THE
731
THE
Fahrenheit's, which is generally used inGreat Britain . It is also used throughoutthis work, iui'e-s some other is mentionedReaumur’s, which is generally used inFrance and other parts ot tile Continent ...
Celsius’s, which has keen used chiefly inSweden , hence it is aho called the Swedish thermometer. It inis been lately adopt-ed by the French chemists, under the name
of centigrade thermometer..
The Florentine thermometers, whichwere made and used by the members ofthe famous academy del’ Cimento, beingsome of the first instruments of the sort,
"ere vaguely gsaduated, some having agteat many more degrees than others, lluttwo of their most common graduations seem
to be...
The Parisian thermometer, viz. the an-oienne thermometre of the Academy ofSciences , seems to have been graduated
nearly thus.
De la Hire’s thermometer, which stoodhi the observatory at Paris above 60 years,
"’as graduated thus.
Amanton’s.
Poleni’s.
De L’ Isle’s thermometer is graduated in
an inverted order.
Hales’s.
The Edinburgh thermometer, formerlyUsed, seems to have been graduated thus
These are the chief thermometers that have been used in Eu-rope ; and the temperatures indicated by the principal of them'nay be reduced into the corresponding degrees on anv of theothers, by means of the following simple theorems; in which Ralgnifies the degrees on the scale of Reaumur, F those of Fahren-heit's, and S those of the Swedish thermometer.
1. To convert the degrees of Reaumur into those of Fahrenheit;R X 9
■~T-+32 = F.
2 - To convert the degrees of Fahrenheit into those of Reaumur;
^l r 32 ) X 4 _
9 “ *
3 - To convert the Swedish degrees into those of Fahrenheit;^5—+32 = F.
F reez-ing-point.
Boil-
ing
point.
Deg. betweenthe preceding
two points.
32
212
180
0
SO
80
0
100
100
( 20
174
154
(13*
Slf
68-|
25
239
214
28
1994
1714
51*
73
2lj
4? 8
62 ft
150
0
150
0
34
34
0
163
163
8}
47
38f
• ( F ~ 32) X9
= S.
- = R.
6 - To c,
convert Reaumur’s degrees into Swedisli;
R X
-=S.
T
readers as are unacquainted with the algebraic expres-F"o r “'‘^nnetical formulae, it will be sufficient to express one orgre e °r l J iese in words, to explain their use: 1. Multiply the <j e -tie„t°‘ Reaumur by 9, divide the product by 4, and to the quo-r «uh e q ' 32 ’ tlle 1,11111 L ' x P resse;i the degree on the scile of Kali-2, From the degree of Fahrenheit subtract 32, multiply
the remainder by 4, and divide the product by 9, the quotient isthe degree according to the scale of Reaumur, &c. In order moreclearly to exhibit a comparative view of the different thermometers,we have given them in Plate CLXXIV. in the same order asthey were arranged by Dr. Martine in his valuable Essay on theConstruction and Graduation of Thermometers, and at the sametime adding those of Celsius and De Luc. Thermometers havebeen made of a great variety of shapes and sizes, suitable to the-different purposes for which they were intended. Thermometersfor shewing the temperature of the atmosphere, need not havetheir scales much extended ; it is more than sufficient if they goas high as 120°. The lower degrees may be carried down as lowas may be necessary for the cold of any particular climate. Themercurial thermometer needs not to be graduated lower than 40°below p, because at about that degree mercury ceases to be a fluid.
I hermometers which are to be situated in the open air out of thehouse, must he at some distance (at least a foot) from the wall,,and where the light of the sun may not fall directly upon them,F'lg. 3, represents a thermometer of the most usual shape, inde-pendent of the case. F'or chemical purposes, the bulb, and partof the lube of the thermometer, must project some way below the-scales, in order that they' may be placed in liquids, mixtures, &c.For other purposes, as for botanical observations, hot-houses,brewing-manufactories, baths, &c. the thermometers must bemade longer, or shorter, or narrower, or particular directionsmust be added to the scales, &c. but we shall not take any farthernotice of those fluctuating varieties of shape only. It is necessary,however, to describe a sort of thermometers which have beenconstructed for a particular purpose; namely, for shewing thehighest degree «f heat or of cold which has taken place during theabsence of the observer; as for instance, in the course of thenight, or in the hottest part of the day, or even during a wholeseason. Thermometers for this purpose have been contrived dif-ferently by various ingenious persons, as by Bernoulli), Kroft,Lord Charles Cavendish , &c. but the best of them, which how-ever is not without faults, and of course is in need of improvements,was contrived by Mr. James Six , and is described in the 72ncVvol. of the Philosophical Transactions . Fig. 4, exhibits this in-strument, but divested of the scale and frame; ab is a tube otthin glass, about l6 inches long, and , 5 S of an inch in diameter;cdefgh, a smaller tube with the inner diameter, about -ft, joinedto the larger at the upper end b, and bent down, lirst on the leftside, and then, after descending two inches below ab, upwardsagain on the right, in the several directions ede, fgh, parallel to*and one inch distant from it. On the end of the same tube at h,the inner diameter is enlarged to half an inch from /) to i, whichis two inches in length. This glass is filled with highly rectifiedspirit of wine, to within half an inch of the end i, excepting thatpart of the small tube trorn d to g, which is filled with mercury.From a-view of the instrument in this state, it will readily b&conceived, that when the spirit in the large tube, which is the bulbof the thermometer, is expanded by heat, the mercury in thesmall tube on the leftside will be pressed down, and consequentlycause that on the right side to rise; on the contrary, when thespirit is condensed by cold, the reverse will happen, the mercuryon the left side will rise as that on the right side descends. Thescale, therefore, which is Fahrenheit’s, beginning with 0, at thetop of the left side, has the degrees numbered downwards, whilethat on the right side, beginning w ith 0 at the bottom, ascends.The divisions are ascertained by placing this thermometer with agood standard mercurial one in water, gradually heating or cool-ing, and marking the divisions of the new scale at every 3 . I hemethod of shewing bow high the mercury had risen in the obser-ver's absence, is effected in the following manner: within thesmall tube of the thermometer, above the surface of the mercuryon either side, immersed in the spirit of wine, is placed a small in-dex, so fitted as to pass up and down as occasion may require ;that surface of the mercury which rises carries up ths index withit, which index does not return with the mercury when it descends;but, by remaining fixed, shews distinctly, and very accurately,how high the mercury had risen, and consequently vvhat degree ofheat or cold had happened. Fig. 5, represents those indexesdrawn larger than the real ones, to render it more distinct; a is asmall glass-lube f of an inch long, hermttically sealed at each end,inclosing a piece of steel-wire, nearly of the same length ; at each
end