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degree, and then remains stationary: this may be which previously adhered to the glass, and that rectified by elevating the scale of the instrument mercury is utterly incapable of absorbing either the required quantity. The other takes place at air or moisture. The extraordinary way in which every change of temperature; it is small and air and water is held as it were in a film over scarcely perceptible, with small changes of tem- glass is insisted upon, and reference made to perature, but by considerable changes becomes many authors in proof of it. The following, howvery evident and important.
ever, are more interesting, as being some of the Singular consequences sometimes result from facts he advances to prove that the mercury never the influence of these changes. If two liquids be contains either of these substances. Fill a barotaken of different temperatures, a greater differ meter tube and boil it very carefully; then preence will be found between them, by trying the pare a kind of funnel made of a small capillary hot fluid, and then the cold fluid by the same iube, which will reach through the mercury in the thermometer, than what will appear to exist by barometer tube to the closed end, and is enlarged trying the cold fluid first. Again, if a new ther- at top; let it be recently made, so as to be dry, mometer be graduated by an old one preserved and introduce it into the barometer tube; preas a standard, although it may be made to agree pare some mercury by agitating it in a bottle with it, yet, after a while, the two will not ac with water and air, then drying its surface with cord; and if two old thermometers be taken that bibulous paper, and afterwards passing it through do
agree, and the one be heated whilst the other paper cones three or four times into dry vessels; remains unused, they will no longer indicate the pour a little of this mercury into the funnel tube, same temperatures.
and with a horse-hair or fine wire remove the air, The reason now becomes evident, why alcohol so that the column may be continuous; then thermometers are so much less affected in this pour in so much of this prepared mercury ag manner than those filled with mercury. Alcohol will fully displace the mercury that was boiled expands several times more than mercury, so that in the tube ; afterwards remove the funnel tube, an instrument constructed with it having a tube and put the barometer to its proper use. It will of the same diameter, and degrees of the same be found to stand exactly at the same height as size, will require a bulb several times less than if before in the same circumstances; and if the .mercury had been used. Hence, as the elevation mercury be now boiled in the tube, none of those is in proportion to the capacity of the bulb, in- bubbles will appear which arose on the first dependent of the liquid it contains, the alcohol boiling; care being taken throughout that the thermometer will exhibit a much smaller effect inner surface of the tube has not been exposed than the mercurial instrument.
to the air. MM. A. de la Rive and F. Marcet have also Perhaps an easier mode of making the same investigated the elevation of the mercury in ther- experiment is to make the barometer terminate at mometers, which is due to the cause pointed out top in a bulb, which will hold more mercury than by Mr. Flaugergues, namely, the continued pres- is required to fill the tube : then when it is sure of the air on its external surface: and by boiled it need only be placed upright in a basin of opening the top of the thermometer, by submit common mercury, and, when inclined, the merting the instrument to condensed or rare atmo- cury will enter and replace that which was boiled spheres, and by comparison with thermometers in the instrument; the results will be as above. otherwise constructed, have abundantly proved An experiment proving the same thing may be the effect due to this power. These philosophers made still more easily thus: fill a mercurial therhad occasion also to remark some curious effects mometer and boil it well; then heat it till nearly due to the absorption and evolution of heat, by all the mercury is expelled, but preserve its open the expansion and condensation of gases, which extremity under common mercury: the latter however we cannot at this time further attend to, metal will enter as the instrument cools, and than by copying the conclusions at the end of the behave in every respect as the well-boiled mermemoir.
1. That atmospheric pressure exerts an influence If a bulb of a thermometer be suddenly on the bulk of thermometer bulbs. 2. That in squeezed between the finger and the thumb, the experiments, where this effect may influence the mercury will rise in the stem several degrees, and results, it is better to use thermometers open at will again sink as quickly after the pressure is the top. 3. That certainly cold is produced in removed. To prevent any derangement from making a vacuum by the air-pump, but in communication of heat, the hand may be covered smaller quantity than was supposed. 4. That when with a thick glove. This is a very important gases enter an exhausted vessel, there is at first fact, and it may be shown in a less exceptionable a production of cold, and then of heat. 5. That way :-let a mercurial thermometer, with a large various modifications may render the cold pro- bulb and a long stem, be first held upright, and duced at the moment of the entrance of air into then immediately inverted; between these two a vacuum more intense.
