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given us an excellent compilation con- the Aristotelian doctrines to questaining all the principal facts requisite tion opinions, which bore the sanction to be known relative to this most in- of his disciples, they were content to teresting subject.

regard heat as one of the principal We shall, in the following pages, means of performing the “great work ;" endeavour to give a concise view of and though continually conversant a few of the principal phenomena of with its effects, they made no attempt heat, and to explain, in as popular a way to investigate its properties, nor to as can be done, the causes which pro- establish the laws that regulate its duce them. But before we proceed to operations ; nor would any advance this part of our subject, we would take a have been probably made in this subbrief view of the history of heat, which, ject, had not Lord Bacon, amongst his among heathen nations, from its great many other labours for the advanceimportance in nature, was considered ment of knowledge, also applied his as worthy, the patronage of parti- mind to the investigation of the nature cular deities, and Vesta and Vulcan of heat ; his “ Method of discovering were supposed to be, the former—the forms in the example of the form of divinity of heat, as a natural, the latter heat” in the Novum Organum will as an artificial agent ; and though from ever remain a perpetual monument of the continual presence and utility of his genius and penetration. In this fire in all the processes of art and short sketch he gave suggestions which nature, it would be probable that a served to place this part of physical people who deified their very vices, knowledge on its present advanced and placed among their gods the per- and eminent position ; and when we sonifications of their crimes, should consider the mass of error he had to also establish deities to represent that combat, we are astonished at that agent ; yet it seems extraordinary the acuteness of mind which enabled him opinions which were held of its efficacy to lay a foundation, which it has reas a means of purification in all their quired ages to perfect. It was not boxsacrifices, and in many of the cere ever immediately that his suggestions monials of their religion, unless we sup- were acted on; and it is only within pose their acquaintance with those our own times that investigations were nations, whose ceremonies had received entered into, which reduced the abthe sanction of divinity itself. Among struse and complicated phenomena of the philosophers of those days, the heat to the rank of the physical opinions respecting heat were as crude sciences. And it is with the great and ill-defined as most of their opinions names of Black, Watt, Davy, al relative to the different branches of Leslie, that we connect all the dis natural knowledge, and it is not sur coveries in a branch of natural knowprising that those, who would reduce ledge, which, though it has not eleall natural objects to four elementary vated its investigators to the same rank substances should suppose that heat as mental philosophers with Newton and was one of the chief of these ; some La Place, has yet given them greates of them even going so far as to assert, practical rank as the real founders of that fire was the origin or first prin- Great Britain's power and wealth. ciple of all things—that by its extinc The term heat is generally used intwo tion it produced earth or 'ashes——that significations, either to express the these ashes conceived or collected cause by which a certain sensation is moisture, whence there ensued a flood produced, or to signify the sensation of water, which again emitted air, and itself

. We say that we feel heat from that therefore fire was the elemental a fire, when we only mean that the nature of all things.*

sensation of heat is produced in us ; Such were the popular and scientific and in this sense is the word heat get notions which obtained, relative to nerally employed ; the confusion ari heat, even 'till very lately, as the al- ing from using the same word to es: chemists, who were the first investi- press two distinct ideas, has induced gators of the real constitution of many writers to make use of the wind nature were too submissive servants of caloric to express the cause of heat

• Vide History of Natural Philosophy, Bacon's Works, vol. 12.

distinct from the sensation, or repre- of paper or wool, these from their slow sent what may be deemed the matter conducting power carry away little or of heat ; but as no material confusion none of the heat of the hand; hence results from the use of the word heat, it is that different articles of clothing we shall continue to employ it, meaning seem to possess different quantities of " that cause, whatever it may be, which heat, linen always feeling colder than produces in us the peculiar sensation silken cloaths, and these colder than of heat or warmth.” Respecting the woollen, when in fact under the same nature of heat, many opinions have circumstances, they all have the same been held; the most common is, that degree of heat. heat is an imponderable substance Now if we wish to prove by experiment and consists of material particles, that this is the fact, and that heat paswhich combine with all known bodies, ses more slowly through some bodies and may, under certain circumstances, than through others, we may easily sabe separated from these and produce tisfy ourselves by very simple means ; in us the sensation of heat ; of the if we take a number of rods, of glass, other opinions—that heat is not a ma- wood, and different metals, and having terial substance, but merely a quality coated these with wax, apply beat to of matter, and that matter exhibits the ends, we shall find that the wax is heat by a vibratory motion excited in very quickly melted from the metallic its particles, or by the vibrations of a rods, very slowly from the glass, and fluid which pervades all space—it is not that a great length of time will elapse, our present purpose to enter on the before the wax is melted from the piece consideration : each has had its power- of wood, proving that heat passes ful advocates, and like the theories re- through these different substances with lative to light, there are phenomena different degrees of velocity. And we which are inexplicable by either the may remark, that in general

