Chapter 9

SeeScriptores rerum Alexandri Magni(by C.W. Müller, in the Didot edition of Arrian, 1846), containing the genuine fragments and the text of the pseudo-Callisthenes, with notes and introduction; A. Westermann,De Callisthene Olynthio et Pseudo-Callisthene Commentatio(1838-1842); J. Zacher,Pseudo-Callisthenes(1867); W. Christ,Geschichte der griechischen Litteratur(1898), pp. 363, 819; article by Edward Meyer in Ersch and Gruber’sAllgemeine Encyklopädie; A. Ausfeld,Zur Kritik des griechischen Alexanderromans(Bruchsal, 1894); Plutarch,Alexander, 52-55; Arrian,Anab. iv. 10-14; Diog. Laërtius v. I; Quintus Curtius viii. 5-8; Suidass.v.See alsoAlexander The Great(ad fin.). For the Latin translations see Teuffel-Schwabe,Hist. of Roman Literature(Eng, trans.), § 399; and M. Schanz,Geschichte der römischen Litteratur, iv. i., p.43.

CALLISTO,in Greek mythology, an Arcadian nymph, daughter of Lycaon and companion of Artemis. She was transformed into a bear as a penalty for having borne to Zeus a son, Arcas, the ancestor of the Arcadians. Hera, Zeus and Artemis are all mentioned as the authors of the transformation. Arcas, when hunting, encountered the bear Callisto, and would have shot her, had not Zeus with swift wind carried up both to the skies, where he placed them as a constellation. In another version, she wasslain by Artemis. Callisto was originally only an epithet of the Arcadian Artemis herself.

See Apollodorus iii. 8; Ovid,Metam.ii. 381-530; R. Franz,De Callistus fabula(1890), which deals exhaustively with the various forms of the legend.

CALLISTRATUS,Alexandrian grammarian, flourished at the beginning of the 2nd centuryb.c.He was one of the pupils of Aristophanes of Byzantium, who were distinctively called Aristophanei. Callistratus chiefly devoted himself to the elucidation of the Greek poets; a few fragments of his commentaries have been preserved in the various collections of scholia and in Athenaeus. He was also the author of a miscellaneous work calledΣυμμικτάused by the later lexicographers, and of a treatise on courtesans (Athenaeus iii. 125 B, xiii. 591 D). He is not to be confused with Callistratus, the pupil and successor of Isocrates and author of a history of Heraclea in Pontus.

See R. Schmidt,De Callistrato Aristophaneo, appended to A. Nauck’sAristophanis Byzantii Fragmenta(1848); also C.W. Müller,Fragmenta Historicorum Graecorum, iv. p. 353 note.

CALLISTRATUS,an Athenian poet, only known as the author of a hymn in honour of Harmodius (q.v.) and Aristogeiton. This ode, which is to be found in Athenaeus (p. 695), has been beautifully translated by Thomas Moore.

CALLISTRATUS,Greek sophist and rhetorician, probably flourished in the 3rd century. He wroteΈκφράσεις, descriptions of fourteen works of art in stone or brass by distinguished artists. This little work, which is written in a dry and affected style, without any real artistic feeling, is usually edited with theΕἰκόνεςof Philostratus.

Edition by Schenkl-Reisch (Teubner series, 1902); see also C.G. Heyne,Opuscula Academica, v. pp. 196-221, with commentary on theDescriptiones; F. Jacobs,Animadversiones criticae in Callistrati statuas(1797).

CALLISTRATUSof Aphidnae, Athenian orator and general in the 4th centuryb.c.For many years, asprostates, he supported Spartan interests at Athens. On account of the refusal of the Thebans to surrender Oropus, which on his advice they had been allowed to occupy temporarily, Callistratus, despite his magnificent defence (which so impressed Demosthenes that he resolved to study oratory), was condemned to death, 361b.c.He fled to Methone in Macedonia, and on his return to Athens in 355 he was executed.

See Xenophon,Hellenica, iii. 3, vi. 2; Lycurgus,In Leocr.93.

CALLOT, JACQUES(1592-1635), French engraver, was born at Nancy in Lorraine, where his father, Jean Callot, was a herald-at-arms. He early discovered a very strong predilection for art, and at the age of twelve quitted home without his father’s consent, and set out for Rome where he intended to prosecute his studies. Being utterly destitute of funds he joined a troop of Bohemians, and arrived in their company at Florence. In this city he had the good fortune to attract the notice of a gentleman of the court, who supplied him with the means of study; but he removed in a short time to Rome, where, however, he was recognized by some relatives, who immediately compelled him to return home. Two years after this, and when only fourteen years old, he again left France contrary to the wishes of his friends, and reached Turin before he was overtaken by his elder brother, who had been despatched in quest of him. As his enthusiasm for art remained undiminished after these disappointments, he was at last allowed to accompany the duke of Lorraine’s envoy to the papal court. His first care was to study the art of design, of which in a short time he became a perfect master. Philip Thomasin instructed him in the use of the graver, which, however, he ultimately abandoned, substituting the point as better adapted for his purposes. From Rome he went to Florence, where he remained till the death of Cosimo II., the Maecenas of these times. On returning to his native country he was warmly received by the then duke of Lorraine, who admired and encouraged him. As his fame was now spread abroad in various countries of Europe, many distinguished persons gave him commissions to execute. By the Infanta Isabella, sovereign of the Low Countries, he was commissioned to engrave a design of the siege of Breda; and at the request of Louis XIII. he designed the siege of Rochelle and the attack on the Isle of Ré. When, however, in 1631 he was desired by that monarch to execute an engraving of the siege of Nancy, which he had just taken, Callot refused, saying, “I would rather cut off my thumb than do anything against the honour of my prince and of my country”; to which Louis replied that the duke of Lorraine was happy in possessing such subjects as Callot. Shortly after this he returned to his native place, from which the king failed to allure him with the offer of a handsome pension. He engraved in all about 1600 pieces, the best of which are those executed in aquafortis. No one ever possessed in a higher degree the talent for grouping a large number of figures in a small space, and of representing with two or three bold strokes the expression, action and peculiar features of each individual. Freedom, variety andnaivetécharacterize all his pieces. His Fairs, his Miseries of War, his Sieges, his Temptation of St Anthony and his Conversion of St Paul are the best-known of his plates.