positions the column of mercury will descend Sig. Bellani has undertaken a series of experi- through a visible space: thus proving that a vaments, to determine whether the air or vapor, the riable pressure in the atmosphere, or mercury, last portions of which are found to remain so ob- will produce anomalies in the thermometer. stinately in barometers and thermometers, is in Mr. Breguet's thermometer consists of slips troduced with the mercury, or is a portion of that of two metals, unequally expanded by heat, which originally occupied the tube before the in- twisted into a spiral : to the extremity of the troduction of the metal. The conclusion he spiral is fixed an index, which moves round a comes to is, that it is always a portion of that graduated circle, pointing out the temperature.
It is obvious that, when the spiral is heated, the on the short arm of a lever index, the free exindex will move in one direction, and in another tremity of which moves along a graduated arc. when the spiral is cooled, because it will twist or The instrument is originally adjusted on a good untwist itself according to the changes of tempe- mercurial thermometer; and the movements of the rature to which it is subjected. The two metals arm are registered by two fine wires, which are employed are silver and platinum; and in order pushed before it, and left at the maximum deviato render the extreme points more fixed, and to tion to the right or left of the last observed poprevent sudden starts, a slip of gold, the expan- sition or temperature. sibility of which is intermediate between that of M. Fourier has invented a new instrument silver and platinum, is soldered between these which he calls a thermometer of contact. It contwo metals. This thermometer is more delicate · sists of a conical vessel constructed of very thin than any mercurial thermometer whatever. It is iron, with the exception of the bottom, which is even more delicate than an air thermometer. made of thin pliable skin; it is filled with merThis spiral thermometer, and a mercurial one, cury and has a thermometer, the bulb of which were placed together under the receiver of an air is immersed entirely in the mercury, and the pump. The temperature at the time of the ex- scale has degrees of such magnitude that they periment was 66.2°. The mercurial thermometer, may be divided into tenths. The skin must be when the air was pumped out, sunk 3.6°; but preserved perfectly clean and never be overthe spiral thermometer fell 41.4°, and descended heated; it is better than any other similarly flexto 24.8° Fahrenheit.
ible substance, because of its superior conducting The differential thermometer, invented by pro- power. This instrument is to be accompanied fessor Leslie, consists of two tubes, each termi- by a support consisting of a block of marble ; nating in a small bulb of similar dimensions; a and any substance operated upon is to be in small portion of dark-colored fluid, formed of sheets or reduced to thin plates. When an exsulphuric acid tinged with carmine, having pre- periment is to be made, the sheet, cloth, or thin viously been introduced into one of the balls. plate, is to be placed upon the marble, both The instrument is then fixed on a stand, and fur- being at the temperature of the room; the coninished with a graduated scale. When the co cal vessel, with its contents, is to be heated on a lumn is equally pressed in opposite directions, stove or other hot body, until about 46° or 47° C.; the fluid will point at zero, and whatever heat and then being removed, at the moment it has may be applied to the whole instrument, provided fallen to 45°, it is to be placed on the substance both bulbs receive it in an equal degree, the be tried; the time when it arrives at 40° fluid must remain at rest. But, if the one ball be exactly noted by a watch, and then the temreceives the slightest excess of temperature, the perature noted minute by minute for five minutes. air which it contains will be proportionally ex If the experiment be repeated with the same subpanded, and the column will be depressed with a stance on another part of the inarble, exactly the force equal to the difference between the tempe- same results will be obtained, provided the temrature of the two balls.
