For the definitions of the derived dynamical units and the investigation of their dependence on the fundamental units. the reader may refer to the article on MECHANICS.

From what has been said it will appear that the whole difficulty in fixing upon a system of dynamical units lies in the determination of the fundamental units of length, mass, and time in such a manner that their constancy can be relied upon. The unit of mass offers very little difficulty in this respect. Long experience has taught us which are the most permanent of the varieties of matter we have at command. We have good reason to believe that a piece of platinum or an alloy of platinum and iridium nay be exposed to pure air at ordinary temperatures for an indefinite time without any increase or diminution of its mass whatever. Such a piece of metal may therefore with propriety be chosen as a national standard of mass, the absolute constancy of the quantity of matter constituting it being accepted on definition, as we are unable to test it by any standard in which we have more confidence than we have in itself. The British and French national standards of mass are of platinum, but the new standards recently constructed in Paris consist of an alloy of platinum and iridium.

The determination of a unit of length is not so simple as that of the unit of mass. In this case, as in the preceding, we avail ourselves of the properties of a material standard, but we know that however indestructible the standard itself may be its dimensions depend upon the pressure to which it is exposed, its temperature, and in some cases upon other accidents, such as the magnetic force in the neighbourhood, &c. Hence the only course open to us is to determine as far as possible all the causes of variation in the length of our standard, and carefully to define its condition with respect to these variables, so that it shall be a standard only under the circumstances thus defined. Having thus defined the condition of the material standard with respect to all the variables upon which we know its length to depend, we must consider the absolute constancy of its length at all times and places to be a matter of definition until we have discovered other causes which affect it. It has been proposed that the wave length in vacuo of a particular kind of light, as for instance that corresponding to one of the sodium lines, should be taken as the unit of length, and its period as the unit of time. These units are probably more constant than those afforded by any material standards or vibrating springs which we can construct; but a belief in their absolute constancy implies complete confidence in the constancy of the properties of the interstellar medium, and of the sodium molecule.

The determination of a satisfactory means of measuring time seems to offer greater difficulties than the measurement of mess or of space, though the difficulties are of the same character as those we have just considered. The great difficulty consists in defining what is meant by the equality of two intervals of time which do not commence simultaneously. Remembering that it is upon the properties of matter alone that we can rely for assistance, we might construct a spring and define as equal lapses of time those intervals during which this spring executes the same number of vibrations, the temperature, &c., being kept constant. But if we were to construct a number of such springs, though a perfect agreement might obtain between them at first, we should find after a considerable period that the measurements of time derived from different springs did not agree, while our knowledge is insufficient to enable us to apply to each the corrections necessary to lead us to a consistent result. Now there may be no reason why we should prefer one spring above all the others, and thus it appears that a definition of equal intervals of time based upon the behaviour of any single

spring is too arbitrary to be satisfactory. If, however, we found a large number of springs, constructed of different materials and differently affected by temperature and other known causes of variation, continue to give perfectly consistent results, the theory of probability would lead us to place a high value upon the measure of time thus afforded. Now, we have stated that our highest conception of the measurement of time is derived from the dynamical principle expressed in the first law of motion, but when we come to apply this it is impossible to determine a priori whether in the case of two given bodies there is no stress acting between them or between one of them and some third object. Consequently, the only course open to us is to examine the motion of a large number of material systems, making such corrections for the action of stresses which we know to be in operation as our theoretical dynamics will enable us to determine; and, if after this we find that several independent systems afford the salne measurement of time, while those systems which lead to a different result disagree also among themselves, we must accept the measurement of time afforded by the first set as the true measure, and attribute the discrepancies manifested by the other systems to some unknown stresses, which it should be our subsequent business to discover.