See also Edouard Meaume,Recherches sur la vie de Jacques Callot(1860).

CALLOVIAN(fromCallovium, the Latinized form of Kellaways, a village not far from Chippenham in Wiltshire), in geology, the name introduced by d’Orbigny for the strata which constitute the base of the Oxfordian or lowermost stage of the Middle Oolites. The term used by d’Orbigny in 1844 was “Kellovien,” subsequently altered to “Callovien” in 1849; William Smith wrote “Kellaways” or “Kelloways Stone” towards the close of the 18th century. In England it is now usual to speak of the Kellaways Beds; these comprise (1) the Kellaways Rock, alternating clays and sands with frequent but irregular concretionary calcareous sandstones, with abundant fossils; and (2) a lower division, the Kellaways Clay, which often contains much selenite but is poor in fossils. The lithological characters are impersistent, and the sandy phase encroaches sometimes more, sometimes less, upon the true Oxford Clay. The rocks may be traced from Wiltshire into Bedfordshire, Lincolnshire and Yorkshire, where they are well exposed in the cliffs at Scarborough and Gristhorpe, at Hackness (90 ft.), Newtondale (80 ft.) and Kepwick (100 ft.). In Yorkshire, however, the Callovian rocks lie upon a somewhat higher palaeontological horizon than in Wiltshire. In England,Kepplerites calloviensisis taken as the zone fossil; other common forms areCosmoceras modiolare,C. gowerianum,Belemnites oweni,Ancyloceras calloviense,Nautilus calloviensis,Avicula ovalis,Gryphaea bilobata, &c.

On the European continent the “Callovien” stage is used in a sense that is not exactly synonymous with the English Callovian; it is employed to embrace beds that lie both higher and lower in the time-scale. Thus, the continental Callovien includes the following zones:—

Rocks of Callovian age (according to the continental classification) are widely spread in Europe, which, with the exception of numerous insular masses, was covered by the Callovian Sea. The largest of these land areas lay over Scandinavia and Finland, and extended eastward as far as the 40th meridian. In arctic regions these rocks have been discovered in Spitzbergen, Franz Josef Land, the east coast of Greenland, and Siberia. They occur in the Hebrides and Skye and in England as indicated above. In France they are well exposed on the coast of Calvados between Trouville and Dives, where the marls and clays are 200 ft. thick. In the Ardennes clays bearing pyrites and oolitic limonite are about 30 ft. thick. Around Poitiers the Callovian is 100 ft. thick, but the formation thins in the direction of the Jura.

Clays and shales with ferruginous oolites represent the Callovian of Germany; while in Russia the deposits of this age are mainly argillaceous. In North America Callovian fossils are found in California; in South America in Bolivia. In Africa they have been found in Algeria and Morocco, in Somaliland and Zanzibar, and on the west coast of Madagascar. In India they arerepresented by the shales and limestones of the Chari series of Cutch. Callovian rocks are also recorded from New Guinea and the Moluccas.

SeeJurassic; also A. de Lapparent,Traité de géologie, vol. ii. (5th ed., 1906), and H.B. Woodward, “The Jurassic Rocks of Britain,”Mem. Geol. Survey, vol. v.

(J. A. H.)

CALM,an adjective meaning peaceful, quiet; particularly used of the weather, free from wind or storm, or of the sea, opposed to rough. The word appears in Frenchcalme, through which it came into English, in Spanish, Portuguese and Italiancalma. Most authorities follow Diez (Etym. Wörterbuch der romanischen Sprachen) in tracing the origin to the Low Latincauma, an adaptation of Greekκαῦμα, burning heat,καίειν, to burn. The Portuguesecalmahas this meaning as well as that of quiet. The connexion would be heat of the day, rest during that period, so quiet, rest, peacefulness. The insertion of thel, which in English pronunciation disappears, is probably due to the Latincalor, heat, with which the word was associated.

CALMET, ANTOINE AUGUSTIN(1672-1757), French Benedictine, was born at Mesnil-la-Horgne on the 26th of February 1672. At the age of seventeen he joined the Benedictine order, and in 1698 was appointed to teach theology and philosophy at the abbey of Moyen-Moutier. He was successively prior at Lay, abbot at Nancy and of Sénones in Lorraine. He died in Paris on the 25th of October 1757. The erudition of Calmet’s exegetical writings won him a reputation that was not confined to the Roman Catholic Church, but they have failed to stand the test of modern scholarship. The most noteworthy are:—Commentaire de la Bible(Paris, 23 vols. 1707-1716), andDictionnaire historique, géographique, critique, chronologique et littéral de la Bible(Paris, 2 vols., 1720). These and numerous other works and editions of the Bible are known only to students, but as a pioneer in a branch of Biblical study which received a wide development in the 19th century, Calmet is worthy of remembrance. As a historical writer he is best known by hisHistoire ecclésiastique et civile de la Lorraine(Nancy, 1728), founded on original research and various useful works on Lorraine, of which a full list is given In Vigouroux’sDictionnaire de la Bible.