perature of the place has not changed. If the A self-registering thermometer is a most im- experiments are to be made on rigid plates, then portant instrument, and, as such, must not be these are not to be placed directly upon the passed unnoticed. It is employed to indicate marble, but upon a mercurial cushion, made by the extreme changes that occur in the tempera- confining mercury under a surface of skin. ture of the air. Dr. Rutherford employed two If the substance first tried be replaced by anthermometers. The one which marks the mini- other, and then the fall of temperature in a given mum is filled with alcohol; and the other, time be noted, the variation will be found very which indicates the maximum, is filled with sensible, however slight the difference between quicksilver; and they are both attached to the the substances; the addition of a single sheet of same frame, or, what is still better, affixed to se the finest paper makes a great difference in the parate frames, placed nearly horizontal, or rather effect. The slightest difference in the nature of elevated about five degrees, to prevent the sepa- the stuff is iminediately indicated. If a piece of ration of the thread of liquid. The tubes have linen cloth be replaced by flannel, or by woollen bores from the twenty-fifth to the fifteenth part of cloth, or a thin piece of woollen cloth by a thick an inch wide, and include a minute tapered or piece, not only are the differences produced very conical piece of ivory, or of white or blue evident, but they can be obtained over and over enamel, about half an inch long. This mark, again with the utmost constancy, care being having in either thermometer its base turned taken that the pressure of the mercury upon the towards the bulbs, is drawn to the lowest point skin, and therefore upon the substance, be the by the alcohol, which again freely passes it; but same in all cases. it is always pushed forward to the highest limit The same instrument also indicates the heat by the inercury, which afterwards leaves it. of contact of bodies. In such cases, after being
Mr. Crichton has contrived a self-registering heated as before-mentioned, it is to be placed thermometer, somewhat similar to that of M. on a thick mass of the substance to be tried, Breguet ; consisting of two oblong slips of steel and the fall of temperature in a given time and zinc, firmly fixed together by their faces; so noted as before: striking effects were thus obthat the greater expansion or contraction of the tained. Deing first applied to iron at the temzinc over those of ihe steel, by the same varia- perature of 8° C., and then upon a mass of stone, tions of temperature, causes a flexure of the com the difference at the end of the second minute pound bar. As this is secured to a board at one was 5o. The differences are much greater when end, the whole flexure is exercised at the other, iron is compared with brick or wood. Although
the conducting powers thus obtained for different bulbs near to each other, and to what is to be substances are only approximations, yet there are the top of the instrument, or the instrument may many bodies, as bricks, stones, wood, clothing, be reversed; the ball may be considered the top, &c., for which these are quite sufficient.
and the other extremity being turned round, may Another still more delicate method of ascer- have the two bulbs blown on it so as to resemble taining the conducting power of bodies is then a common form of the barometer; this being described, but it is also more difficult. Two done, alcohol is to be introduced, until not only vessels are used; the lower one is maintained at the ball and tube, but the lower bulb, and part of a constant temperature, as 100° C.; upon that the upper are filled with it. is placed the substance to be tried, and upon In these thermometers, one object was to avoid that again the upper vessel. The lower part of the injurious effect occasioned by the adhesion of the upper vessel is enclosed, and constituites the the surface of the fluid in the tube with the glass; bulb of an air thermometer; the upper part is the surface of the fluid is therefore not regarded retained at the temperature of ice; the air there as any indication of the state of the instrument; fore in the thermometer is cooled by the ice and it is always in the upper bulb, and is very little warmed by the lower heated vessel; the latter altered by any alteration of temperature; but a producing an effect greater or smaller according point is taken in the column of alcohol in the to the nature of the substance between it and the tube, by which to make observations, and this air-vessel; the temperature of the air and the in- point is marked by a small cylinder of mercury; dication upon the scale connected with it soon and in addition to the advantage thus obtained, becomes permanent, and, as it is higher or lower, of perfect freedom of motion, the column which, indicates the greater or less conducting power of before from its minuteness was with difficulty the interposed substance. When the experi- visible, becomes readily distinguishable at the ments are carefully made they accord with those necessary point. The mercury is readily introof the former instrument, but are more delicate. duced into the tube of the instrument by warming
By means of these instruments M. Fourier it, and then introducing is extremity into the was able to ascertain that many substances when metal on cooling; it passes first into the bulbs, put together, conducted heat differently, accord- and may then be placed in any required part of ing to the order in which they were placed. what is to be the scale, and this being done the Two pieces of cloth being put between the in- instrument is to be closed and graduated. strument and the marble, the order of substances In this way thermometers have been made so traversed by the heat was skin, cloth-cloth, delicately that with a ball of three lines and a marble. After observing the effect a thin plate half in diameter each degree, (of Reaumur) has of copper was placed between the cloth and the been ten and twelve inches in length, which exmarble; the fall of temperature was then slower tension allows of a division to the four hundredth than before; the copper was then placed between and even the six hundredth part of a degree, the pieces of cloth, and the cooling was as if no without affecting the accuracy of the instrument. copper were present; then placing the copper In graduating it the principal points may be beneath the skin of the instrument and above taken from a mercurial thermometer, and the the cloth, so that the order was skin, copper, division into equal parts adopted for the others. cloth, cloth, marble, the temperature diminished Landriani enumerates some of the advantages more rapidly than no copper had been there: this instrument has over common mercurial therthus the interposition of the metal facilitated the mometers. It is more readily constructed, the transmission of heat from the skin to the cloth, adhesion of the mercury to the glass being obbut diminished the transmission from the cloth viated, and even the adhesion of the surface of to the marble.