Work. The contemplation of a stress, together with a relative displacement of theportions of matter between which it acts, introduces us to the conception of work. If we consider a stress, together with the distance through which the solicited bodies are capable of moving relative to one another in obedience to the stress, the object of our contemplation is the work which may be done under the given conditions of the system, and this we call energy. The subject of which natural philosophy treats is the transformation of energy, which in all its phases takes place in accordance with two great principles, known respectively as the principles of the conservation and the dissipation of energy. Of these two principles the former rests upon a much higher scientific basis than the latter. In order to lose our faith in the principle of the conservation of energy we must give up our belief in the fundamental principles of dynamics expressed in the laws of motion; but as regards the dissipation of energy we can say little more than that all the operations of nature with which we are acquainted take place in accordance with this principle. Clerk Maxwell has, however, shown that it is possible to subvert the principle of the dissipation of energy by the simple exercise of a sufficiently high order of intelligence. For the statement and discussion of these two principles see ENERGY.

It is the work of the natural philosopher to explain the operations of nature in accordance with the principles of dynamics, and we consider that we understand any pheno.menon when we have shown it to consist of a motion of matter and determined the character of this motion. Thus it is that dynamics forms the foundation of every branch of natural philosophy, and a thorough appreciation of the principles of conservation and dissipation of energy is the only safe guide in physical investigations. (W. G.)

DYNAMITE (Sivapus, strength), the name applied to various explosive preparations containing nitroglycerin. The first practical application of nitroglycerin, discovered by Sobrero in 1847, was made by Alfred Nobel, who in 1863 used gunpowder soaked with it for blasting. In 1864 he found that it could be exploded by the initiative detonation of fulminating materials; and in 1867, owing to the uncertainty and danger attending its employment, he conceived the idea of mixing it with some solid and absorbent inert substance. The siliceous infusorial earth called in Germany Kieselguhr proved to be well adapted for this purpose, since it took up as much as three times its weight of nitroglycerin without becoming more than damp to the

touch. The mixture of earth and nitroglycerin, to which was added a little alkaline material to neutralize any acid that might be set free by the latter, was termed by Nobel dynamite. Ignited in the open air, dynamite burns slowly, but it is as readily exploded as nitroglycerin itself by means of a detonating fuze; and, though not equal in bursting or breaking power to uncombined nitroglycerin, on accouut of the absorption by its inert constituents of part of the heat developed by the exploding shock, it is greatly superior to gunpowder, instead of which or gun-cotton it is employed in blasting coal and stone, removing piles, felling trees, and clearing stumps from forest-land. It may also be used with advantage for the destruction of cannon and for breaking up large iron castings (see Compt. rend., lxxii. 770). For filling bore-holes its pasty consistency renders it a very convenient material.

In continuous masses dynamite transmits detonation at the rate of from 19,500 to 21,600 feet a second. Confinement is not requisite for its explosion, and it can be used in damp situations without to any great extent impairing its action. It explodes if heated in a closed brass case, also on sharp percussion when placed between two metallic surfaces; it should not, therefore, be kept in hermetically sealed receptacles of metal or other very solid material. At a low temperature dynamite loses its tendency to explode by detonation. Another defect is its liability to part with a portion of its nitroglycerin, especially when in contact with porous substances, such as the paper of cartridges and wrappers (see Guyot, Compt. rend., lxxii. 688). MM. Girard, Millot, and Vogt have shown (Moniteur scientifique, xiii. 58) that for the manufacture of dynamite the best absorbents are kaolin, tripoli, alumina, and sugar; the last, like alum, the material employed in Mr Horsley's preparation, has the advantage of being separable from associated nitroglycerin by solution in water. Dynamite as made by M. P. Champion consisted of 20 to 25 parts of nitroglycerin with 75 to 80 parts of finely pulverized burnt clay from glass works (Monit. scient., xiii. 91); and in some explosives sold as dynamite a mixture of sawdust and chalk is substituted for siliceous substances.

See F. A. Abel, On Recent Investigations and Applications of Explosive Agents, 1871; J. Trauzl, Die Dynamite, ihre Eigenschaf ten und Gebrauchsweise, Berlin, 1876.