See A. Digot,Notice biographique et littéraire sur Dom Augustin Calmet(Nancy, 1860).

CALNE,a market town and municipal borough in the Chippenham parliamentary division of Wiltshire, England, 99 m. west of London by the Great Western railway. Pop. (1901) 3457. Area, 356 acres. It lies in the valley of the Calne, and is surrounded by the high table-land of Salisbury Plain and the Marlborough Downs. The church of St Mark has a nave with double aisles, and massive late Norman pillars and arches. The tower, which fell in 1628, was perhaps rebuilt by Inigo Jones. Other noteworthy buildings are a grammar school, founded by John Bentley in 1660, and the town-hall. Bacon-curing is the staple industry, and there are flour, flax and paper mills. The manufacture of broadcloth, once of great importance, is almost extinct. Calne is governed by a mayor, four aldermen and twelve councillors.

In the 10th century Calne (Canna,Kalne) was the site of a palace of the West-Saxon kings. Calne was the scene of the synod of 978 when, during the discussion of the question of celibacy, the floor suddenly gave way beneath the councillors, leaving Archbishop Dunstan alone standing upon a beam. Here also a witenagemot was summoned in 997. In the Domesday Survey Calne appears as a royal borough; it comprised forty-seven burgesses and was not assessed in hides. In 1565 the borough possessed a gild merchant, at the head of which were two gild stewards. Calne claimed to have received a charter from Stephen and a confirmation of the same from Henry III., but no record of these is extant, and the charter actually issued to the borough by James II. in 1687 apparently never came into force. The borough returned two members to parliament more or less irregularly from the first parliament of Edward I. until the Reform Bill of 1832. From this date the borough returned one member only until, by the Redistribution of Seats Act of 1885, the privilege was annulled. In 1303 Lodovicus de Bello Monte, prebendary of Salisbury, obtained a grant of a Saturday market at the manor of Calne, and a three days’ fair at the feast of St Mary Magdalene; the latter was only abandoned in the 19th century. Calne was formerly one of the chief centres of cloth manufacture in the west of England, but the industry is extinct.

CALOMEL, a drug consisting of mercurous chloride, mercury subchloride, Hg2Cl2, which occurs in nature as the mineral horn-quicksilver, found as translucent crystals belonging to the tetragonal system, with an adamantine lustre, and a dirty white grey or brownish colour. The chief localities are Idria, Obermoschel, Horowitz in Bavaria and Almaden in Spain. It was used in medicine as early as the 16th century under the namesDraco mitigatus, Manna metallorum, Aquila alba, Mercurius dulcis; later it became known as calomel, a name probably derived from the Greekκαλός, beautiful, andμέλας, black, in allusion to its blackening by ammonia, or fromκαλόςandμέλι, honey, from its sweet taste. It may be obtained by heating mercury in chlorine, or by reducing mercuric chloride (corrosive sublimate) with mercury or sulphurous acid. It is manufactured by heating a mixture of mercurous sulphate and common salt in iron retorts, and condensing the sublimed calomel in brick chambers. In the wet way it is obtained by precipitating a mercurous salt with hydrochloric acid. Calomel is a white powder which sublimes at a low red heat; it is insoluble in water, alcohol and ether. Boiling with stannous chloride solution reduces it to the metal; digestion with potassium iodide gives mercurous iodide. Nitric acid oxidizes it to mercuric nitrate, while potash or soda decomposes it into mercury and oxygen. Long continued boiling with water gives mercury and mercuric chloride; dilute hydrochloric acid or solutions of alkaline chlorides convert it into mercuric chloride on long boiling.

The molecular weight of mercurous chloride has given occasion for much discussion. E. Mitscherlich determined the vapour density to be 8.3 (air = 1), corresponding to HgCl. The supporters of the formula Hg2Cl2pointed out that dissociation into mercury and mercuric chloride would give this value, since mercury is a monatomic element. After contradictory evidence as to whether dissociation did or did not occur, it was finally shown by Victor Meyer and W. Harris (1894) that a rod moistened with potash and inserted in the vapour was coloured yellow, and so conclusively proved dissociation. A. Werner determined the molecular weights of mercurous, cuprous and silver bromides, iodides and chlorides in pyridine solution, and obtained results pointing to the formula HgCl, etc. However, the double formula, Hg2Cl2, has been completely established by H.B. Baker (Journ. Chem. Soc., 1900, 77, p. 646) by vapour density determinations of the absolutely dry substance.

Calomel possesses certain special properties and uses in medicine which are dealt with here as a supplement to the general discussion of the pharmacology and therapeutics of mercury (q.v.). Calomel exerts remote actions in the form of mercuric chloride. The specific value of mercurous chloride is that it exerts the valuable properties of mercuric chloride in the safest and least irritant manner, as the active salt is continuously and freshly generated in small quantities. Its pharmacopeial preparations are the “Black wash,” in which calomel and lime react to form mercurous oxide, a pill still known as “Plummer’s pill” and an ointment. Externally the salt has not any particular advantage over other mercurial compounds, despite the existence of the official ointment. Internally the salt is given in doses—for an adult of from one-half to five grains. It is an admirable aperient, acting especially on the upper part of the intestinal canal, and causing a slight increase of intestinal secretion. The stimulant action occurring high up in the canal (duodenum and jejunum), it is well to follow a dose of calomel with a saline purgative a few hours afterwards. The special value of the drug as an aperient depends on its antiseptic power and its stimulation of the liver. The stools are dark green, containing calomel, mercuric sulphide and bile which, owing to the antiseptic action, has not been decomposed. The salt is often used in the treatment of syphilis, but is probably less useful than certain other mercurial compounds. It is also employed forfumigation; the patient sits naked with a blanket over him, on a cane-bottomed chair, under which twenty grains of calomel are volatilized by a spirit-lamp; in about twenty minutes the calomel is effectually absorbed by the skin.