, the conmaterial or vibratory hypothesis se- ducting power is directly proportioned perately, and which have been trium- to the density of the substance ; the phantly referred to as crucial expe- metals being the best conductors of riments, by the supporters of each heat, next vitrified substances, then hypothesis ; and as there seems to be woods, and lastly wool, silk, and down, at present no final decision on the which are the worst conductors of merits of either, we shall, adopting the heat of all solid substances. Of all first as the most simple and most easily the metals silver is found to be the best understood, proceed to consider a few conductor of heat, consequently we of the principal facts given us in Dr. find that when boiling water is poured Lardner's most interesting volume. into a silver tea-pot, it becomes imme

If we place one hand on a piece of diately so hot that the hand can not paper or woollen cloth, and the other be placed on the outside, and it is on a piece of metal, we would be im- therefore necessary to have the handle mediately induced to believe from the made of wood, which being a bad consensation of cold produced by touching ductor of heat, no inconvenience is felt the metal that the latter was much from holding it in the hand; silver colder than the paper or wool; now spoons also when immersed in a hot lithat such is not the case must be evi- quid become immediately heated from dent if these substances have been ex the same cause, while a piece of wood posed to the same temperature under the or glass may be held without difficulty same circumstances, by which they will after having been immersed in a hot have acquired the same quantity of heat; fluid. whence then does this sensation of We extract the following interesting cold arise? why is it that our senses particulars relative to this subject from are deceived ? The answer is at once the 13th chapter of Dr. Lardner's afforded by the fact, that heat is con

treatise. veyed or conducted with different ve “ The covering of wool and feathers, locities by different substances. When which nature has provided for the infethe warm hand is placed on a piece of rior classes of animals

, has a property metal or stone, these produce immedi- of conducting heat very imperfectly ; ately in the hand the sense of cold by and hence it has the effect of keeping carrying off the heat of the hand im- the body cool in hot weather, and warm mediately, while if we touch a piece in cold weather. The heat which is

produced by powers provided in the non-conducting substances, to prevent animal economy within the body has a the waste of heat. tendency, when in a cold atmosphere, “ When wine-coolers are formed of to escape faster than it is generated ; a double casing, the space between the covering, been a non-conductor, may be filled with some non-conducting intercepts it, and keeps it confined. substance, such as powdered charcoal,

“ Man is endowed with faculties or wool; or it may be left merely filled which enable him to fabricate for him- with air." self covering similar to that with which We see, therefore, the reason why nature has provided other animals. mankind, without any knowledge of Clothes are, generally, composed of the theory of heat, have adopted partisome light non-conducting substances, cular kinds of clothing to protect themwhich protect the body from the incle- selves against the inclemency of the ment heat or cold of the external air. weather, and why the Allwise ProviIn summer, clothing keeps the body dence has varied the coverings of anicool; and in winter, warm. Woollen mals in different parts of the globe, substances are worse conductors than giving to those of the arctic regions the those composed of cotton or linen. A close and soft fur, while the inhabitants flannel shirt more effectually intercepts of the torrid districts of the globe have heat than a linen or a cotton one: and, no covering but of loose straggling whether in warm or in cold climates, hair ; the covering of each being acattain the end of clothing more effec- curately adapted to the circumstances tually.

under which they are placed. “ If we would preserve ice from We have now seen that heat enters melting, the most effectual means would into different substances, and passes be to wrap it in blankets, which would through them with different degrees of retard for a long time the approach of celerity, that metals are the best conductheat to it from any external source.