DYNAMOMETER (dívaμis, strength, and μérpov, a measure), an instrument for measuring force exerted by men, animals, and machines. One of the simplest forms, namely, that devised by the mechanician Graham, and improved by Desaguliers, was essentially a steel-yard in which the position of the weight on the longer arm indicated the force exerted on the shorter in order to produce equilibrium. The dynamometer invented by Leroy of the French Academy consisted of a metallic tube 10 to 12 inches long, in which was a spiral spring with an attached graduated rod terminat ing above in a globe. Pressure being applied to the globe, the rod sank into the tube, and thus marked the force employed in compressing the spring. M. Regnier's dynamometer (see Journ. de l'Ecole Polytechnique, tom. ii.) consists of an elliptical steel spring having fixed to one of its arms a semicircular graduated brass plate with central index, and to the other a small lever, which, acting on the index, shows the amount of force exerted in effecting a greater or less approximation of the arms to each other. In a similar instrument contrived by M. Poncelet, the springs are hinged together at the extremities, and separated from each other in proportion to the tension brought to bear upon them. A dynamometer for therapeutical purposes, invented by Dr Hamilton of Long Island College Hospital, consists of an india-rubber bulb filled with coloured water, into which dips a tube closed at the upper end. Pressure being applied to the bulb, some of the water is forced up

into the tube, the graduations upon which show the amount of pressure upon the air within it which is exerted by the water. By the dynamometer of Colonel Morin a curve is drawn, the area of which represents the product of the force exerted into the space through which it acts, or, in other words, the quantity of work performed in a given time. Details with respect to Morin's, Watt's, and other dynamometers will be found in vol. i. of Laboulaye's Dictionnaire des Arts et Manufactures.

DYRRACHIUM. See Durazzo.

DYSART, a seaport town and royal and parliamentary 'burgh of Scotland, in the county of Fife, nine miles northeast of Burntisland, with a station on the North British Railway. It consists mainly of three narrow streets with a square in the centre, and on the whole has rather a dull and deserted appearance. In the High Street there are a number of antique houses with inscriptions and dates; and towards the south side of the town there are remains of an ancient chapel. Besides the old parish church with its tower, there are six places of worship, an old town-house, a mechanics' institute, and a combiuation poorhouse. The harbour is tolerably good, and there is a wet dock attached. The staple industry is the manufacture of linens and ticks; but flax-spinning and ship-building are also carried on, and there is a large export of coal. To the west of the town is Dysart House, the residence of the earl of Rosslyn. As a parliamentary borough Dysart is a member of the Kirkcaldy district. The population of the town in 1871 was 2476.

Dysart is mentioned as early as 874 at the time of a Danish invasion. Its name is said to be a corruption of the Latin descrtum, a desert, applied to a cave on the sea-shore which was occupied about 440 by St Serf or Sanctus Servanus, to whom at a later date the church was dedicated. From James V. the town received the rights of a royal burgh. In the 15th and 16th centuries it was the

seat of a great manufacture of salt, and besides dealing in this article with Holland and other countries, it had a large general trade. For several months in 1559 it was the headquarters of the Lords of meetings of the synod of Fife known in ecclesiastical history as the the Congregation, and in 1607 it was the scene of those remarkable Three Synods of Dysart. William Murray, a native of the town, was made earl of Dysart either by Charles I. or Charles 11., and his eldest daughter afterwards assumed the title of countess, and transmitted the dignity to her descendants by the earl of Lauderdale, her second husband.

DYSENTERY (from the prefix dvs, and evтepov, the intestine), also called Bloody Flux, an infectious disease with a local lesion in the form of inflammation and ulceration of the lower portion of the bowels.

Although at one time a common disease in Great Britain, dysentery is now very rarely met with there, and is for the most part confined to warm countries, where it is the cause of a large amount of mortality.

Dysentery in a sporadic form may occur anywhere, but this variety of the disease is believed to depend on a different cause from that to which it is due where it prevails endemically or spreads as an epidemic; for, while isolated cases appear capable of being excited by irritating causes which act locally on the alimentary canal, and may thus be developed out of an ordinary intestinal catarrh, the dysentery of tropical climates is generally regarded as owing its origin to a specific poison of the nature of a miasm or germ, somewhat analogous to that which is believed to be the cause of malignant cholera. How, and under what circumstances, the dysentery_poison is generated is still a matter of uncertainty. The frequent association of dysentery with intermittent fever has long been remarked, and has led to the belief on the part of many in a malarial origin for this disease. It is, however, doubtful whether any necessary relationship can be established between them (although a malarial form of dysentery is a well marked variety of the disease), since dysentery may be found prevailing where no evidence of malaria can be detected. At the same time