CALONNE, CHARLES ALEXANDRE DE(1734-1803), French statesman, was born at Douai of a good family. He entered the profession of the law, and became in succession advocate to the general council of Artois,procureurto the parlement of Douai, master of requests, then intendant of Metz (1768) and of Lille (1774). He seems to have been a man of great business capacity, gay and careless in temperament, and thoroughly unscrupulous in political action. In the terrible crisis of affairs preceding the French Revolution, when minister after minister tried in vain to replenish the exhausted royal treasury and was dismissed for want of success, Calonne was summoned to take the general control of affairs. He assumed office on the 3rd of November 1783. He owed the position to Vergennes, who for three years and a half continued to support him; but the king was not well disposed towards him, and, according to the testimony of the Austrian ambassador, his reputation with the public was extremely poor. In taking office he found “600 millions to pay and neither money nor credit.” At first he attempted to develop the latter, and to carry on the government by means of loans in such a way as to maintain public confidence in its solvency. In October 1785 he recoined the gold coinage, and he developed thecaisse d’ escompte. But these measures failing, he proposed to the king the suppression of internal customs, duties and the taxation of the property of nobles and clergy. Turgot and Necker had attempted these reforms, and Calonne attributed their failure to the malevolent criticism of the parlements. Therefore he had an assembly of “notables” called together in January 1787. Before it he exposed the deficit in the treasury, and proposed the establishment of asubvention territoriale, which should be levied on all property without distinction. This suppression of privileges was badly received by the privileged notables. Calonne, angered, printed his reports and so alienated the court. Louis XVI. dismissed him on the 8th of April 1787 and exiled him to Lorraine. The joy was general in Paris, where Calonne, accused of wishing to augment the imposts, was known as “Monsieur Deficit.” In reality his audacious plan of reforms, which Necker took up later, might have saved the monarchy had it been firmly seconded by the king. Calonne soon afterwards passed over to England, and during his residence there kept up a polemical correspondence with Necker on the finances. In 1789, when the states-general were about to assemble, he crossed over to Flanders in the hope of being allowed to offer himself for election, but he was sternly forbidden to enter France. In revenge he joined theémigréparty at Coblenz, wrote in their favour, and expended nearly all the fortune brought him by his wife, a wealthy widow. In 1802, having again taken up his abode in London, he received permission from Napoleon to return to France. He died on the 30th of October 1802, about a month after his arrival in his native country.

See Ch. Gomel,Les Causes financières de la Révolution(Paris, 1893); R. Stourm,Les Finances de l‘ancien régime et de la Révolution(2 vols., Paris, 1885); Susane,La Tactique financière de Calonne, with bibliography (Paris, 1902).

CALORESCENCE(from the Lat.calor, heat), a term invented by John Tyndall to describe an optical phenomenon, the essential feature of which is the conversion of rays belonging to the dark infra-red portion of the spectrum into the more refrangible visible rays,i.e.heat rays into rays of light. Such a transformation had not previously been observed, although the converse phenomenon,i.e.the conversion of short waves of light into longer or less refrangible waves, had been shown by Sir G.G. Stokes to occur in fluorescent bodies. Tyndall’s experiments, however, were carried out on quite different lines, and have nothing to do with fluorescence (q.v.). His method was to sift out the long dark waves which are associated with the short visible waves constituting the light of the sun or of the electric arc and to concentrate the former to a focus. If the eye was placed at the focus, no sensation of light was observed, although small pieces of charcoal or blackened platinum foil were immediately raised to incandescence, thus giving rise to visible rays.

The experiment is more easily carried out with the electric light than with sunlight, as the former contains a smaller proportion of visible rays. According to Tyndall, 90% of the radiation from the electric arc is non-luminous. The arc being struck in the usual way between two carbons, a concave mirror, placed close behind it, caused a large part of the radiation to be directed through an aperture in the camera and concentrated to a focus outside. In front of the aperture were placed a plate of transparent rock-salt, and a flat cell of thin glass containing a solution of iodine in carbon bisulphide. Both rock-salt and carbon bisulphide are extremely transparent to the luminous and also to the infra-red rays The iodine in the solution, however, has the property of absorbing the luminous rays, while transmitting the infra-red rays copiously, so that in sufficient thicknesses the solution appears nearly black. Owing to the inflammable nature of carbon bisulphide, the plate of rock-salt was found to be hardly a sufficient protection, and Tyndall surrounded the iodine cell with an annular vessel through which cold water was made to flow. Any small body which was a good absorber of dark rays was rapidly heated to redness when placed at the focus. Platinized platinum (platinum foil upon which a thin film of platinum had been deposited electrolytically) and charcoal were rendered incandescent, black paper and matches immediately inflamed, ordinary brown paper pierced and burned, while thin white blotting-paper, owing to its transparency to the invisible rays, was scarcely tinged. A simpler arrangement, also employed by Tyndall, is to cause the rays to be reflected outwards parallel to one another, and to concentrate them by means of a small flask, containing the iodine solution and used as a lens, placed some distance from the camera. The rock-salt and cold water circulation can then be dispensed with.

