THE 
The conjlruolion of the Mercurial Thermometer. 
In the manner, and with the fame caution as before, 
put a little quantity of mercury, not exceeding the 
bignefs of a Pea, into a tube B C, thus bent with 
wreaths y 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 
ferve 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 defe&ive in this, that 
they are liable to be adted 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 y and on the 
contrary, either an increafe of heat, or decreafe of 
weight of the atmofphere, will make it defcend. 
There being fome inconveniencies 
attending the Thermometers juft 
defcribed, another has been at- 
tempted, that fhould meafure heat 
and cold by the rarefa&ionandcon- 
denfation of fpirits of wine ; tho’ 
that be vaftly lefs than that of air, 
and confequently the alterations in 
the air likely to be much lefs fen- 
fible. 
The ftrudture 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 tindlure ; 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 the 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 how 
far it will retire in the extremeft 
cold. 
If it be (till at too great a diftance 
from the ball, part of it is to be taken 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 fldes is to be added 
a fcale, 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 confequently will afcend in 
the tube j and as the heat decreafes, the fpirit will 
defcend, and the degree or quantity of afcent and 
defcent will be feen in the fcale. 
THE 
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 refills 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 elafticity, will tend downward, and of confe- 
quence will refift the rife of the liquor, and be corn- 
prefled by it as it does rife j its elafticity therefore is 
thus increafed. 
3. Since it is found by experience, that a lefs degree 
of heat is communicated more eaflly to the fpirit of 
wine in the ball than a greater, the rarefadtions 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 eaflly 
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- 
fure of heat, &c. To which may be added, what 
Dr. Halley obferves in the Philofophical Tranladions, 
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, in different places, may be compared 
together. 
Some note the place the liquor is at in winter, when 
water begins 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 ; the middle point whereof anfwers in 
their graduation to temperate heat ; and each moiety 
they lubdivide 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 
the melting of all butter, as alio that all Thermome- 
ters receive the fame imprefiions 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 adtion of the temperate heat, may fhew 
the degree of temperate heat •, and laftly, they divide 
the intermediate fpace into fifteen or more equal parts 
which they continue beyond each extreme j but this 
method is liable to the like inconvenience with the 
former. 
Dr. Halley affumes, that for a fixed degree of heat, 
where fpirits of wine begin to boil ; but there is rea- 
fon to fufpedt this too of being precarious ; though, 
after him, Mr. Amontons retains the degree of heat, 
anfwering to boiling water, for the graduating his 
mercurial Thermometer : but as the different Speci- 
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. 
THERMOSCOPE, [of S^s, heat, and <rt£07T£W, 
I view.] An inftrument defigned to fhew the changes 
happening in the air, with refpedt 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- 
nifying an inftrument that ftiews or exhibits the 
changes 
