, which is here 

 produced by the hot water, the air has the fame degree of 

 heat with the water. 



Soon after this projeft of Renaldinus, viz. in 1701, fir 

 Ifaac Newton conftrufted his oil thermometer, and fixed 

 the bafe or lowefl fixed point of his fcale at the tempera- 

 ture of thawing fnow, and twelve at that of the human 

 body, &c. in the manner explained under the article Oil 

 Thermometer. 



M. de Luc obferves, that the fecond term of his fcale 

 fhould have been at a greater diftance from the firft, and 

 that the heat of boiling water would have anfwered this 

 purpofe better than that of the human body. 



In 1702, M. Amontons contrived his aniwr/a/ thermome- 

 ter, the fcale of which was graduated in the following man- 

 ner. He chofe for the firfl term the weight that counter- 

 balanced the air included in his thermometer, when it was 

 heated by boiling water : and in this ftate he fo adjufled 

 the quantity of mercury contained in it, till the fum of its 

 height in the tube, and of its height in the barometer at 

 the moment of obfervation, was equal to feventy-three 

 inches. Fixing this number at the point to which the 

 mercury in the tube rofe by plunging it into boiling water, 

 it is evident, that, if the barometer at this time was twenty- 

 eight inches, the height of the column of mercury in the 

 thermometer above the level of that in the ball was forty- 

 five inches ; but if the height of the barometer was lefs by 

 a certain quantity, the column of the thermometer ought to 

 be greater by the fame quantity, and reciprocally. He 

 formed his fcale on the fuppofition that the weight of 

 the atmofphere was always equal to that of a column 

 of mercury of twenty-eight inches, and divided it into 

 inches from the point 73 downwards, marking the divi- 

 lions with 72, 71, 70, &c. and he fubdivided the inches 

 into lines. 



But as the weight of the atmofphere is variable, the ba- 

 rometer mufl be obfervcd at the fame time with the thermo- 

 meter, that the number indicated by this lafl inflrument 

 may be properly corrected, by adding or fubtradling the 

 quantity of which the mercury is below or above twenty- 

 eight inches in the barometer. In this fcale, then, the 

 freezing point is at 51^ inches, correfponding to gr. 

 32 of Fahrenheit, and the heat of boiling water at 73 



inches. 