Since the rays used by Tyndall in these experiments are similar to those emitted by a heated body which is not hot enough to be luminous, it might be thought that the radiation, say from a hot kettle, could be concentrated to a focus and employed to render a small body luminous. It would, however, be impossible by such means to raise the receiving body to a higher temperature than the source of radiation. For it is easy to see that if, by means of lenses of rock-salt or mirrors, we focused all or nearly all the rays from a small surface on to another surface of equal area, this would not raise the temperature of the second surface above that of the first; and we could not obtain a greater concentration of rays from a large heated surface, since we could not have all parts of the surface simultaneously in focus. The desired result could be obtained if it were possible, by reflection or otherwise, to cause two different rays to unite without loss and pursue a common path. Such a result must be regarded as impossible of attainment, as it would imply the possibility of heat passing from one body to another at a higher temperature, contrary to the second law of thermodynamics (q.v.). Tyndall used the dark rays from a luminous source, which are emitted in a highly concentrated form, so that it was possible to obtain a high temperature, which was, however, much lower than that of the source.

A full account of Tyndall’s experiments will be found in hisHeat, a Mode of Motion.

(J. R. C.)

CALORIMETRY, the scientific name for the measurement of quantities of heat (Lat.calor), to be distinguished from thermometry, which signifies the measurement of temperature. A calorimeter is any piece of apparatus in which heat is measured. This distinction of meaning is purely a matter of convention, but it is very rigidly observed. Quantities of heat may be measured indirectly in a variety of ways in terms of the different effects of heat on material substances. The most important of these effects are (a) rise of temperature, (b) change of state, (c) transformation of energy.

§ 1. The rise of temperature of a body, when heat is imparted to it, is found to be in general nearly proportional to the quantity of heat added. Thethermal capacityof a body is measured by the quantity of heat required to raise its temperature one degree, and is necessarily proportional to the mass of the body for bodiesof the same substance under similar conditions. Thespecific heatof a substance is sometimes defined as the thermal capacity of unit mass, but more often as the ratio of the thermal capacity of unit mass of the substance to that of unit mass of water at some standard temperature. The two definitions are identical, provided that the thermal capacity of unit mass of water, at a standard temperature, is taken as the unit of heat. But the specific heat of water is often stated in terms of other units. In any case it is necessary to specify the temperature, and sometimes also the pressure, since the specific heat of a substance generally depends to some extent on the external conditions. The methods of measurement, founded on rise of temperature, may be classed asthermometric methods,since they depend on the observation of change of temperature with a thermometer. The most familiar of these are the method of mixture and the method of cooling.