certain characters of climate and soil are known to favour the increase and propagation of dysentery. Long continued high temperature of the air and ground, such as exists in the tropics, together with a soil of swampy character, are the conditions generally present where dysentery prevails endemically, and where it is propagated as an epidemic these factors are seldom absent. Among other causes well recognized as favouring the spread of epidemic dysentery are impure air and water, improper and insufficient food, unripe fruit, excessive indulgence in alcoholic liquors, and exposure to chills in warm weather, all or many of which have been often found connected with the propagation of dysentery among large bodies of people, as in the case of armies, where also the disease has been frequently associated with outbreaks of scurvy.

The contagiousness of epidemic dysentery is generally admitted, and it is probable that in this disease as in cholera the vehicle of its transmission is contained in the matter discharged from the bowels of those affected.

Dysentery manifests itself with varying degrees of intensity, but in well-marked cases the following are the chief symptoms. The attack is commonly preceded by certain premonitory indications in the form of general illness, loss of appetite, and some amount of diarrhoea, which gradually increases in severity, and is accompanied with griping pains in the abdomen (tormina). The discharges from the bowels succeed each other with great frequency, and the painful feeling of pressure downwards (tenesmus) becomes so intense that the patient is constantly desiring to defecate. The matters passed from the towels, which at first resemble those of ordinary diarrhoea, soon change their character, becoming scanty, mucous or slimy, and subsequently mixed with, or consisting wholly of, blood, along with shreds of exudation thrown off from the mucous membrane of the intestine. The evacuations possess a peculiarly offensive odour characteristic of the disease. Although the constitutional disturbance is at first comparatively slight, it increases with the advance of the disease, and febrile symptoms come on attended with urgent thirst and scanty and painful flow of urine. Along with this the nervous depression is very marked, and the state of prostration to which the patient is reduced can scarcely be exceeded. Should no improvement occur death may take place in from- one to three weeks, either from repeated losses of blood, or from gradual exhaustion consequent on the continuance of the symptoms, in which case the discharges from the bowels become more offensive and are passed involuntarily.

When, on the other hand, the disease is checked, the signs of improvement are shown in the cessation of the pain, in the evacuations being less frequent and more natural, and in relief from the state of extreme depression. Convalescence is, however, generally slow, and recovery may be imperfect the disease continuing in a chronic form, which may exist for a variable length of time, giving rise to much suffering, and not unfrequently leading to an ultimately fatal result.

Several varieties of dysentery are described in which the symptoms are modified by the association of the disease with other morbid conditions. Thus the form known as Malarial Dysentery is complicated with febrile attacks of an intermittent character, and is frequently attended with hepatic, splenic, and renal affections; while it is most successfully treated by remedies which are of value in malarial diseases, such as quinine. Again, in Scorbutic Dysentery the attack is accompanied with the great prostration characteristic of scorbutus, and also with dangerous hemorrhage. Malignant Dysentery is the term applied to those cases where all the symptoms are present in great intensity, and progress rapidly to a fatal termination. Such cases are

often attended with gangrene and sloughing of the mucous membrane of the affected portion of the bowel.

The dysentery poison appears to exert its effects upon the glandular structures of the large intestine, particularly in its lower part. In the milder forms of the disease there is simply a congested or inflamed condition of the mucous membrane, with perhaps some inflammatory exudation on its surface, which is passed off by the discharges from the bowels. But in the more severe forms ulceration of the mucous membrane takes place. Commencing in and around the solitary glands of the large intestine in the form of exudations, these ulcers, small at first, enlarge and run into each other, till a large portion of the bowel may be implicated in the ulcerative process. Should the disease be arrested these ulcers may heal entirely, but occasionally they remain, causing more or less disorganization of the coats of the intestines, as is often found in chronic dysentery. Sometimes, though rarely, the ulcers perforate the intestines, causing rapidly fatal inflammation of the peritoneum, or they may erode a blood vessel and produce violent hemorrhage. Even where they undergo healing they may cause such a stricture of the calibre of the intestinal canal as to give rise to the symptoms of obstruction which ultimately prove fatal.