ors or carriers of heat, and that wood, “ Glass and porcelain are slow con- wool, and down are the worst Now ductors of heat; and hence my be ex- there is a circumstance attendant on the plained the fact, that vessels formed of entrance of heat into different bodies this material are frequently broken by which next deserves our attention, and suddenly introducing boiling water into is of great practical importance, as will them. If a small quantity of boiling appear from a consideration of its efwater be poured into a thick glass fects, and this is, that the shape of those tumbler, the bottom, with which the bodies into which heat enters is altered, water first comes into contact, is sud- or in other words, that heat in general denly heated, and it expands; but the expands those bodies with which it comheat, passing very slowly through it, bines. If we fill a vessel completely fails to affect the upper part of the with water and place it on the fire, we vessel, which, therefore, undergoes no find that as the water gets heated it corresponding expansion : the lower expands and overflows the vessel in parts enlarging, while the upper part which it is placed ; if we half fill a remains unaltered, a crack is produced, tight bag with air, a bladder for examwhich detaches the bottom of the ple, and hold it before the fire, the air tumbler from the upper part of it. will, on being heated, expand so much

“ In the construction of an icehouse, as to completely fill the bag ; if a bar the walls, roof, and floor should be sur of metal be fixed between two points rounded with some substance which and heated, it will either be bent out conducts heat imperfectly. A lining of shape or force away the obstacles by of straw matting, or of woollen blan- which it is confined. Now all these el kets, will answer this purpose. Air fects arise from the expansion of these being a bad conductor of heat, the bodies by heat ; which do not all er. building is sometimes constructed with pand in an equal degree, airs expanddouble walls, having a space between ing more than fluids, and fluids more them. The ice is thus surrounded by than solids ; all of which have differa wall of air as it were, which is, in a ent degrees of expansibility, metals great degree, impenetrable by heat, being expanded more by heat than previded no other source of radiation wood or glass ; or in general those be present. Furnaces intended to heat solids which are good conductors being apartments should be surrounded with more altered in their dimensions than

those which are bad conductors of heat. not having reached the stopper, it will We cannot enter minutely into the retain its former dimensions, and, convarious phenomena attendant on the sequently, will become loose in the dedilation of solids, nor consider the va canter, and may be easily withdrawn. rious apparent exceptions to the laws If the neck of the decanter be thick of expansion by heat and contraction it will be necessary to maintain the apby cold. We will content ourselves, plication of heat to it for a considerable therefore, with giving the following time to accomplish this, because heat quotations from Dr. Lardner's book, penetrates glass very slowly, it being relative to some of the consequences

one of the worst conductors. of this law:

“ Vats, tubs, barrels, and similar ves“ The result of the reasoning and sels, formed of staves of wood, are experiments explained in the present bound together by iron hoops which chapter, shows that the solid bodies by surround them. If these hoops be put which we are surrounded are continu- upon the vessel when highly heated, ally undergoing changes of bulk with and then be cooled, they will contract all the vicissitudes of temperature to so as to draw together the staves with which they are exposed. When the irresistible force. weather is cool, they shrink and con “ The same method is used to fasten tract their dimensions. On the other the tires of the wheels of carriages. hand, when the temperature of the The hoop of Iron by which the wheel is weather increases, their dimensions be- surrounded, is constructed so as exactly come enlarged ; and these effects take to fit the wheel when it is nearly redplace in different degrees in bodies hot. It this state it is placed on the composed of different materials. Thus, wheel, and then cooled ; it undergoes one metal will expand and contract a sudden contraction, and thus strongly more than another, and metals in binds the fellies upon the spokes. neral will expand and contract more

" When ornamental furniture is inthan other solids.

laid with metal, care should be taken “ If hot water be poured into a glass to provide some means for allowing the with a round bottom, the expansion metal to expand, since its dilatability produced by the heat of the water will is considerably greater than that of the cause the bottom of the glass to en wood in which it is inlaid. Inattention large, while the sides, which are not to this circumstance frequently causes heated, retain their former dimensions; the inlaid metal to start from its seat, and, consequently, if the heat be suffi- and this is particularly the case when it ciently intense, the bottom will be is inlaid upon a curved surface, such as forced from the sides, and a crack or the back of a chair. The metal, being flaw will suround that part of the glass more dilatable than the wood, becomes, by which the sides are united with the in a warm room, too large for the seat bottom. If, however, the glass be in which it is inserted, and therefore previously washed with a little warm starts out. water, so that the whole is gradually In the systems of metallic pipes by heated, and, therefore gradually ex which water is conducted to great dispanded, then the hot water may be tances for the supply of towns, and poured in without danger ; because, and other similar purposes, the changes although the bottom will expand as be- of temperature at different seasons of fore, yet the sides also enlarge, and the year cause the lengths of the pipes to whole vessel undergoes a similar change undergo such a change, that it is neof bulk.