§ 2. TheMethod of Mixtureconsists in imparting the quantity of heat to be measured to a known mass of water, or some other standard substance, contained in a vessel or calorimeter of known thermal capacity, and in observing the rise of temperature produced, from which data the quantity of heat may be found as explained in all elementary text-books. This method is the most generally convenient and most readily applicable of calorimetric methods, but it is not always the most accurate, for various reasons. Some heat is generally lost in transferring the heated body to the calorimeter; this loss may be minimized by performing the transference rapidly, but it cannot be accurately calculated or eliminated. Some heat is lost when the calorimeter is raised above the temperature of its enclosure, and before the final temperature is reached. This can be roughly estimated by observing the rate of change of temperature before and after the experiment, and assuming that the loss of heat is directly proportional to the duration of the experiment and to the average excess of temperature. It can be minimized by making the mixing as rapid as possible, and by using a large calorimeter, so that the excess of temperature is always small. The latter method was generally adopted by J.P. Joule, but the rise of temperature is then difficult to measure with accuracy, since it is necessarily reduced in nearly the same proportion as the correction. There is, however, the advantage that the correction is rendered much less uncertain by this procedure, since the assumption that the loss of heat is proportional to the temperature-excess is only true for small differences of temperature. Rumford proposed to eliminate this correction by starting with the initial temperature of the calorimeter as much below that of its enclosure as the final temperature was expected to be above the same limit. This method has been very generally recommended, but it is really bad, because, although it diminishes the absolute magnitude of the correction, it greatly increases the uncertainty of it and therefore the probable error of the result. The coefficient of heating of a calorimeter when it is below the temperature of its surroundings is seldom, if ever, the same as the coefficient of cooling at the higher temperature, since the convection currents, which do most of the heating or cooling, are rarely symmetrical in the two cases, and moreover, the duration of the two stages is seldom the same. In any case, it is desirable to diminish the loss of heat as much as possible by polishing the exterior of the calorimeter to diminish radiation, and by suspending it by non-conducting supports, inside a polished case, to protect it from draughts. It is also very important to keep the surrounding conditions as constant as possible throughout the experiment. This may be secured by using a large water-bath to surround the apparatus, but in experiments of long duration it is necessary to use an accurate temperature regulator. The method of lagging the calorimeter with cotton-wool or other non-conductors, which is often recommended, diminishes the loss of heat considerably, but renders it very uncertain and variable, and should never be used in work of precision. The bad conductors take so long to reach a steady state that the rate of loss of heat at any moment depends on the past history more than on the temperature of the calorimeter at the moment. A more serious objection to the use of lagging of this kind is the danger of its absorbing moisture. The least trace of damp in the lagging, or of moisture condensed on the surface of the calorimeter, may produce serious loss of heat by evaporation. This is another objection to Rumford’s method of cooling the calorimeter below the surrounding temperature before starting. Among minor difficulties of the method may be mentioned the uncertainty of the thermal capacity of the calorimeter and stirrer, and of the immersed portion of the thermometer. This is generally calculated by assuming values for the specific heats of the materials obtained by experiment between 100° C. and 20° C. Since the specific heats of most metals increase rapidly with rise of temperature, the values so obtained are generally too high. It is best to make this correction as small as possible by using a large calorimeter, so that the mass of water is large in proportion to that of metal. Analogous difficulties arise in the application of other calorimetric methods. The accuracy of the work in each case depends principally on the skill and ingenuity of the experimentalist in devising methods of eliminating the various sources of error. The form of apparatus usually adopted for the method of mixtures is that of Regnault with slight modifications, and figures and descriptions are given in all the text-books. Among special methods which have been subsequently developed there are two which deserve mention as differing in principle from the common type. These are (1) the constant temperature method, (2) the continuous flow method.Fig. 1.Fig. 2.Theconstant temperature method of mixtureswas proposed by N. Hesehus (Jour. Phys., 1888, vii. p. 489). Cold water at a known temperature is added to the calorimeter, immediately after dropping in the heated substance, at such a rate as to keep the temperature of the calorimeter constant, thus eliminating the corrections for the water equivalent of the calorimeter and the external loss of heat. The calorimeter is surrounded by an air-jacket connected to a petroleum gauge which indicates any small change of temperature in the calorimeter, and enables the manipulator to adjust the supply of cold water to compensate it. The apparatus as arranged by F.A. Waterman is shown in fig. 1 (Physical Review,1896, iv. p. 161). A is the calorimetric tube, B the air-jacket and L the gauge. H is an electric heater for raising the body to a suitable temperature, which can swing into place directly over the calorimeter. W is a conical can containing water cooled by ice I nearly to 0°, which is swung over the calorimeter as soon as the hot body has been introduced and the heater removed. The cold water flow is regulated by a tap S with a long handle O, and its temperature is taken by a delicate thermometer with its bulb at G. The method is interesting, but the manipulations and observations involved are more troublesome than with the ordinary type of calorimeter, and it may be doubted whether any advantage is gained in accuracy.Thecontinuous flow methodis specially applicable to the important case of calorific value of gaseous fuel, where a large quantity of heat is continuously generated at a nearly uniform rate by combustion. Fig. 2 illustrates a recent type of gas calorimeter devised by C.V. Boys (Proc. R.S.,1906, A. 77, p. 122). The heated products of combustion from the burner B impinge on a metal box H, through which water is circulating, and then pass downwards and outwards through a spiral cooler which reduces them practically to the atmospheric temperature. A steady stream of water enters the apparatus by the inflow thermometer O,flows through the spiral coolers N and M, and finally through the box H, where it is well mixed before passing the outflow thermometer P. As soon as a steady state is reached, the difference of temperature between the outflow and inflow thermometers, multiplied by the current of water in grammes per minute gives the heat per minute supplied by combustion. The gas current is simultaneously observed by a suitable meter, which, with subsidiary corrections for pressure, temperature, &c., gives the necessary data for deducing calorific value.A continuous flow calorimeter has been used by the writer for measuring quantities of heat conveyed by conduction (seeConduction of Heat), and also for determining the variation of the specific heat of water. In the latter case two steady currents of water at different temperatures, say 0° and 100° are passed through an equalizer, and the resulting temperature measured without mixing the currents, which are then separately determined by weighing. This is a very good method of comparing the mean specific heats over two ranges of temperature such as 0-50, and 50-100, or 0-20 and 20-40, but it is not so suitable as the electric method described below for obtaining the actual specific heat at any point of the range.

Theconstant temperature method of mixtureswas proposed by N. Hesehus (Jour. Phys., 1888, vii. p. 489). Cold water at a known temperature is added to the calorimeter, immediately after dropping in the heated substance, at such a rate as to keep the temperature of the calorimeter constant, thus eliminating the corrections for the water equivalent of the calorimeter and the external loss of heat. The calorimeter is surrounded by an air-jacket connected to a petroleum gauge which indicates any small change of temperature in the calorimeter, and enables the manipulator to adjust the supply of cold water to compensate it. The apparatus as arranged by F.A. Waterman is shown in fig. 1 (Physical Review,1896, iv. p. 161). A is the calorimetric tube, B the air-jacket and L the gauge. H is an electric heater for raising the body to a suitable temperature, which can swing into place directly over the calorimeter. W is a conical can containing water cooled by ice I nearly to 0°, which is swung over the calorimeter as soon as the hot body has been introduced and the heater removed. The cold water flow is regulated by a tap S with a long handle O, and its temperature is taken by a delicate thermometer with its bulb at G. The method is interesting, but the manipulations and observations involved are more troublesome than with the ordinary type of calorimeter, and it may be doubted whether any advantage is gained in accuracy.

Thecontinuous flow methodis specially applicable to the important case of calorific value of gaseous fuel, where a large quantity of heat is continuously generated at a nearly uniform rate by combustion. Fig. 2 illustrates a recent type of gas calorimeter devised by C.V. Boys (Proc. R.S.,1906, A. 77, p. 122). The heated products of combustion from the burner B impinge on a metal box H, through which water is circulating, and then pass downwards and outwards through a spiral cooler which reduces them practically to the atmospheric temperature. A steady stream of water enters the apparatus by the inflow thermometer O,flows through the spiral coolers N and M, and finally through the box H, where it is well mixed before passing the outflow thermometer P. As soon as a steady state is reached, the difference of temperature between the outflow and inflow thermometers, multiplied by the current of water in grammes per minute gives the heat per minute supplied by combustion. The gas current is simultaneously observed by a suitable meter, which, with subsidiary corrections for pressure, temperature, &c., gives the necessary data for deducing calorific value.

