i 



\ 



H 



ijiru^ion of 



In the manner, and with the fame caution as before, 

 put a little quantity of mercury, not exceeding the 

 blgnefs of a Pea, into a tube B C, thus bent with 

 wreaths ; that taking up the lefs height, it may be 

 the more manageable, and lefs liable to harm : di- 

 vide this tube into any number of equal parts, to 

 fervc for a fcale. 





' ; „' 



» , • 



Here the approaches of the mercury towards the ball 

 A, will fhew the increafes of the degree of heat. The 



reafon is the fame as in the former. 

 But both thefe inftruments are defeftive in this, that 

 they are liable to be afted on by a double caufe ; for 

 not only a decreafe of heat, but alfo an increafe of 

 weight of the atmofphere, will make the liquor rife 

 in the one, and the mercury in the other ; and on the 

 contrary, either an increaie of heat, or decreafe of 

 weight of the atmofphere, will make it defcend. ' 



There beino; fome inconveniencies 

 attending the Thermometers juft 

 defcribed, another has been at- 

 tempted, that Ihould meafure heat 

 and cold by the rarefa6bionandcon- 

 denfation of fpirits of wihe';.''tIio' 

 that be vaftly lefs thari that of air, 

 and confe'quently the alterations in 

 ' : the air likely to be much lefs fen- 



^ fible. 



The ftrudure of this Thermometer 

 is this : on fome little pieces of 

 Turmerick is poured a quantity of 

 fpirit of wine, which hereby re- 

 ceives a red tin£ture -, this being 

 done, the fpirit of wine is filtrated 

 through a brown paper, that the 

 coarfer particles of the root may 

 be feparated therefrom : with the 

 fpirit thus tinged and prepared, 

 they fill a glafs ball with a tube, 

 and that all the fpirit may not de- 

 fcend in winter into the ball, it is 

 convenient to ^ put tlie ball into a 

 lump of fnow mixed with fait ; or, 

 if the inftrument be to be made 

 in fummer, into fpring water, 

 impregnated with faltpetre, that 

 the condenfed fpirit may fhew |iow 

 far it will retire in the extrerpeft 

 cold. i 



-I 



If it be ftill at too great a diflance 



T H 



Yet, as the ratio of yefterday's heat to to-day's, is not 

 hereby difcovered, this inftrument is not ftridly a 

 Thermometer, any more than the former. 

 Here it is to be obferved •, 



1. That as the natural gravity of the liquor makes 

 it tend downward, fo it refifts its afcent out of the 

 ball into the tube, and that the more as it rifes high- 

 er, for which reafon it were beft to have the tube ho- 

 rizontal. 



2. Since there muft of neceffity be fome air left in 

 the void part of the tube over the liquor, that air, 

 by its elallicity, will tend downward, and of confe- 

 quence will refift the rife of the liquor, and be com- 

 prefled by it as it does rife ^ its elafticity therefore is 

 thus increafed. 



3. Since ic is found by experience, that a lefs degree 

 of heat is communicated more eafily to the fpirit of 

 wine in the ball than a greater, the rarefaftions of 

 the fpirit of wine are not proportionable to their pro- 

 ducing caufes ; efpecially a greater degree of heat 

 finds more liquor in the tube than a lefs does •, to 

 which, notwithftanding, the heat may be more eafily 

 communicated than to that ftagnating in the ball. 

 On thefe accounts, this laft Thermometer, called the 

 Florentine Thermometer, becaufe contrived by the 

 Academifts del Cimento, though it is that which is 

 in common ufe, is far from being an accurate mea- 





4'. 

 V 



r 



r « 



-.i. 



\~- 



fure of heat, &c. To v/hich may be added, what 

 Dr. Halley obferves in the Philofophical Tranfadlions, 

 that he has learned from thofe that have kept fpirit of 

 wine long, that it lofes part of its expanfive force in 

 courfe of time. 



Various authors have propofed various methods for 

 finding a fixed point or degree of heat and cold, from 

 which to account for the other degrees, and adjuft 

 the fcale -, fo that obfervations made at the fame or 

 different times, indifferent places, may be compared 

 together. ." 



; Some note the place the liquor is at in winter, when 



'■water begms to freeze; and again that in fummer, 



when butter placed near the ball of the Thermometers, 



melts. The intermediate fpace they divide into two 



equal parts; themiddle point whereof anfwers in 

 their graduation tptebiperate heat ; and each moiety 



^-''they fubdivide into ten degrees, adding four other 



^; equal degrees on each of the two extremes. 



"^ But this method fuppofes the fame degree of heat 



and cold to anfwer to the freezing of all water, and 



■ ■ 





' - < * 

 » (, ^ — " 





from the ball, part of it is to betaken out ; and that 



.. the tube may not be much longer than needs, it is 



' convenient to immerge the ball, filled with its fpirit, 



in boiling water, and to mark the fartheft point to 



which the fpirit then rifes. 



At this point the tube is to be hermetically fealed by 



the flame of a lamp ; and at the fides is to be added 



a 



re 



as in the former Thermometers. 



Now the fpirit of wine rarefying and condenfing very 

 confiderably, as the heat of the ambient air increafes, 

 the fpirit will dilate, and corifequently will afcend in 

 the twbef ; and as the heat decreafes, the fpirit will 

 defcend, and the degree or quantity of afcent and 

 defcent will be feen in the fcale. ' . 



1 - 



-* > / 



the melting of all butter, as alfo that all Thermome- 

 ters receive the fame impreffions from the fame degree, 

 of heat ; all which are contrary to experience. 

 Others advife, that the ball of the Thermometer be 

 put into any quantity of fnow and fait, and the point 

 the liquor'is at to be noted; and that thence the 

 Thermometer be removed into a deep cave or cellar, 

 whither no external air reaches; fo that the liquor 

 receiving the aflion of the temperate heat, may (hew 

 the degree of temperate heat ; and laftly, they divide 

 the intermediate fpace into fifteen or more equal parts 

 which .they continue beyond each extreme ; but this 

 method is liable to ' the like inconvenience with the 



former. 



Dr. Halley afTumes, that for a fixed degree of hear> 



where fpirits of wine begin to boil ; but there is rea- 

 fon to iufpeft this too of being precarious; though, 

 after him, Mr. Amontons retains the degree of heat, 

 ahfwering to boiling water, for the graduating his 

 mercurial Thermometer : but as the different fpeci- 

 fic gravities of water argue a different mafs or tex- 

 ture, it is highly probable, that the heat of all boil- 

 ing waters is not the fame, fo that the point is yet 



undetermined. 



HER MO SCOPE, [of ^sp^^sy heat, and (ry.oTn^y 



I view.] An inftrument defigned to ftiew the changes 

 happening in the air, with refpeft to heat and cold. 

 The name of Thermofcope is indifferently ufed with 

 that of thermometer ; however, there is fome diffe- 

 rence in the literal import of the words ; the firll fig- 



nifyine; an inftrument that ftiews or exhibits the 

 . '' - - ... - changes 