cessary to place, at certain points along “ When the stopper of a decanter the line, pipes so constructed that they becomes fixed in so tight that it cannot are capable of sliding one within anobe removed without danger of fracture, ther, in a manner similar to the joints it may be removed by a method derived of a telescope, in order to yield to the from the property of expansion here effects of these alternate contractions explained." Let a cloth dipped in hot and delatations. If this provision were water be wrapped round the neck of not made, the series of pipes would the decanter so as to heat the glass of necessarily break by the force with the neck ; it will expand, and increase which it would contract or expand. ils dimensions; meanwhile, the heat Similar means are used for the same

purpose in all great structures of iron, panded, and the nuts screwed up as such as bridges, and are called com- before. The lamps being again with pensators.

drawn, they contracted in cooling, and “ The enormous power which solid the walls were further drawn together. bodies exert in dilating and contracting This process was continually repeated, their dimensions by change of tempe until at length the walls were restored rature, will be understood if we con- to their perpendicular position. The sider, that it must be equal to the me- gallery may still be seen with the bars chanical force necessary to produce extending across it, and binding togesimilar effects in stretching or com- ther its walls. pressing them. Thus a bar of iron There is, however, an exception to heated so as to increase its length by a this law of expansion by heat, and conquarter of an inch, would require a traction by cold, to which we would force to resist its increase of length wish to advert, from its great importequal to that which would be necessary, ance in nature, and from the frequency supposing it be maintained at the in- with which the phenomena are presented creased temperature, to reduce its to us, namely, that afforded by the freezlength by compression a quarter of an ing of water. This fluid does not inch. In like manner, a body in con- obey the law of contraction by cold, tracting by diminished temperature, after a certain limit has been arrived exerts a force exactly equal to that at ; in other words, when it has been which would be necessary to stretch it cooled to a certain point, it ceases to through the same space.

contract, and on being further cooled This principle was beautifully ap- it expands, and continues to do so until plied by M. Molard, some years ago, it has been converted into ice. This in Paris. The weight of the roof of curious faet was first ascertained by the large gallery of the Conservatoire the celebrated Florentine Academi. des Arts et Métiers pressed the sides cians, and an account of it was publishoutwards so as to endanger the building; ed in the Transactions of the Royal and it was requisite to find means by Society, in the year 1670 ; they obwhich the wall should be propped so served, that when a vessel, containing as to sustain the roof. M. Molard cor water, was placed in a mixture of snow trived the following ingenious plan for and salt (by which a great degree of the purpose. A series of strong iron cold is produced,) that the fluid erbars were carried across the building panded and rose in the neck of the from wall to wall

, passing through holes vessel; these experiments were rein the walls, and were secured by nuts peated by De Luc, who ascertained on the outside. In this state they that at about the temperature of 40° would have been sufficient to have pre- water attains its greatest density, and vented the further separation of the that any further degree of cold expands walls by the weight of the roof, but it it. The importance of this circumstance was desirable to restore the walls to will be apparent when we consider, their original state by drawing them to- that if ice were heavier than water, gether. This was effected in the fol- seas and lakes would be rendered solid lowing manner :- Alternate bars were by cold, and therefore unfit for aniheated by lamps fixed beneath them. mal life ; but by this beautiful adaptaThey expanded; and consequently the tion of nature to the wants of all her nuts, which were previously in contact creatures, neither the extremes of heat, with the walls, were no longer so. or cold of the external air can ever These nuts were then screwed up so as penetrate farther than the surface of to be again in close contact with the masses of water ; and the truth of this walls. The lamps were withdrawn, and law of nature, is also fully established the bars now allowed to cool. In cool by the fact, that during the most ining they gradually contracted, and re- tense cold the lower parts of the sea or sumed their former dimensions ; con- of lakes is never more than 40°. That sequently the nuts, pressing against the water expands during the process of walls, drew them together through a congelation has, probably, been frespace equal to that through which they quently observed by most of our reahad been screwed up. Meanwhile the ders ; water is frequently, during intermediate bars were heated and ex- severe frosts, congealed in the water

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