A continuous flow calorimeter has been used by the writer for measuring quantities of heat conveyed by conduction (seeConduction of Heat), and also for determining the variation of the specific heat of water. In the latter case two steady currents of water at different temperatures, say 0° and 100° are passed through an equalizer, and the resulting temperature measured without mixing the currents, which are then separately determined by weighing. This is a very good method of comparing the mean specific heats over two ranges of temperature such as 0-50, and 50-100, or 0-20 and 20-40, but it is not so suitable as the electric method described below for obtaining the actual specific heat at any point of the range.

§ 3.Method of Cooling.—A common example of this method is the determination of the specific heat of a liquid by filling a small calorimeter with the liquid, raising it to a convenient temperature, and then setting it to cool in an enclosure at a steady temperature, and observing the time taken to fall through a given range when the conditions have become fairly steady. The same calorimeter is afterwards filled with a known liquid, such as water, and the time of cooling is observed through the same range of temperature, in the same enclosure, under the same conditions. The ratio of the times of cooling is equal to the ratio of the thermal capacities of the calorimeter and its contents in the two cases. The advantage of the method is that there is no transference or mixture; the defect is that the whole measurement depends on the assumption that the rate of loss of heat is the same in the two cases, and that any variation in the conditions, or uncertainty in the rate of loss, produces its full effect in the result, whereas in the previous case it would only affect a small correction. Other sources of uncertainty are, that the rate of loss of heat generally depends to some extent on the rate of fall of temperature, and that it is difficult to take accurate observations on a rapidly falling thermometer. As the method is usually practised, the calorimeter is made very small, and the surface is highly polished to diminish radiation. It is better to use a fairly large calorimeter to diminish the rate of cooling and the uncertainty of the correction for the water equivalent. The surface of the calorimeter and the enclosure should be permanently blackened so as to increase the loss of heat by radiation as much as possible, as compared with the losses by convection and conduction, which are less regular. For accurate work it is essential that the liquid in the calorimeter should be continuously stirred, and also in the enclosure, the lid of which must be water-jacketed, and kept at the same steady temperature as the sides. When all these precautions are taken, the method loses most of the simplicity which is its chief advantage. It cannot be satisfactorily applied to the case of solids or powders, and is much less generally useful than the method of mixture.

§ 4.Method of Fusion.—The methods depending on change of state are theoretically the simplest, since they do not necessarily involve any reference to thermometry, and the corrections for external loss of heat and for the thermal capacity of the containing vessels can be completely eliminated. They nevertheless present peculiar difficulties and limitations, which render their practical application more troublesome and more uncertain than is usually supposed. They depend on the experimental fact that the quantity of heat required to produce a given change of state (e.g.to convert one gramme of ice at 0° C. into water at 0° C., or one gramme of water at 100° C. into steam at 100° C.) is always the same, and that there need be no change of temperature during the process. The difficulties arise in connexion with the determination of the quantities of ice melted or steam condensed, and in measuring the latent heat of fusion or vaporization in terms of other units for the comparison of observations. The earlier forms of ice-calorimeter, those of Black, and of Laplace and Lavoisier, were useless for work of precision, on account of the impossibility of accurately estimating the quantity of water left adhering to the ice in each case. This difficulty was overcome by the invention of the Bunsen calorimeter, in which the quantity of ice melted is measured by observing the diminution of volume, but the successful employment of this instrument requires considerable skill in manipulation. The sheath of ice surrounding the bulb must be sufficiently continuous to prevent escape of heat, but it must not be so solid as to produce risk of strain. The ideal condition is difficult to secure. In the practical use of the instrument it is not necessary to know both the latent heat of fusion of ice and the change of volume which occurs on melting; it is sufficient to determine the change of volume per calorie, or the quantity of mercury which is drawn into the bulb of the apparatus per unit of heat added. This can be determined by a direct calibration, by inserting a known quantity of water at a known temperature and observing the contraction, or weighing the mercury drawn into the apparatus. In order to be independent of the accuracy of the thermometer employed for observing the initial temperature of the water introduced, it has been usual to employ water at 100° C., adopting as unit of heat the “mean calorie,” which is one-hundredth part of the heat given up by one gramme of water in cooling from 100° to 0° C. The weight of mercury corresponding to the mean calorie has been determined with considerable care by a number of observers well skilled in the use of the instrument. The following are some of their results:—Bunsen, 15.41 mgm.; Velten, 15.47 mgm.; Zakrevski, 15.57 mgm.; Staub, 15.26 mgm. The explanation of these discrepancies in the fundamental constant is not at all clear, but they may be taken as an illustration of the difficulties of manipulation attending the use of this instrument, to which reference has already been made. It is not possible to deduce a more satisfactory value from the latent heat and the change of density, because these constants are very difficult to determine. The following are some of the values deduced by well-known experimentalists for the latent heat of fusion:—Regnault, 79.06 to 79.24 calories, corrected by Person to 79.43; Person, 79.99 calories; Hess, 80.34 calories; Bunsen, 80.025 calories. Regnault, Person and Hess employed the method of mixture which is probably the most accurate for the purpose. Person and Hess avoided the error of water sticking to the ice by using dry ice at various temperatures below 0° C., and determining the specific heat of ice as well as the latent heat of fusion. These discrepancies might, no doubt, be partly explained by differences in the units employed, which are somewhat uncertain, as the specific heat of water changes rapidly in the neighbourhood of 0° C; but making all due allowance for this, it remains evident that the method of ice-calorimetry, in spite of its theoretical simplicity, presents grave difficulties in its practical application.

