Page:Encyclopædia Britannica, Ninth Edition, v. 7.djvu/606

584 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., Ixxii. 770). For filling bore-holes its pasty consistency renders it a very con venient material. In continuous masses dynamite transmits detonation at the rate of from 19,500 to 21,600 feet a second. Con finement 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., Ixxii. G88). 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.

1em  DYNAMOMETER (8wa/u, strength, and perpov, 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 im proved 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 VEcole Poly technique, 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.  DYSART, a seaport town and royal and parliamentary burgh of Scotland, in the county of Fife, nine miles north east 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 combination 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 was 247G.

1em  DYSENTERY (from the prefix Sus, and evrepov, the intestine), also called Bloody Flux, an infectious disease with a local lesion in the form of inflammation and ulcera- tion 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, some what 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 