the alcohol being of no consequence. Its maThe chevalier Landriani has described in the terial, the alcohol, has more fluidity and expanGiornale di Fisica, &c., a method contrived and sibility than mercury. In mercurial instruments adopted by himself in the construction of very the weight of the metal endangers the bulb, whicli delicate thermometers ; and, from his experience, being necessarily thiu, is liable to accidents in a he is induced to consider instruments made in much greater degree than when filled with alcohis way much superior to the common mercurial hol. Another important defect to which merthermometer.
curial thermometers are liable, and from which The form of the instrument is nearly that of these are very nearly free, is the expansion of the the common thermometer; but the tube is of ex- ball at the extremity by the weight of the column treme fineness, a quarter of a grain of mercury of mercury in the tube ; and this column varying occupying in it a length of three, four, and even with the temperature, and its pressure by posifive inches. In order to blow á ball at the end tion, errors of a very changeable nature are inof such a tube, it is found necessary to attach a troduced. Thus, wiih a mercurial thermometer condensing syringe to it, the elastic gum bottle having a ball of four or five lines in diameter, not being sufficient for the purpose; and in and degrees of four or five lines in length, the forcing in the air when the end of the glass has temperature indicated is not the same in a verbeen heated to produce the ball, great care must tical and in a horizontal position. be taken that no. moisture or oil enter the tube, Landriani proposes also the use of his instruas the smallest particle completely closes up its ment in determining fractions of degrees which
cannot be observed by the common thermometer. The ball and tube are then filled with alcohol This is done by graduating the instrument into in the usual manner; and, after this is done, the degrees according to common thermometers, but bore of the tube is to be expanded into two small not affixing numbers to them; and then by dis
placing the mercury from part to part, the scale the lowest degrees of heat which are commonly may be made to commence at any given degree. observed even in cold climates, but they by no If the mercury be made to descend into the ball means reach to those degrees of heat which are of the instrument, or to rise into the bulb, and very familiar to us. The mercurial thermometer the instrument be placed horizontally, the tem- extends no farther than to 600 of Fahrenheit's perature of the whole may then be brought to scale, the heat of boiling mercury; but we are any required point; and that done, by placing sure that the heat of solid bodies, when heated the thermometer vertically with the ball upwards to ignition, or till they emit light, far exceeds the or downwards as required, the mercury is made heat of boiling mercury. To remedy this defect, to enter the tube, and passes over degrees gra- Sir Isaac Newton, whose genius overcame those duated upwards or downwards from the tem- obstacles which ordinary minds could not apperature to which the whole instrument was proach, attempted by an ingenious experiment brought.
to extend the scale to any degree required. M. Landriani, in a succeeding number of the Having heated a mass of iron red hot, and exGiornale di Fisica, has proposed these thermo- posed it to the cold air, he observed the time meters to be used in meteorological observations which elapsed till it became cold, or of the as self-registering thermometers, and they appear same temperature with the air; and, when the very applicable to this purpose. They are to be heat so far decreased that he could apply some constructed as before described, except that be- known measure (as a thermometer) to it, he obsides the cylinder of mercury, which is the indi- served the degrees of heat lost in given times, cator of temperature, there is to be another portion and thence drew the general conclusion, that the of mercury within, either the ball or the first quantities of heat lost in given small spaces are bulb, as the instrument is to measure the extreme always proportional to the heat remaining in the point of heat or of cold.