One of the chief difficulties in the practical use of the Bunsen calorimeter is the continued and often irregular movement of the mercury column due to slight differences of temperature, or pressure between the ice in the calorimeter and the ice bath in which it is immersed. C.V. Boys (Phil. Mag., 1887, vol. 24, p. 214) showed that these effects could be very greatly reduced by surrounding the calorimeter with an outer tube, so that the ice inside was separated from the ice outside by an air space which greatly reduces the free passage of heat. The present writer has found that very good results may be obtained by enclosing the calorimeter in a vacuum jacket (as illustrated in fig. 3), which practically eliminates conduction and convection. If the vacuum jacket is silvered inside, radiation also is reduced to such an extent that, if the vacuum is really good, the external ice bath may be dispensed with for the majority of purposes. If the inner bulb is filled with mercury instead of water and ice, the same arrangement answers admirably as a Favre and Silbermann calorimeter, for measuring small quantities of heat by the expansion of the mercury.The question has been raised by E.L. Nichols (Phys. Rev.vol. 8, January 1899) whether there may not be different modifications of ice with different densities, and different values of the latent heat of fusion. He found for natural pond-ice a density 0.9179 and for artificial ice 0.9161. J. Vincent (Phil. Trans.A. 198, p. 463) also found a density .9160 for artificial ice, which is probably very nearlycorrect. If such variations of density exist, they may introduce some uncertainty in the absolute values of results obtained with the ice calorimeter, and may account for some of the discrepancies above enumerated.

The question has been raised by E.L. Nichols (Phys. Rev.vol. 8, January 1899) whether there may not be different modifications of ice with different densities, and different values of the latent heat of fusion. He found for natural pond-ice a density 0.9179 and for artificial ice 0.9161. J. Vincent (Phil. Trans.A. 198, p. 463) also found a density .9160 for artificial ice, which is probably very nearlycorrect. If such variations of density exist, they may introduce some uncertainty in the absolute values of results obtained with the ice calorimeter, and may account for some of the discrepancies above enumerated.

§ 5. TheMethod of Condensationwas first successfully applied by J. Joly in the construction of his steam calorimeter, a full description of which will be found in text-books. The body to be tested is placed in a special scale-pan, suspended by a fine wire from the arm of a balance inside an enclosure which can be filled with steam at atmospheric pressure. The temperature of the enclosure is carefully observed before admitting steam. The weight of steam condensed on the body gives a means of calculating the quantity of heat required to raise it from the atmospheric temperature up to 100° C. in terms of the latent heat of vaporization of steam at 100° C. There can be no appreciable gain or loss of heat by radiation, if the admission of the steam is sufficiently rapid, since the walls of the enclosure are maintained at 100° C., very nearly. The thermal capacity of the scale-pan, &c., can be determined by a separate experiment, or, still better, eliminated by the differential method of counterpoising with an exactly similar arrangement on the other arm of the balance. The method requires very delicate weighing, as one calorie corresponds to less than two milligrammes of steam condensed; but the successful application of the method to the very difficult problem of measuring the specific heat of a gas at constant volume, shows that these and other difficulties have been very skilfully overcome. The application of the method appears to be practically limited to the measurements of specific heat between the atmospheric temperature and 100° C. The results depend on the value assumed for the latent heat of steam, which Joly takes as 536.7 calories, following Regnault. Joly has himself determined the mean specific heat of water between 12° and 100° C. by this method, in terms of the latent heat of steam as above given, and finds the result .9952. Assuming that the mean specific heat of water between 12° and 100° is really 1.0011 in terms of the calorie at 20° C. (see table, p. 66), the value of the latent heat of steam at 100° C., as determined by Joly, would be 540.2 in terms of the same unit. The calorie employed by Regnault is to some extent uncertain, but the difference is hardly beyond the probable errors of experiment, since it appears from the results of recent experiments that Regnault made an error of the same order in his determination of the specific heat of water at 100° C.

§ 6.Energy Methods.—The third general method of calorimetry, that based on the transformation of some other kind of energy into the form of heat, rests on the general principle of the conservation of energy, and on the experimental fact that all other forms of energy are readily and completely convertible into the form of heat. It is therefore often possible to measure quantities of heat indirectly, by measuring the energy in some other form and then converting it into heat. In addition to its great theoretical interest, this method possesses the advantage of being frequently the most accurate in practical application, since energy can be more accurately measured in other forms than in that of heat. The two most important varieties of the method are (a) mechanical, and (b) electrical. These methods have reached their highest development in connexion with the determination of the mechanical equivalent of heat, but they may be applied with great advantage in connexion with other problems, such as the measurement of the variation of specific heat, or of latent heats of fusion or vaporization.

§ 7.Mechanical Equivalent of Heat.—The phrase “mechanical equivalent of heat” is somewhat vague, but has been sanctioned by long usage. It is generally employed to denote the number of units of mechanical work or energy which, when completely converted into heat without loss, would be required to produce one heat unit. The numerical value of the mechanical equivalent necessarily depends on the particular units of heat and work employed in the comparison. The British engineer prefers to state results in terms of foot-pounds of work in any convenient latitude per pound-degree-Fahrenheit of heat. The continental engineer prefers kilogrammetres per kilogramme-degree-centigrade. For scientific use the C.G.S. system of expression in ergs per gramme-degree-centigrade, or “calorie,” is the most appropriate, as being independent of the value of gravity. A more convenient unit of work or energy, in practice, on account of the smallness of the erg, is thejoule,which is equal to 10.7 ergs, or onewatt-secondof electrical energy. On account of its practical convenience, and its close relation to the international electrical units, thejoulehas been recommended by the British Association for adoption as the absolute unit of heat. Other convenient practical units of the same kind would be thewatt-hour,3600 joules, which is of the same order of magnitude as the kilo-calorie, and thekilowatt-hour,which is the ordinary commercial unit of electrical energy.

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