The occurrence of abscess of the liver in connection with attacks of dysentery is frequently observed. It has been ascribed to the passage of morbid material from the diseased intestine into the liver, but by many high authorities is regarded more as a coincidence, depending upon the same climatic causes as those which predispose to the dysentery.

Treatment.-Where the disease is endemie or is prevailing epidemically, it is of great importance to use all preventive measures, and for this purpose the avoidance of all causes likely to precipitate an attack is to be enjoined. Exposure to cold after heat, the use of unripe fruit, and intemperance in eating and drinking should be forbidden; and the utmost care taken as to the quality of the food and drinking water. In houses or hospitals where cases of the disease are under treatment, disinfectants should be freely employed, and the evacuations of the patients removed as speedily as possible. In the milder varieties of this complaint, such as those occurring sporadically, and where the symptoms are probably due to matters in the bowels setting up the dysenteric irritation, the employment of diaphoretic medicines is to be recommended, and the administration of such a laxative as castor-oil, to which a small quantity of laudanum has been added, will often, by removing the source of the mischief, arrest the attack. In the severer forms of the disease, those, namely, occurring in warm climates, the remedy most to be relied on is ipecacuanha. This drug, which has long been known as possessing special efficacy in dysentery (and was originally introduced into this country from Peru as the radix anti-dysenterica), has proved of signal value in the treatment of the disease in India, and, as shown by Dr Maclean, has diminished the mortality to a remarkable extent. It is administered in full doses of 25-30 grains of the powder, which are repeated in from six to ten hours, gradually lessening the quantity; the effect observable is a diminution in the pain, and in the frequency and offensive character of the stools, along with the accession of profuse perspiration and quiet sleep. Hot opiate fomentations applied to the abdomen are of use in relieving the tenesmus. Ice may be freely taken to allay thirst. The diet should be light, consisting of soups and farinaceous food. In malarial dysentery quinine is the most successful remedy, ipecacuanha being generally found to be unsuitable; while in scorbutic dysentery the treatment must bear reference to the depraved condition of tho general health characteristic of scorbutus. In this form VII.

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have been founded largely on the observations of Dr Beaumont in the celebrated case of Alexis St Martin, are only valuable within certain limits when applied to the treatment of dyspepsia. It must be borne in mind that idiosyncrasy often plays an important part in digestion, some persons being unable to partake without injury of substances which are generally regarded as wholesome and digestible. Difficulty, too, is often experienced in dealing with dyspeptics from their aversion to, or want of appetite for, those forms of diet which appear most suitable for them. Experience has shown that in this complaint no particular kind of food is absolutely to be relied on, but that in general the best diet is one of a mixed animal and vegetable kind simply but well cooked. The partaking of many dishes, of highly seasoned or salted meats, raw vegetables, newly baked bread, pastry, and confectionery, are all well known common causes of dyspepsia, and should be avoided. When even the simple diet usually taken is found to disagree, it may be necessary to change it temporarily for a still lighter form, such as a milk diet, and that even in very moderate quantity.

General hygienic measures are highly important, since whatever improves the state of the health will have a favourable influence on digestion. Hence regular exercise in the open air, early rising, and the cold bath are to be strongly recommended.

The medicinal remedies for dyspepsia are exceedingly numerous, and a few only of them can be mentioned. Attacks brought on by errors in diet are generally relieved by small doses of rhubarb and bismuth, and by the use of small quantities of light and bland food. In chronic dyspepsia the treatment must depend on the cause of the disorder, so far as that can be ascertained. When the dyspepsia is of the atonic form without much irritability of stomach, bitter tonics such as nux vomica, calumba, gentian, or quassia, along with some of the mineral acids taken before, with, or immediately after a meal will be found highly serviceable; while on the other hand, when there is gastric irritation with acid eructations, sickness, and pain, the medicinal hydrocyanic acid along with bismuth, and antacids taken after food will often afford relief. Pepsine is a remedy of undoubted value in many cases of dyspepsia, and appears to supply the place of that ingredi ent of the gastric juice when it is deficient in amount. It may be given along with a meal, alone, or in conjunction with diluted hydrochloric acid, which also is a remedy of great efficacy in indigestion. Strict attention must ever be paid to the regular action of the bowels, and where laxatives are required an aloetic dinner pill, or, what is often better, one of the mineral bitter waters (such as that of Frederickshall) which are now so commonly used, should be had recourse to.