body, reckoning the heat to be the excess by The use is as follows:-Supposing it put by, which it is warmer than the ambient air. So that the indicating cylinder of mercury will, of course, taking the number of minutes which it took to be somewhere in the stem, and the other portion cool after it came to a determined point in an of metal should be in the ball; if it be required arithmetical progression, the decrements of the to mark the lowest degree of cold during the night, heat of iron would be continually proportional. it is to be placed upright with the ball upwards, Having by this proportion found out the decreand the point where the indicator stands noted; ments of heat in a given time, after it came to a the mercury in the ball will rest just over the known point, it was easy, by carrying upwards orifice of the tube, and will enter it on any the same proportion to the beginning of its cooldescent of the column beneath; if the tempera- ing, to determine the greatest heat which the ture diminishes, however, that column will body had acquired. This proportion of Sir Isaac's ascend, the spirit in the ball contracting; but, was found by Dr. Martine to be somewhat inacwhenever it begins to expand again, the mercury curate. The heat of a cooling body does not dein the ball will descend, dividing the alcohol crease exactly in proportion to that which the above and below it. When the instrument is body retains. As the result of many observanext observed, therefore, nothing more is required tions, he found that two kinds of proportion to ascertain the extreme cold of the night than to took place, an arithmetical as well as the geoinemark the numbers of degrees between the two trical proportion which Sir Isaac Newton had cylinders of mercury, and these, subtracted from adopted ; namely, that the decrements of heat the numbers of degrees between the indicator, were partly proportional to the times (that is, and the ball or the mercury at the first observa- that quantities of heat are lost in equal times), as tion, give the degrees of cold.
well as partly in proportion to the remaining In ascertaining the extreme heat, M. Landriani heat; and that if these two are added together the proposed to use another therinometer with the rule will be sufficiently accurate. By the geoball downward, when the first bulb will become metrical proportion which Sir Isaac Newton the receptacle for the registering portion of mer- adopted, he discovered the heat of metals red hot cury, and the difference between the two columns or in fusion. of alcohol included between the indicator and the The method above-mentioned, so successfully bulb at the first observation, and the indicator pursued by Sir Isaac, was sufficient to form a and registering mercury at the second, will give scale of high degrees of heat, but was not conthe extreme heat of the instrument between the venient for practical purposes. Accordingly the two observations.
ingenious Mr. Josiah Wedgwood, who is well It would be easy, however, to make one in- known for his great improvement in the art of strument answer both purposes, and one which pottery, applied himself in order to discover a M. Landriani depicts is very fit for them; the thermometer which might be easily managed. ball is above, and the tube is bent just above the After many experiments recorded in the Philobulbs, so that they shall also stand perpendicu- sophical Transactions, but which it is unneceslarly and rising upwards from the tube. If then sary to detail here, he invented a thermometer a small portion of mercury be appropriated to which marks with much precision the different the ball, and another to the first bulb, the former degrees of ignition, from a dull red heat visible will indicate the lowest temperature in the ab- in the dark to the heat of an air furnace. This sence of the observer, and the latter the highest, thermometer is extremely simple. It consists of the indicator of course always being present. two rulers fixed upon a smooth flat plate, a little
The thermometers above described are very farther asunder at the one end than the other, limited in their extent; they indeed point out to leaving an open longitudinal space between them,
Small pieces of alum and clay mixed together
Fahrenheit's are made of such a size as just to enter at the
scale. wide end; they are then heated in the fire along Brandy boils
190 with the body whose heat we wish to determine. Alcohol boils
174 The fire, according to the degree of heat it con- Serum of blood and white of eggs tains, diminishes or contracts the earthy body, so
156 that, when applied to the wide end of the gage; Heat of the air near Senegal some
Bees' wax melts.
142 it will slide on towards the narrow end, less or more according to the degree of heat to which it times
111 has been exposed.
Hens hatch eggs about
108 Mr. Wedgwood found that ten cwt. of the Heat of birds from
103 to 111 porcelain clay of Cornwall required all the earth Heat of domestic quadrupeds from 100 to 103 that was afforded by five cwt. of alum. But, as
Heat of the human boly
92 to 99 the clay or alum differs in quality, the proportion Heat of a swarm of bees
97 will also differ. There can now, however, be no
Heat of the ocean under the equator 80 difficulty in making thermometers of this kind, Butter melts
74 as common clay answers the purpose very well, Sulphuric acid of the specific graand alum earth can easily be procured. Those vity of 1780 freezes at
45 who wish to see a more particular account of Oil of olives begins to congeal 43 this subject may peruse Mr. Wedgwood's papers Heat of hedgehogs and marmots in the Philosophical Transactions for 1782, 1784, in a torpid state
39} and 1786. As Mr. Wedgwood's thermometer Water Freizes and snow melts 32 begins at the lowest degree of ignition, and Fah- Milk freezes
28 renheit's goes no higher than the boiling point of Common vinegar freezes mercury, Mr. Wedgwood continued to fill up Human blood freezes
25 the interval of the scale by using a piece of silver Strong wines freeze instead of his common thermometer pieces ; and A mixture of one part of alcohol in this way he has found that 130° of Fah and three parts of water freezes 7 renheit are equal to one of his. He has ac- A mixture of snow and salt freezes 0 to 4 cordingly, by observing this proportion, continued Brandy, or a mixture of equal parts Fahrenheit's scale to the top of his own. We of alcohol and water freezes are now, therefore, enabled to give a scale of Spirit of wine in Reaumur's therheat from the highest ree of heat produced mometer froze at Torneo. -34 by an air furnace to the greatest degree of cold MERCURY FREEZES
-39 or 40 hitherto known, which was produced at Hudson's Cold produced by Mr. Macnab at Bay in December 1784, by a mixture of vitriolic Hudson's Bay by a mixture of acid and snow.
Of the remarkable degrees be sulphuric acid and snow . -69 tween these extreme points we shall lay before our readers
THERMOPYLE, in ancient geography, a Fahren- Wedg.
narrow pass or defile, between the Sinus Maliacus A Scale.
on the east, and steep mountains, reaching to
Oeta, made dreadful by impassable woods, on
scale. scale. Extremity of Wedgwood's scale 32277° 240°
the west; leading from Thessaly to Locris and Greatest heat of his small air-fur
Bæotia. These mountains divide Greece in the 21877 160
middle, in the same manner as the Appennines do Cast iron melts
Italy; forming one continued ridge from LeuGreatest heat of a common smith's
cate on the west to the sea on the east, with
thickets and rocks interspersed; so that forge 17327 125
persons Welding heat of iron, greatest 13427 95
even prepared for travelling, much less an army least
encumbered with baggage, cannot easily find a
12777 90 Fine gold melts
In the valley verging 5237 32 Fine silver melts
towards the Sinus Maliacus the road is only
4717 Swedish copper melts
sixty paces broad; the only military way for an Brass melts
army to pass if not obstructed by an enemy; Heat by which enamel colors are
and therefore the place is called Pylæ, and by burnt on
others, on account of its hot water, Thermopylæ. Red-heat fully visible in day-light 1077 0
It is famous for the brave stand made by LeoRed-heat fully visible in the dark 947
nidas and 300 Spartans against the whole army
1 MERCURY BOILS, also linseed and
of Persia; and also for the Amphyctiones, the other expressed oils
common council or states-general of Greece, Oil of turpentine boils
assembling there twice a year, in spring and au
tumn. Sulphuric acid boils
546 Lead melts
THER'MOSCOPE, n. s. Fr. thermoscope ; Bismuth melts
Gr. θερμος and σκοπεω. An instrument by which Tin melts.
the degrees of heat are discovered ; a ihermoSulphur melts
meter. Nitrous acid boils
By the trial of the thermoscope, fishes have more Cows' milk boils
heat than the element which they swim in. WATER BOILS 212
Arbuthnot on Aliments.