The employment of alcoholic stimulants to assist digestion is largely resorted to both with and without medical advice. While it seems probable that in certain cases of atonic dyspepsia, particularly in the feeble and aged, the moderate administration of alcohol has the effect of stimulating the secretion of gastric juice, and is an important adjuvant to other remedies, the advantages of its habitual use as an aid to digestion by the young and otherwise healthy is more than questionable, and it will generally be found that among them those are least troubled with indigestion who abstain from it. See PHYSIOLOGY and DIETETICS. (J.O.A) |

DYVEKE, in German often Düveke, and in the Latin chronicles Columbella, the "Little Dove," the name by which the mistress of Christian II. of Denmark is invariably designated. Her father was a certain Sigbrit Villums, who had been obliged for political reasons to leave his native country of Holland. Settling at Bergen, he opened an inn, which soon became known for something more than the hospitality of the host or the excellence of his cheer: his daughter's beauty was bush enough for his weakest wine. Valkendorp, the chancellor, did not think it unbecoming of his priestly character to sound her praise in the ears of the young crown-prince; and accordingly, when he visited Bergen in 1507, the prince made a point of seeing the "Little Dove" for himself. In matters of this sort there is unquestionably a royal road; and so having danced with her at a ball or two, he had little difficulty in getting her to leave the inn for a house of her own at Oslo. She followed him to Copenhagen on his accession in 1513, and both her father and mother obtained unusual influence at court. In 1515 the young king, indeed, was constrained from reasons of state to marry Isabella, the sister of Charles V.; but in spite of the emperor's remonstrance, his relations with Dyveke and her parents underwent no real alteration till her sudden death in 1517. That she had been poisoned was the natural verdict of the popular feeling; and the royal suspicion fell on Torben Oxa, warden of the castle of Copenhagen, who was known to have made love to the girl before she was carried off by the prince; and was it not true that two days before her death he had sent her a present of cherries? It mattered not that the culprit was declared innocent by the royal council: "though his neck were as thick as the neck of a bull it should not save his head," raged the king; and he kept his word. Such is the story, not altogether authenticated, which has furnished a favourite theme to dramatist and novelist. Samsoë the Danish poet, published his well-known tragedy "Dyveke " in the close of the 18th century, and it was translated by Manthey into German in 1798. Münch treated the subject in a semi-historical manner in his Biograph.-histor. Studien; Hermann Marggraff's tragedy of Das Taübchen von Amsterdam appeared in 1839, Rickhoff's Duveke in 1842, Hauch's Wilhelm Zabern in 1834, Ida Frick's Sybrecht Willums in 1843, and Mosenthal's Düveke in 1860.

DZUNGARIA, DSONGARIA, or SONGARIA, & former Mongolian kingdom of Central Asia, raised to its highest pitch by Kaldan or Bushtu Khan in the latter half of the 17th century, but completely destroyed by Chinese invasion about 1757-59. It derived its name from the Dsongars, or Songars, who were so called because they formed the left wing (dson, left; gar, hand) of the Mongolian army. Its widest limit included Kashgar, Yarkand, Khotan, the whole region of the Thian Shan Mountains, and in short the greater proportion of that part of Central Asia which extends from 35° to 50° N. lat. and from 72° to 97° E. long. The name, however, is more properly applied only to the present Chinese province of Thian-Shan pe-lu and the country watered by the Ili. As a political or geographical term it has practically disappeared from the map; but the range of mountains stretching north-east along the southern frontier of the Land of the Seven Streams as the district to the south-east of the Balkhash Lake is called-preserves the name of the Dzungarian Range.